I blew an engine a while back and and picked up a used one that I’d like to rebuild before installing. I’ve seen lots of good tips here, but is there a good step by step guide or a good thread with all the little things that I should be aware of? I’m a newbie, but will be working with a a friend who is former shop foreman at a dealer. He has rebuilt engines, but for everyday use not tracks. Also, he isn’t familiar with BMW, do I’d like to be able to point out things that he may not be aware of. Also, is there anyone in the northern Virginia area who has experience with this and can anyone recommend a machine shop? Thanks.
Engine Rebuild Help
SurferShawn
#2
Id say give these 2 articles a good read and see what sort of questions they may conjure up for you! Pages 44 and 50.
Som
#3
I picked up a long block recently with plans on replacing my ~200k motor when it goes. Been doing a bunch of reading up, trying to figure out what I need to replace and what things I can do myself vs. take to a shop. The step by step stuff I expect to get from the Bentley. Given the forum, I expect you’re rebuilding for SE30 racing?
I’ll give you a rundown of my findings. Full disclosure – I’ve never rebuilt a motor, but, like you, am taking on this project for the first time and have been trying to read up on it. People can chime in if I’m on the wrong track. Think of it as me hijacking your thread to get help for myself, but also to help you. 
First of all, a few pages I found particularly helpful here were:
M20 description: http://www.e30zone.net/e30zonewiki/index.php/M20
Parts list (with suggestions regarding which parts should be replaced): http://e30performance.info/viewtopic.php?f=21&t=269
Head rebuild step-by-step: http://www.e30zone.net/e30zonewiki/index.php/Stripping_and_Rebuilding_an_M20_Cylinder_Head
The high level rebuild process looks like this:
- Tear down
- Clean
- Inspect
- Replace parts, as desired
- Prep mating surfaces
- Reassemble
1. Tear down
I haven’t even begun this part – my motor is on the stand, but that’s about it. Only special things I’m aware of here, so far, is that the bolts come off in a particular sequence (and maybe even in stages) to prevent damage to the head. Long spinning parts like the cam/crank also likely have a special bolt removal process to ensure even distribution of pressure as it’s removed to prevent damage.
2. Clean
Seems there are many ways people use to clean their engines. The head can get hot tanked or blasted. Not sure of the most common medium to use for blasting, but I was considering soda blasting as it seems like it might be the best option for a few reasons. One, it’s a home garage and sodium bicarbonate can be disposed of without issue. Two, it’s water soluble so you can rinse off whatever you’re cleaning and not have to worry about the medium getting stuck in random tight spots.
I’d probably blast most of the internals I’m planning to reuse (more on those later).
As for the block, there seems to be some question as to whether this should be hot tanked due to the lack of availability of the intermediate shaft bearings. The M20_Fever (who posted the E30Performance post) mentions that it’s a myth that the bearings are no longer available, but he seems to acknowledge difficulty finding them. It’s worth noting that post is almost 6 years old, so availability could have changed since. I need to do more research here, as I would have liked to have had this tanked.
An option for manual cleaning includes using oven cleaner.
3. Inspect
4. Replace parts, as desired
What you’re left with is the parts listed in the 2nd page linked above. I’ll go through each one and kind of add my 2 cents on what I think I’ve picked up by reading stuff. Again, hoping the people that know better can correct me where I’m wrong. Also, I’m covering strictly the long block without valve cover/oil pan/plugs/injectors/manifolds/accessories.
Also, I’m gonna go in order of the items on the E30Performance page.
Head bolts
What they are: These bolts keep your head attached to your block. Since the head experiences the same amount of force as the pistons during combustion, these bolts are beefy and numerous (14 of them). These bolts are TTY/torque-to-yield/“stretch bolts” – meaning they should be used once and then discarded.
What to do: Particularly if it’s a race motor that’ll possibly (probably?) see more rebuilds in the near future (few years?), it’s probably worth going to studs. That said, I have a friend who tracks several cars who always reuses TTY bolts despite the bolts supposedly being “single use”. He says he has yet to have an issue arising from reuse. That’s just one data point, though, and I’m sure 100 more experienced people will say these should absolutely be replaced. I’ll probably be going to studs anyway, which are not TTY, so it won’t matter.
Intake/Exhaust manifold studs
What they are: Studs that stick out from the sides of the head where the intake/exhaust manifolds attach to.
What to do:I expect, since my engine looks like it’s been sitting out for a little bit, I’ll probably change all of these studs. Haven’t looked into whether it’s a good idea to have these on the head if I hot tank it or if they’ll need to be removed. If they get hot tanked with the head and look nice and straight when clean, I’ll probably leave them.
Camshaft
What it is: This shaft runs down the center of the head through a series of tight circular passages that are part of the head casting. I’m sure there’s a better term for the passages in the head, but I can’t think of what it is right now. The lobes on the camshaft will make direct contact with the rocker arms and control the timing of the valves opening and closing, as well as how far the valves open/close.
What to do: Haven’t researched how to inspect the cams yet. I’m hoping I won’t have to change mine. Not sure if actual damage (like pitting/scraping/etc) to the lobes is common – I’m guessing not, but it could happen. More likely, I think you’re just checking to make sure the dimensions of the lobes themselves are within spec. There’s possibly a test to ensure straightness of the cam itself, though I’m curious how likely that is to be a problem if it was installed/removed properly.
Rockers/Rocker shaft
What they are: The rocker is a lever that translates the shape of the camshaft lobes into the linear in/out motion for the valves. There are 2 rows of rockers – one for intake and one for exhaust. Each row pivots around its own rocker shaft. I believe the shaft is hollow with holes in it where oil is pumped through for lubricating the rockers.
What to do: This depends on what the purpose of the rebuild is. If it’s “normally” driven DD, I’d probably just inspect, clean, and reuse. If it’s a Spec E30 car, I would replace with the beefier IE HD arms, which are legal for the class. If it’s a performance build that isn’t restricted to SE30 rules, there’s possibly even beefier options out there.
I don’t think the rocker shaft generally needs replacing, though I guess if anything looks out of the ordinary with it, it’s probably worth doing.
Rocker eccentrics
What they are: These are small circular discs with an off-center hole drilled into them. They bolt to the other end of the rocker arms from the camshaft and make direct contact with the top of the valves to push them down into the cylinder. The reason they are off-center (or “eccentric”) is to allow for adjustability. There is a very specific distance that the eccentric should be from the top of the valve. I believe this distance accounts for several factors including the ability for lubrication to be applied, as well as the expansion of metals when the engine heats up.
If the gap is too small/tight, you run the risk of wearing down the valve/rocker/cam prematurely as well as potentially altering the intended timing that’s being dictated by the cam. For example, with no gap, I’m guessing that once the engine heats up you would have a case where the valves never fully even close.
If the gap is too large, you would expect to hear ticking sounds when the engine is running and you wouldn’t get as much lift from your valves – resulting in less than ideal flow in or out of the combustion chamber. There doesn’t appear to be anything that actually keeps the rockers “pressed” onto the cam – so, effectively, the rockers are “floating”. If you’re too loose, you can imagine the rockers being “slapped around” back and forth by the cam/valve spring return action. At least, this is how I’m imagining it.
As the motor wears and the cam/rocker/valve stem tip wear down over time, you can imagine that without a way to adjust, the gap between the rocker and the valve stem would keep getting bigger and bigger as more metal wore away. The reason for the eccentricity is to allow for simply adjustments for this wear without tearing down the motor. You can simply loosen the eccentric, rotate it so that a larger part of the disc is facing the valve, and retighten it.
What to do: Well, since the eccentric is now a wear item, too, it makes sense to replace this. They’re cheap enough and replacing them ensures that you’ll be able to adjust the gap to within spec for a long time to come.
Intake/Exhaust valves
What they are: The valves control the flow of gases into and out of the combustion chamber. The edge of the valves need to mate perfectly with the seat on the head when the valves are closed to prevent leaks. The stems run through the intake/exhaust ports in the head up to the rocker arm/eccentric. Since the valve runs through the port, the shape of the valve has an impact on the gas flow in/out of the combustion chamber.
What to do: Inspected for wear – like ensuring the end is long enough so it can be properly gapped. I imagine you’ll also want to ensure the valve stems are straight and the valve lips themselves don’t show any signs of damage. Other than that, I’m thinking this’ll be soda blasted and reinstalled. You’ll want to make sure to keep track of which valve goes to which port so you don’t have seating issues from slight imperfections that have come up over the years. When reinstalling these there’s a process to help mate the valves to the seats again where you’ll apply a gritty paste (ie “lapping compound”) to the valve seats and spin the valve against it to kind of clean the two up and ensure seal.
Valve Stem Seal
What they are: Not sure. But my guess is that this seals the hole in the intake/exhaust ports where the valve goes through it.
What to do: Looks like they’ll be replaced when the valves come out.
Valve Springs
What they are: Where the rotation of the cam and the geometry of the lobes applies the force to open the valves, the springs apply the force needed to close the valves. The springs should be strong enough so that the valve closes with the geometry of the lobe on the cam. For example, if the spring isn’t pushing the valve closed hard enough, you can imagine that once the cam lobe has reached its top and is now on the decline (ie, dictating the rate at which the valve should be closing), if the spring isn’t applying enough for, the valve is going to be left floating until the spring eventually returns it back to a fully closed position. As you can imagine, this would also be dependent on how fast you expect the engine to rev. At slow speeds, the spring may have enough time to close. As the engine reaches higher RPMs and the cam lobes are whizzing by, if the spring isn’t up to the task, it could leave the valve open longer than it should be. On the M20, which are interference engines, this means a high likelihood of causing damage from the floating valve coming into contact with the piston.
What to do: I imagine a simple height measurement is enough of a test to ensure the springs are within spec. If not, replace. What I’m not sure of is if it’s possible for the springs to be worn without the height changing, in which case you’d need a tool for measuring spring force. The engine I’m rebuilding has 200k+ miles on it so I’m probably going to be swapping these blindly, but I’ll probably do more research first.
Expansion Plug; 45mm Diameter Freeze Plug
What they are: I’ve read 2 things about these. One is that they’re plugs designs to pop out if the water/coolant freezes to prevent damage to the block from expansion. I’ve also read that they’re more just an artifact that comes from how the coolant passages are created when manufacturing the blocks. Could be both.
What to do: Replace them. They’re cheap, and make the engine look better when they’re new.
Pistons
What they are: They take the force from the combustion in the cylinder and, along with the rods and crankshaft, help translate the linear force to rotational force. The pistons attach to the rods with a “wrist pin”.
What to do: Clean them, measure them, weigh them. The pistons should be weight matched before reinstalling. If the weights are off, you grind a little off – I’m guessing from the skirt, but I’m not sure – until the weights match.
What I still have yet to do research on or get clarity about is regarding the wear on the cylinder and how that affects reusability of the piston. The wear in the combustion chamber comes from the rings and the cylinder sliding against each other. The rings are obviously going to be replaced with a rebuild and are relatively cheap. But if the cylinder walls have worn too much, you might have an issue where the cylinders are getting too big for the piston/rings to fit. In these cases you would need to replace the pistons with slightly larger pistons to make up for the wear. SE30 allows for an overbore of up to .020 inch. I believe this is because the factory pistons/rings can handle that much of a difference in cylinder bore size before needing to be replaced with a larger piston.
Rods
What they are: The rods connect the piston to the crank.
[i]What to do:{/i] If you’re going for a stock or SE30 build, I would just clean the rods and weight-match them (there’s a technique for matching the weights that involves suspending one half of the rod in the air while measuring the other half). You adjust the weights the same way as the piston – find the lightest one and shave the rest down until they match.
Rings
What they are: Each piston has 3 rings that seals the combustion chamber. The rings provide a “squeegee” effect on the oil on the cylinder walls to keep oil from being burned away in the combustion. I’m sure there’s some other subtle things the rings do, too.
What to do: Replace them. When the rings are put on you should ensure the split in the rings don’t line up (there’s probably even a spec as to how they should line up).
Main rod bolts
What they are: The rods connect to the crank shaft with a C shaped clamp that has 2 bolts running through it. These bolts are TTY/stretch bolts.
What to do: If you read my description of head bolts, same thing applies here. They’re supposed to be changed, but I have a lone data point of a friend who never changes them and has had dozens of track days without issue. Though you’ll also hear most experienced engine builders say they should be changed.
Crank Main Bolts
What they are: Same C clamp idea as the rod bolts, but these bolts hold the crankshaft down.
What to do: Hadn’t really thought of it. Probably just replace them.
Crank Rod/Main Bearings
What they are: The term “bearings” here confused me for the longest time. I always thought of “bearings” to mean something to do with little balls that rotate. While there are no balls here, these bearings serve the same purpose – they allow the crank to spin in the block and the rod ends to spin around the crank. They’re apparently made of a softer metal that will wear (I’m guessing to protect the hard crank metal from wearing) and they’re designed with grooves to allow oil flow. Effectively, they create a “barrier of oil” for the crankshaft/rods to spin around. The main bearings go around the crank’s “main journals”. The rod bearings go around the crank’s “rod pins” or “pin journals”.
What to do: This is also something I need to do more research on. My understanding is this, so far: There’s a specific amount of allowable tolerance between the bearing and the crank. Measuring this gap can’t be done with a typical feeler gauge, so it’s done with a “plastigauge”. Plastigauge is basically putting a soft plastic material between the crank surface and the block/c-clamp that is going to clamp around it (no bearings inserted when taking this measurement – you’re measuring the total gap). Then you take it apart and measure the deformed plastic to determine the gap size. The size of the bearings you buy is dependent on how big this gap is as you’ll want it to take up enough of the gap, but not be so big as to prevent the oil barrier from forming. One reason I’m not sure of this line of thinking is that places like IE seem to just sell a single set of bearings at factory size and I would have expected some options there if it was common to need different sizes.
On an old engine, this has probably worn down significantly and should be replaced. Also, there’s a couple types of these bearings depending on the M20. You can read about it here: http://www.iemotorsport.com/bmw/E30-engine/m20mnbrng.html
Crank
What it is: Converts the linear force from the combustion to rotational force.
What to do: I believe this just needs to be inspected for the journals to be smooth and the right diameter. If there’s damage to the journals, it needs to be inspected to determine whether it can just polished away or if it would take too much polishing to stay within the specified diameter. If the damage isn’t deep enough, then it can just be polished. Oh, and I’ll probably be cleaning this, too.
I haven’t gone into all of the seals/gaskets/whatever as I don’t really know where they all are. The M20_Fever post covers a bunch of them, though.
5. Prep mating surfaces
I’ve actually run out of time with this post for now, but I’ll come back to it later. High level for this section:
Honing the cylinder walls
Decking the head, as necessary
Decking the block, as necessary
Lapping compound on the valve seats (covered above)
Polishing the crank, as necessary (covered above)
Polishing the cam, as necessary (covered above)
6. Reassembly
I’m not really going to write up the how to for this, but as I find links for instructions I can post them back here.
Another thing I need to look into is any kind of special oil properties to use during startup (or maybe even the duration of the motor life). In particular, there’s a lot of discussion around needing to run oil with high ZDDP content.
Ranger
#4
SOM, that was a good post. Some thoughts:
- Cleaning block. Don’t blast it with anything because of the risk of getting debris into something that will later take out a bearing. Don’t hot tank it because intermediate shafts are more of a pita then just sourcing a different block. Just use a pressure washer and blast the heck out of it. If you desperately want to clean the oil galley, you can pull access it by pulling a little plug in front of the block. Then you can blast water into it and also rod it with a rifle bore brush.
My suggestion would be to soap it down with something strong then pressure wash the crap out of it. Then soak it in WD40 immediately so it won’t rust.
-
Valve guides. These are brass? cylindrical little puppies that press fit into the head. Don’t replace them automatically, just tell the shop doing your head to inspect them and replace them as needed. Tell them that since it’s a race head “a little” loose is ok.
-
TTY bolts. I re-use my TTY bolts. Most would not agree with this. Some years ago I found a Mercedes spec re. re-using TTY headbolts. As long as the bolt head not stretched some amount, it could be reused. I don’t recall the #, but it was something around 2mm. Since then I’ve just checked the used TTY bolts against new ones. If they were the same length, I used them again. So far I’ve not seen one that had measurable growth.
I’m not expert at this, I just play one on the Internet. This is do-able as a DIY if you let the machine shop do the headwork and you have a lot of luck. There’s so many ways bad luck can kick your ass on this, that every scrap of precise guidance you can get becomes precious. Be obsessed with measuring. Keep at it until you can reliably get the same # within a couple ten thousandth.
cwbaader
#5
The one thing that everyone misses on these motors is the oiling system. Contact Ranger for a part, and baffle the crap out of the oil pan. Better still, buy a Paul Poore pan. (no affiliation…helped him get it to the final configuration…which means sans PRV.)
Ranger
#6
Chuck makes a good point. The primo solution is both a crankscraper and also a baffle. The engine\oiling system subforum has a write up on most every solution available to us. At least one outfit will sell you the oil pan with a baffle pre-installed. The Poore pan is killer, but pricey.
I think that Rich Bratton was making and selling some oil pans that have are baffled and have a right side door. I made a couple and sold them but right now all I have is my spare. That outfit that I referenced above was selling pans at a pretty good price. Unless Rich was willing to make one for you, I’d just buy a pan from them.
FishMan
#7
A few notes after reading that super long post.
Don’t blast any internal part to include your oil pan, valve cover, or intake. Glass beads will hide from you then wreak havoc by dislodging and circulating throughout your engine. Instead, use degreaser, soapy water, and even oven cleaner (for cooked on oil sludge in the oil pan) then dry with compressed air. I literally spend 50% of my time cleaning parts when building an engine.
Pressure wash your entire engine before disassembly then wire wheel to remove paint and rust. Expect it to return from the machine shop somewhat rusty. On intermediate shaft bearings, they rarely need replacing but are easy to order with the correct part number. The tricky part is fitting the IM shaft bearings, but a competent machinist can handle the job. You can actually remove the IM shaft bearings, hot tank the block, then replace the used bearings if you desire. Hot tanking doesn’t do much for rust so be prepared to wire wheel after.
On your cylinder head, replace the guides… Do the whole job the first time and you’ll be able to freshen the head a few times without touching the guides. I’m not a believer that loose guides is of any benefit, but they will certainly wear out faster. Metric Mechanic and VAC sell guides with high mangenese valve guides that you can run really tight (less thermal expansion), but OEM guides will suffice unless you have money burning a hole in your pocket Stick with tolerances on the tight side.
Stay away from head studs. They don’t provide a benefit for NA motors and could make removing the head in car more challenging. There are reuseable head bolt solutions (final torque 55 ftlb) from Metric Mechanic or Metric Blue bolts. However, OEM bolts are stupid cheap. There is nothing magic about the reuseable bolts; they are just grade 12.9, M10 x 150mm cap head bolts.
When you remove the rocker shafts, move the rocker arms around so none are applying pressure to the cam. Drive the rocker shafts out with a brass drift to avoid mushroom or damaging the shaft plug. Avoid using a socket extension applied directly to the shaft because it will cause damage.
Unless the can is extremely low mileage, replace both the cam and rockers. Both the cam and rockers wear and visible inspection may not help ID the wear. I once went through a bucket of rockers, installed them one at a time in a head then measured lift with a dial indicator. Even rockers with very little visible wear had considerably reduced valve lift. Eccentrics on the other hand can be re-used if they don’t have flat spots or burrs. Febi cams are $150ish and should last for the life of your car. IE HD rockers and OEM BMW rockers are rock solid. Febi rockers have a bad reputation, but I know of several race cars using them without issue.
Pistons can be weight matched by removing material from the pin boss inside the piston. Do not take material off the skirt. Rods need to be checked for roundness with a dial bore gauge; most of the time they are not round and need rebuilt by a machine shop. Cylinder bores are normally out of round as well. Most of the time it doesn’t make sense to true them unless you bore to oversized pistons because it will increase the piston to cylinder clearance. On piston clearances, tight (.0017") is good with cast pistons. Ring gaps should be on the tight side as well.
Replace rod bolts, but reuse main bearing bolts. Rod bearing and main bearing clearances are very important and should be checked with a dial bore gauge. Follow the .001" per inch of bearing journal rule. Ideal clearances are .0017" and .0024" for rod and main bearings respectively. Most of the time, factory replacement rod bearings will be too loose. Clevite makes under sized bearings that fit better.
Most importantly, measure everything and only move forward when parts fit correctly! If a clearance is quite right or a part doesn’t fit correctly, there is a problem that should be addressed before moving forward.
Good luck and let us know if you have any questions or need help!
cwbaader
#8
I like to use a pressure washer on an old block after it comes back from the machine shop. It is usually full of honing oil containing metal and rock. I wash out with purple power and the pressure washer paying special attention to all oil galleries. Immediately wash down the complete block and oil passages with WD40 to prevent flash rust. Usually takes me a good 30 minutes with the pressure washer!! After the WD, blow off/out with compressed air and paint the outside. Then you can start assembling the motor.
Som
#9
Damn, lot of good feedback here. I was going to go through and update my original post to fix some of the typos and brain farts, but it looks like we can’t edit posts…? Or am I missing where that button is? I was also going to incorporate some of the later posts to make it a little more useful for people looking at it in the future.
I found another interesting thread regarding valve adjustments using the “spring tool” that I was going to add to the thread: http://www.r3vlimited.com/board/showthread.php?t=277021
Fish, wonder what your experience is with soda blasting. It seems to alleviate some of the concerns around using non-dissolvable media. Since the soda dissolves, sounds like you’d just soda blast, rinse, WD40.
I also wanted to add the information on the guides. I didn’t see them brought up in a few of the more comprehensive threads I’d found, and then I read that some engines don’t have them, so I wasn’t really sure if the M20 did or not. Sounds like they do. Is this something that is pressed into the head? There was something I read about a part where freezing the part/ovening up the head to “no more than 400 degrees” helped install it. Wonder if this was it…
Good feedback on the head studs. With my buddy’s experience + Scott’s experience, I’m actually considering reusing my head bolts now.
Surprised to hear about the cam replacement being likely for older motors. There’s got to be an easy way to measure the lobes to determine whether they’re really that far worn, right? I mean, if the cam is really $150, I guess that’s not that big a deal… guess I thought it would be more than that.
I didn’t think about the rods being out of round. Does this mean the journals would be out of round, too? Is there a spec for how how out round the rods/cylinders/journals can be? (if so, I’m guessing it would be in the Bentley?)
I’m still curious about my understanding of the piston sizes. Am I correct in understanding that .020" overbore is really just the max diameter that can be used with a stock piston? How much wear does a typical cylinder see? (say, a 200k motor) Would you expect to see something that worn? Is there any advantage/disadvantage to running with the overbore? Seems like there would be a tiny gain from the displacement…? Or is that small enough to fall under the noise.
Som
Ranger
#10
I’d leave the install of the valve guides to the shop with the head. Maybe Rich has done it, I have not.
The spec for the rods being out of round is 0.0004. That’s a pretty tight spec. There are shops that will refurb rods, but it’s easier to just collect more then you need and then use the best 6.
Stating the obvious, you’ll need a bore gauge that can measure a tenthou and you’ll need to practice with it a bit until you can get the same measurement over and over. Most bore gauges won’t do a tenthou. The cheapest way to get good gauges and mics is to get some high quality used ones off of ebay. Or you could just let the machine shop check your rods.
Save your old rodbolts. You will need them when you are installing bearings and measuring things, be it using a bore gauge (best) or using gummies (not best). If you are careful, you can re-use your headbolts several times as you play with torque and bearing thicknesses to get the perfect bearing tolerances. You will feel the rod bolts “give” as they fail. Just go slow and careful and feel what your torque wrench is telling you. ID the relationship between torque and bearing tolerance for each rod. Once you’ve decided on a certain bearing thickness and torque, put in your new rod bolts, some assembly grease, and fasten everything up.
It goes w/o saying that ideally, you’d have the measuring devices and tools to check a lot of the things that the machine shop would be checking and doing for you. In a perfect world, you’d be able to spend time at the machine shop participating in all of this.
Be wary of using my suggestion on headbolts. A lot of people call me a nutjob.
Cylinders being out of round and .020 over pistons. You’ve got some decisions to make. Buying new pistons adds a fair amount of cost. Check your cylinders for roundness. If they are out of round then depending on how bad they are you either buy new pistons/rings, or get a better block. Don’t expect a big advantage with bigger pistons, there’s better places to put your money. I have 3 blocks and only 1 of them is .020 and it’s not been in a car in 3-4yrs. I get my ass kicked, but it’s not because of my pistons.
The gain is more from compression than displacement.
Yes, 0.020 overbore is the max allowed because that is the max OEM piston size. In metric, it’s 0.5mm. Blocks vary. I’ve had good luck and my blocks have all been nice and round, but that’s not always the case. You’ll find a lot of high mileage blocks that still have nice scoring on the cylinders. Rich has a better feel for this than I.
Cam. Measuring cam wear with a mic would be hard. Usually it’s a visual inspection that determines whether or not it’s a go/nogo. Poor oil choices can be tough on cams. If you’ve a couple hundred $$ burning a hole in your pocket, consider new rockers too. Adjusting your rockers don’t entirely compensate for wear. The part of the rocker’s pad the feeler gauge hits is not precisely the same part of the pad that rides up on the cam.
I thought that cams ran around $250. Where’d you find it for $150?
FishMan
#11
Like Ranger said, leave the valve guide work to the machine shop unless you want to invest in several thousand $ is specialized tools. They need to be pressure checked, surfaced, valve seats cut, valves ground and each operation requires different tools.
On TTY bolts like rod bolts and and head bolts, I recommend not re-using. I have re-used rod bolts in a pinch, but most of the time the risk of failure is not worth the small cost in replacing. When pre-assembling rods to measure tolerances or rebuild, use your old rod bolts. You should only use the new bolts in the final assembly process and don’t torque them until you check, and re-check, piston and rod orientation.
.020" over pistons are a 2 to 3 WHP bump in my experience; Some of our very best performers don’t have them.
Reference block roundness, I’ve never run across a used engine (approaching 20 builds), that was not so out of round that over bore was required. Ranger’s blocks were corrected by one of the very best machinists by hand (Jim and Metric Mechanic) and he was able to straighten the bores without removing too much material. Most machinist use automated equipment and can’t straighten the bores without creating excessive piston to cylinder clearance. Because a used block has visible cross hatching and otherwise looks fine does not indicate the cylinders are round and straight. You simply cannot see the problems without special tools and a proper bore gauge is required to measure.
It’s also not easy to visually inspect a cam or use caliper/micrometer to measure wear. Sure, it’s easy to spot a cam with significant wear, but hard to spot one that has enough wear to reduce lift .010" to .015". Without a cam doctor, the best way to measure wear is by installing a cam in a cylinder head, with a new rocker arm on one intake lobe, install the timing belt, then rotate the crankshaft while using a dial indicator to measure valve lift.
The last new cam I bought was $158 shipped from BMA Parts. Prices go up and down. To get the best prices, I buy parts from five or six vendors for each engine build.