2 silly rebuild questions

#21

Sounds like a plan!

#22

One final question before I report back on the results…

I’m got conflicting information on how to use a flex hone. The manufacturer of the tool suggests starting the drill while the hone is still out of the block and insert it while spinning, then remove it from the block after a few passes with it still spinning.

But the document here (http://bmw.ctcms.net/BMW/E-Books/Haynes%20Service%20Manual%20-%20E30%20-%20E28%20-%20E34/02B%20-%20Engine%20overhaul%20procedures.pdf), which is specific to our engines, states the tool should be inserted into the block before turning the drill on, then twisting the tool out manually after a few passes.

Who is right?

EDIT
Started the drill with the tool out of the block, seemed fine. I ran 6-7 passes per cylinder and got a cross hatch between 30 and 45 degrees. I still have a bit of a ridge at the top of the cylinder. Nothing I can really feel, only see. Should I run the flex hone through a few more passes, or leave it as is? I don’t want to take too much material off, but I want to make sure that ridge is gone.

#23

In almost all cases, if there is a visible ridge at the top of the cylinders, they are worn beyond tolerance. There will be greater wear further down the cylinder. Trying to take out the ridge with a hone, is most likely going to do more harm than good. If you haven’t already, have the bores gauged and see how worn they are. If they are still in tolerance, leave the ridge alone.

#24

The ridge at the top is definitely just carbon, i was able to scrape a little off with a some scotchbrite and almost no pressure. I don’t want to make any real scuffs with it.

I apparently don’t know how to use a bore gauge. I’m getting cylinder measurements of 3.3085" pretty uniform across all 6 cylinders. Maximum out of round on any cylinder is less than 0.001".

If the bores really were that big, wouldn’t the standard pistons/rings that were in there just be slapping around loosely? I must have read the micrometer wrong.

EDIT
This is post hone

#25

Doesn’t sound like the cylinders are being measured with enough precision. Wasn’t the spec for out of round 0.0003"? A cylinder gauge that only measures to .001 or .0005 isn’t going to do it.

#26

I spoke with a machinist here this morning, I read the micrometer wrong and therefore didn’t get my bore size correct before. I was off by 0.0010"…so my bores are all really close to 3.3075", which according to the Bentley is the maximum for standard size bores.

I thought the Bentley also states the out-of-round limit to be 0.0012"? So less than 0.001" (or 0.0010" if I don’t drop the last digit) is ok?

#27

OK guys…it does not matter what the bore size is!!! All you are concerned with is the piston clearance. For this, you must have two measuring devices: first, a dial bore gauge…second a micrometer. The procedure is to zero the dial bore gauge in the cylinder at the largest point of contact with the piston skirt. Second you mike the piston skirt 1/2" up from the bottom. Then hold the dial bore gauge in the mike and read the difference. That is your piston clearance. Do this multiple times for each cylinder and record the results. Do all cylinders. Its not hard, but it is tricky to read the dial bore gauge in the mike. This will tell you the most important clearance for the pistons. This is what must be in spec!!!

If you are installing new rings, be sure to measure the ring gap where the ring actually rides on the cylinder wall. I like to use a piston with a pin in from each side to push the ring down and square it to the bore, then measure/fine/measure/file, etc. for the proper gap. A little large is OK…small equals a broken ring.

Do not leave a ridge of anything in the top of the cylinder. Either remove with the scotch brite pad or use a cylinder ridge cutter. Chuck

#28

[quote=“OriginalSterm” post=57602]I spoke with a machinist here this morning, I read the micrometer wrong and therefore didn’t get my bore size correct before. I was off by 0.0010"…so my bores are all really close to 3.3075", which according to the Bentley is the maximum for standard size bores.

I thought the Bentley also states the out-of-round limit to be 0.0012"? So less than 0.001" (or 0.0010" if I don’t drop the last digit) is ok?[/quote]

Not ok. Measure them to the nearest ten thousandth and find out how out of round they really are. I’ve not looked up the spec but if Richard’s notes say .0003, then I’d orient on that number.

Bentley specs. It took me a while to understand this, but just because something is within the Bentley spec, doesn’t make it ok. For example, the main bearing spec is .0012" to .0028". I first interpreted that as anything between those numbers is fine. That’s not correct tho. .0012 is too tight and .0028 is all kinds of loose and asking for trouble. A fresh engine build should be at .0018 +/- .0002. +/- .0001 would be better.

The whole ballgame of building a motor is getting all the tolerances just right. You keep at it and do whatever is necessary until every damned tolerance is perfect.

.0028" does not represent “acceptable so I can drive on”. .0028" represents “completely not serviceable worn out POS”.

Get the stuff measured precisely. If the cylinders are out of round, you have to decide whether or not you can remove a little material and reuse your pistons, or whether to remove a bit more material and buy new pistons. Your motor can live with larger piston to cylinder gaps, but out of round cylinders are a problem.

#29

I find it hard to believe that someone would publish a number calling it a tolerance if the value is unacceptable. They could put in 3.3" plus or minus 1 inch if all they were saying is it has to be exact.

Is it an optimized number? Highly doubt it. Is it ok? I sure hope so.

Being an engineer, writing specification means the numbers I put on paper better damn well fly. That’s the world I’m coming from. If the Bentley manual is unacceptable, what published numbers should I go by?

#30

Bently is for building a STREET ENGINE. For a race motor, you should have .002 mains, .015 for the rods. Chuck

#31

You should look at it this way. All the min tolerances must be met. If your pistons are at minimum and your cylinders are at max then the clearance between the two would be out of spec. The tolerances are there to know when one part of the system is out of spec. Chuck is right in that you need to measure the pistons and then the cylinders and see what the clearance would be. If it is too much it does not matter if the other stuff is within spec or not. If the max clearance between pistons and cylinder are past max you could then look for different pistons that would meet the tolerance.

#32

I’ll buy that the Bentley is for street…

I should have the piston to wall measurements soon too.

Does anyone have M20 RACE specs published? Or is it a race builders secret?

#33

[quote=“OriginalSterm” post=57764]I’ll buy that the Bentley is for street…

I should have the piston to wall measurements soon too.

Does anyone have M20 RACE specs published? Or is it a race builders secret?[/quote]\

Read below for race specs… Chuck and I both detailed our specs.

#34

Finally ready to break-in the engine, been sitting on the stand waiting to be installed for months now…

What oil do you guys recommend for the break-in? I believe I will be able to break the motor in on a dyno at a local shop next week.

#35

Break in has 2 elements, top and bottom. The top needs to see oil with very high ZDDP content in order to coat the cam with a molecular layer of anti-wear material. I’d either use a “break in oil” or use some cheap generic oil with anti-wear additive. If you intend to run the engine long enough for it to get hot, then use a high visc oil.

The bottom is less clear. There’s plenty of advice on the Internet re. oil choices and helping the rings to seat but I don’t know what to believe. Ring lubrication is mostly, but not entirely hydrodynamic, like bearings. That is to say a “cushion” of oil and no metal to metal contact. Only to a lesser extent is there direct metal to metal contact like the cam. So maybe if it’s “mostly hydrodynamic” lubrication the process is “mostly” not sensitive to oil choice.

For example, some people say “don’t use synthetic oil for break in because it’s too slippery”. But if there’s darn little metal to metal contact when your rings are moving, is “too slippery” really that much of an issue. I don’t know but it would seem to weaken the “too slippery” theory.

I would call up the ring manufacture and ask them for their preferred break in process and oil. Different ring materials have different break in procedures and it’s important to get that right, so a call to them is indicated anyways. And while you have them on the phone, you might as well ask about oil. Or maybe they have the info on their web site.

#36

Brad Penn makes a great break in oil…what I use and recommend. I also use the 10 w 30 race oil.

First start: start, verify oil pressure (hope you have a real gauge) and increase rpm to 2000-2500 and let motor totally warm. (do not let it idle) I like to use an infrared temp gun to verify the temp of each exhaust port as roughly equal so I know all are firing and you can generally tell when the rings seat (assuming the cylinders were honed correctly). After that the motor should be good to dyno. Chuck

#37

I know I read a trick to on here to prime the oil pump, but cannot find it again. Do I just spin the gear (with an electric drill on the bolt head) for the intermediate shaft? Or do I pull the little cap from the side of the block and spin the pump shaft that way?

#38

Priming the pump is kinda of a pita. Easier solutins:

  1. Pull fuel pump relay and run starter for 60sec.

  2. Remove oil cooler from the oil circuit by pulling the oil filter adapter off. Then use an E motor adapter to thread the oil filter right on to the block. This creates a very short path for oil.

But if you really want to prime the pump, pull the access port off of the side of the block. It’s not threaded in, but if it’s never been removed it can be hard to get off. Use some channel locks to get a little twist to/fro going and then you should be able to get it off. If you can’t get it to twist a little warm up the block with a torch, and then put a couple ice cubes in the access port.

Pull the gear out and use an 6mm(?) socket on a power drill to turn the shaft that goes down to the pump. Turn CW. You will know that oil is pumping when the drill bogs down.

This assumes that you’ve got some oil in your cylinders so they aren’t entirely dry.

#39

So don’t use the gear on the intermediate shaft for priming? I’m not sure where I heard that (might have made it up in my head…).

I have some 30W non-detergent oil and some Lucas break-in additive already in the garage, but I might look into that Brad Penn stuff…

#40

[quote=“OriginalSterm” post=64938]So don’t use the gear on the intermediate shaft for priming? I’m not sure where I heard that (might have made it up in my head…).

I have some 30W non-detergent oil and some Lucas break-in additive already in the garage, but I might look into that Brad Penn stuff…[/quote]
In order to use the gear on the intermediate shaft for priming you’d have to remove the tbelt. I’m sure it could be done that way but usually by the time the engine is ready for priming, the tbelt is already on.

You want to prime the oiling system just before you start the car, not just before you install the engine.