Is it finally time for new motor/rebuild

#1

Ok, here’s my story (I’ll try to keep it shorter than Ranger’s saga).

Car has 204k miles and have raced it for 6 years (3-5 events per year). In the hands of the quicker of father/son duo (you figure out who’s who) it has always been top 5 capable. Never had any motor issues since we started racing it with 192k on clock. Not a single one!

At last Road Atlanta event with Southeast, it was competitive as usual(1:48 compared with 1:47 pole) but then July at VIR it was slow; as in 7-8 seconds off pole and down about 9mph at end of straight speed compared with another car’s Traqmate data. It ran fine with no skipping, hesitation,etc. I did notice my shift points were much later. I was almost not needing to shift to fifth on front straight where normally I’m shifting around timing/scoring.

Today I took it by MotorSports Connection in W-S (well respected BMW race shop) and had it dynoed. I will post the graphs later, but the three pulls were: HP: 141,140,139 and TQ:147,148,146. The AFR was spot on and very consistant. Shop owner says, engine’s tired and time for rebuild. Ouch!

I asked if we didn’t need to do a compression/leak down or something else and he says no need. Car has never used any oil, drips a little but rarely ever have to add a quart.

So now I’m trying to figure out my options.

I’ve actually bought a running 91 325i automatic parts car a year ago to strip some front end parts from. So I guess one option is to swap that engine. Don’t want to spend the $1k-$1.5k to swap motors without knowing if this engine is any good. What would I need to confirm? Dyno? Assume an automatic will show less RWHP due to automatic drive loss. Compression/leakdown test?

Shop recommends a shop rebuild engine to maximize power. Somewhere under $6k. OUCH

Shop checked on crate BMW motor. Roughly same price when installed.

I’m kinda stumped as to which route to pursue and whether additional testing on current engine will yield any additional information.

Thanks for the feedback.

Keith

#2

Do a compression check, leakdown and wet leakdown test. Take the time to understand as well as possible what’s going on, before you start throwing money at it.

Might as well do the same on the parts car.

Take great care with your tests. You can cause a lot of heartache misinterpreting a test.

When an engine is getting weak, refresh the head. The bottom end is more of a matter of bearings then compression. IMO our rings and cylinder walls hold up pretty well, so you get max bang for the buck by just doing a head refresh.

Having said that, it doesn’t cost a helova lot to replace the bearings, but then the slope gets slippery. As soon as you start replacing bearings you start thinking…“gee, I should get it dynamically balanced”, and “lets do a ring/hone job after all”, and finally, “my piston grooves are likely to be worn, ah hell, lets buy pistons and bore out the block.”

Assume for a head refresh that you’re likely to have a worn cam and some worn rockers.

So here’s what to do. If your dry and wet leakdown tests indicate that the compression problem is all head, then plan a head refresh + a possible $250 for cam and some rockers.

Make a decision on your bearings. Pull #6 rod and take a look at it. If you’re not very comfortable with them, then swap to the auto block as long as it’s wet/dry leak down test was good. Look at #6 rod on it too. Note that rod bolts aren’t reusable.

Then you have to decide whether to start throwing more money at the engine (dynamic balancing, ring/hone, pistons, etc) or having the discipline to hold the line. If you do decide on an extensive overhaul, the “one throat to choke” becomes critical. If multiple folks are involved, if something turns out poorly, they’ll all point the finger at each other. It’s simple human nature.

#3

seems a little odd that the motor was fine at one event, then suddenly down 10 hp. wouldn’t “tiredness” manifest itself as gradual loss of power, rather than all at once?

#4

jtower wrote:

That seems odd to me too, but I can’t come up with another theory. Everything else that occurs to me would have shown up as an A/F problem. Jim Levie might have some ideas.

#5

Post the dyno results (including the A/F ratio curve).

#6

I’ll try and get the graphs posted tommorrow. Never done a compression or leakdown test. Sounds like compression and wet compression test is fairly easy. May look to buy me a gauge and see what I find with that. Haven’t found a good writeup yet on the leakdown test.

K

#7

My parts car has been sitting in unheated garage for over a year (and yes I forgot to put fuel stabilizer in it). Should I drain the fuel tank and put in fresh fuel before I fire it up?

K

#8

smithk3933 wrote:

[quote]I’ll try and get the graphs posted tommorrow. Never done a compression or leakdown test. Sounds like compression and wet compression test is fairly easy. May look to buy me a gauge and see what I find with that. Haven’t found a good writeup yet on the leakdown test.

K[/quote]
http://www.gress.org/Home/Cars/TrackTales/track_tales.htm
Link to the leakdown DIY near the bottom. It’s a long-ass write up because I had a lot of problems understanding how the leakdown test is supposed to work. So most of the right up talks about the things you can do to figure out what the heck you’re doing.

The first leakdown gauge I bought didn’t work right. It took me a while to figure that out. And my expensive new head wasn’t done right, and that also took me a while to figure out. So it took me a while to gain some comfort that I was doing the tests right, it’s just that I had a bad gauge and a bad head.

#9

Sometimes putting a nice fresh head on a tired motor will then cause the rings to blow by much more then you first thought. The results are a tired bottom end with new head. I have one of these on a stand in my garage. Fresh top and bottom in the car now.

Michael

#10

might as well do it right and do a top and bottom end refresh.

#11

kishg wrote:

OP: See how slippery that slope gets?

Re. $6k. That’s not unreasonable. But I bet that Chuck Baader will do it for ~$2k plus parts. As long as you don’t change oil pan nor pistons, your parts bill will probably be <$1k. Add $500 if you want him to install it. This assumes that your cam, rockers, and crank are all good.

I pulled my engine, put it on a pallet and shipped it to him for ~$120. Alternately, he’s has Skeen’s old motor sitting in his garage looking for a rebuild and a new role in life. You could buy Skeen’s motor from me, have Chuck rebuild it, then make a roadtrip to his place with your car and the both of you do the motor swap.

#12

Here’s the dyno run from yesterday. Followed up with the shop about doing the rebuild and just before giving the go ahead and then he says… I have a couple in front of you…should be able to start December!!!

AAAAAHHHHHHH! [file name=August_E30_Dyno.pdf size=414391]http://spece30.com/media/kunena/attachments/legacy/files/August_E30_Dyno.pdf[/file]

#13

A/F is really good. Don’t let anything happen to your AFM, DME, O2 & coolant temp sensors.

Your motor is stumbling less then most around the problematic 4300-5000rpm range. That’s where the DME pulls back timing…probably because BMW found that there was a risk of knocking in that rpm range. At least that’s the best theory I’ve heard.

Ya, hp is a little weak. But the scale of the chart makes it hard to see detail. Get the raw data and download WinPep. Then play with the graph scales so you can see more detail.

Still need to do those compression and leakdown tests tho.

#14

Smith

There is nothing more frustrating than to watch the competition pull away on straight away talent.

Curves look pretty good to me. Just not enough power.

It could be many things and I agree with Ranger that you need to eliminate the variables before you start throwing money at a rebuild.

Firtsly - Verify that you are getting WOT. The fisrt time I took my car to the dyno the tech found that I was not getting full throttle travel. Cables stretch over time.

Second - Check your throttle position switch TPS. Skeen gave me this tip a couple years ago. It tells the DME that the car is full throttle and to ignore input from the O2 sensor, thus making max power.

Third - try different DMEs and AFMs - If you have a spare car you already have two.

Fourth - Compression and leak down. Actually this should probably be done first before spending more money at the dyno shop.

If all of the above comes up empty and the comp and Leak down numbers are bad it is time to look for alternatives.

If the leak down numbers are good it could be something as simple as worn out fuel injectors. I had a set that were sent out for rebuild, I put them in, took it to the dyno, and the car made similar numbers to yours. After sepnding hundreds of dollars on fuel pumps, filter, regulator and new TPS the numbers stil sucked. I took the allegdely rebuilt injectors out, put the old 150K original injectors back in and the car ran better. Still not fast but better.

Relative to your spare motor and automatic. I would not worry about drievline losses. Yes, an automatic is not as one to one as a manual but it will give you a good idea of how healthy that engine is.

Good Luck and keep us posted.

Don

#15

also on the WOT…

The throttle body wears out and actually goes over full throttle, look at the stop where the throttle butterfly lever hits, if there is a notch worn into the stop you are going “over” full throttle…

I was told it could be like 5-7hp at top end…

Al

#16

Bought me a compression gage and gave it a try. From front to back I got, 155,155,165,160,152,168. When I first measured I forgot to warm the engine first and I got a 145 on rear most cylinder. I then poured a bit of oil in there and after warming the engine, it went to 168. I took two separate readings on each cyl with turning it over 5 times.

Assume these numbers don’t seem to bad? Heck maybe I got bunch of crap for gas in the last weekend!

Someone also suggested that old tired engines can benefit from a can of something called Restore. Supposed to aid in sealing up pistons/rings and helping with compression.

Maybe that, some fuel injector cleaner and a tank of race gas is all she needs!

Keith

#17

Those compression numbers seem fine to me and inline with what I remember reading on my 200k motor when I first got it. The rule of thumb I have heard is you want all cylinders within 10% so around 15 psi or so, and you are within that.

#18

Compression #'s look ok. Lets see if the leakdown confirms it.

#19

OK broke down and bought a Leak Down gauge from Summit Racing. Played with it a bit until I think I figured it out. Hardest part for me was figuring out how to determine TDC by rotating crank and looking at cam lobes. After I got past that, the leakdown numbers looked good. With a 100psi on the source meter, I got between 5-20% leakdown with only number 3 at 20%. If I understand thats pretty good.

Not sure when valves have been adjusted. If they aren’t adjusted, would that cause loss of power at top end?

Keith

#20

smithk3933 wrote:

[quote] After I got past that, the leakdown numbers looked good. With a 100psi on the source meter, I got between 5-20% leakdown with only number 3 at 20%. If I understand thats pretty good.

Not sure when valves have been adjusted. If they aren’t adjusted, would that cause loss of power at top end?
[/quote]
I’m not leakdown wizard, but since your dyno #'s are low, I’d say you found the cause. A fresh head will probably get you to 3-5%, and a well executed fresh motor to 1-3%.

20% in a cylinder might be ok for a DD, but no way that’s ok for a race car. Once you get >30% leakage your starting to get to the point where there’s so little compression the cylinder won’t fire.

Make sure that you’ve done the leakdown test enough times that you’re getting consistant #'s.

Do a wet leakdown test. That’s where you spurt some oil in each cylinder to seal the rings and retest. A change in leakdown #'s means that you’re leaking at the rings.

Note that the engine’s temp will affect this test. Warm engines are tighter.