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Engine Failure Diagnosis (pictures)

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Engine Failure Diagnosis (pictures)

Postby peerless » Wed Apr 16, 2008 6:55 pm

I recently suffered a engine failure of a new engine. The machining was done by a few different shops and it turned into a disaster. I was hoping to be able to openly discuss the subject without being ridiculed for a meat ball rebuild. To be honest I invested alot of money into the short block and to have it fail really hurts the pocket book and a little pride off the top.

The engine in question is a 1985 BMW M20 2.7L I6.

The block was a core block, crank and came with a mixed assortment of main caps from 2 blocks.

Crankshaft:
I took the crankshaft to National Crankshaft in Anaheim, CA. They are now EPWI distributors. Anyways I told them to check the crank and micro-polish it. Well without my consent they turned it .010-.010(.25mm). I was a little pissed but paid my $125 and that was it. After some research I found out the did not widen the thrust faces which is required for the BMW cranks, and they also did not re-harden it, which is again required on the BMW cranks. So off to another local machine shop who properly widened the thrust surface and nitrided the crank along with reworking the poor chamfering of the oil holes and a micro-polish. That was another $300, so $425 into the crank all because the original machine shop didn't listen to what I wanted done.

Block:
The block and a set of main caps was sent to a machinist my friend recommended. He does great work but has never delt with BMW engines, not that it should matter. So this machinist sends my block out to get align bored and honed since I had mixed/matched caps. He sends it back down the hill to the same people who initially mis-machined my crank in the first place. When the block came back he bored/honed/decked the block. The machine work looked really nice. He had the pistons and the spec sheet in the box. He said he checked the main bores and everything was in great shape.

Bearings:
I went with Glyco/Federal Mogul bearings instead of the factory bearings for price reasons. The Glyco bearing is a 360deg oil grooved main bearing. The factory bearing is a 3/4 oil groove design. Glyco $90 for the mains, Factory $230 for the mains. The rod bearings are standard issue from either source. I sent the bearings to HPC coatings and had the rod and main bearings coated. This was another $125. They where all black and bitchen looking when I got them back. But on closer examination the coating appeared to be awfully thick and appeared uneven in a few spots.

Pistons:
The pistons where manufactured locally in Long Beach, CA by Venolia pistons. They are a higher compression duplicate of the factory style piston. Forged 9.5:1 86mm pistons. They looked great, had shorter side skirts and weighed in at 345grams each. The skirt size is 3.342". I used Deves rings and they where supplied to Venolia so they could machine the correct ring lands. The block was decked .005" so that may add a little to the compression.

Assembly:
Now mind you I am a home builder so my ability to properly check the machine work is limited. So I am at the mercy of the machinist and have to trust the work is done correctly. I have now learned first off that is a very foolish practice. I have learned the hard way and this story is testament to that. Ok, so the first problem that crops up is the crankshaft won't fit into the block. It won't clear the thrust bearing. This is when I found the crank was mis-machined as mentioned above. So the first reaction my friend has is to try to clearance the thrust bearing.

Ok, so I get a new factory thrust bearing and the crank is re-machined and where on are way again. Next problem, the coating on the bearing is so thick that the crank is hard to turn. Check the clearance with some old fashioned plasti-gauge and we have .0008" ! That by the way is the minimum factory spec. so technically were in spec, but its still way to tight. So out come the bearings and we hit em with a scotch-brite pad and take down some of the high spots. We assemble it back up and we get .0011. Its still pretty tight, but its in spec and the coating should wear down a bit and I will be about .0015 which I am told is good for a street motor. The rods went fine for some reason and had .0018 clearance as I remember.

Now we come to the pistons, and again I have no proper way to check the bore size. I get the skirt in the block and it feels kinda loose. The only thing I have to try and check with is a feeler gauge. Smallest one being a .008. It wont go but it feels really close to going so I 'assume' I have about .006 clearance, so .003 on the sides. I ask about it and am told that they are billet pistons and will expand alot. Advised I may experience some minor piston slap when its cold. Ok, sounds reasonable. So the pistons are ringed up and rodded. Short block is done. Its crank is on the tight side and the pistons are on the loose side, makes me wonder if this damn thing is going to live. Well its not.

Failure:
I get a head on it, in the car. Prime the oil pump in similar fashion to the drill and oil pump rod. Then disconnect the ignition and crank it over, seems to crank over fine, oil pressure goes up. Hook up the ignition and it fire right up. Here theres a good thing. I only had headers and down pipes on it so its pretty damn loud and sound good. I hold it at about 1500-1800 for about 10mins and let it get up to temperature. Every thing is good so far, no leaks, runs smooth as a kitten, just loud. So I take it over to the exhaust shop and get the pipes all hooked up and as soon as I start it up, every body looked at each other and said "Thats not good". It sounded like a cummins diesel. Piston slap like a wiped out old engine. So I drove it a little bit to see if I could heat it up enough, but the noise never went away. So at this point I got mad, and drove that SOB because I knew I had to tear it down. I knew it all was coming and if I had the proper measuring equipment to check everything out I could have caught the bad bores and started on a new block.

I am hoping to be able to reuse the bearings and possibly the rings. If I had the money I wouldn't hesitate to replace it all. But....

Anyways all comments are welcome. Very curious to get some feedback on the wear patterns of the bearings.

Here is the block when I first got it back from the machinist. Looks really good. The bore size was supposed to be 3.346. After the failure I borrowed a bore gauge and got 3.350. The pistons are 3.342. It ended up being .008" total skirt to cyl wall clearance. I have no idea how the machinist could have made some much clearance into it.
Image

This is the #1 rod that seem to take a little bit of a beating. The bearing itself is not damaged but all the coating in that area got wiped off. The flash makes it look worse then it is, but I still wonder why only this rod bearing took a hit like this.
Image

This is a picture of the #5 and #6 rod bearings, all the others look like this with very little wear as compared to #1 pictured above.
Image

The crank itself took no damage at all. All the other rod and main journals like like this.
Image

Here are the piston rings:
Image

And the main bearings. The block bearings on the left, cap bearings on the right.
Image
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Postby ralph85 » Wed Apr 16, 2008 7:25 pm

So what failed? Did you just react to the noise it was making. what is your compression and have you checked it (cc)? could the sound you were hearing have been detonation?

sorry to hear about your experience. hope you get it figured out.
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Postby Dodge Freak » Wed Apr 16, 2008 8:27 pm

A leaking header gasket can make a loud slapping noise like, I always use RTV on the header gaskets.
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Postby MadBill » Wed Apr 16, 2008 9:02 pm

Guys! 0.008" on a street piston of less than 3 -1/2" bore! No need to look further...
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Postby peerless » Wed Apr 16, 2008 9:10 pm

MadBill wrote:Guys! 0.008" on a street piston of less than 3 -1/2" bore! No need to look further...


Exactly!

The pistons where rattling around so bad. Sounded like 2 skeletons fuching on a hot tin roof!
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Postby Dodge Freak » Wed Apr 16, 2008 9:38 pm

Thats a small bore. Not really in to those small motors.

Heck the machine shop screwed up big time then. Guess you be needing new pistons, either custom or take it out to the next size-but not sure how much over bore those motors can take, I bet not much.
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Postby af2 » Wed Apr 16, 2008 9:49 pm

peerless wrote:
MadBill wrote:Guys! 0.008" on a street piston of less than 3 -1/2" bore! No need to look further...


Exactly!

The pistons where rattling around so bad. Sounded like 2 skeletons fuching on a hot tin roof!


That sucks!!!! I would be kicked out of the shop for that stupind A$$ mistake? Not that it was a mistake the rookie will remember. If it was mine so be it and start again! :x
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Postby PFC1 » Wed Apr 16, 2008 10:43 pm

I really can't see the rings well enough to say, but it looks like a molly ring in the second groove and the second ring in the top. Do my eyes deceive me?

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Postby want-a-be » Wed Apr 16, 2008 11:26 pm

Hard to tell by the picture....but doesn't it look like the second ring has an unusual amount of wear for the short time that it was ran? This car have a manual or auto transmission in it? A broken flex plate can sound just like a rod knocking sometimes.

Might be way off though.

Don 8)

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Postby needforspeed66gt » Wed Apr 16, 2008 11:34 pm

PFC1 wrote:I really can't see the rings well enough to say, but it looks like a molly ring in the second groove and the second ring in the top. Do my eyes deceive me?

Bret


I would say it looks like you're right.
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Postby peerless » Wed Apr 16, 2008 11:44 pm

PFC1 wrote:I really can't see the rings well enough to say, but it looks like a molly ring in the second groove and the second ring in the top. Do my eyes deceive me?

Bret


The rings are correct. The top ring is 1.5mm, the second ring is 2.0mm. The second ring also has a cut in the lower edge.

No moly rings in that ring stack.

Deves rings are made from the finest Swedish steel, with a composition designed for high heat transfer, low wear, and high flexibility. Being more flexible than cast iron, they seat better, even in worn cylinders. Time between rebores is considerably extended without increased oil or fuel consumption. Break-in periods are shorter, and Deves rings really last - two to three times the life of ordinary cast iron rings.
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Postby Tuner » Thu Apr 17, 2008 2:00 am

It looks like the crank journals weren’t polished well enough and it was assembled with a fair amount of foreign material like dirt or rag lint in it? That’s loose alright, but not so loose it would do any more than shorten ring life and might have poor oil control. I’ve seen Chevy V8’s, large and small, with more than .012” run OK in race boats. This was 40 years ago and the thinking was because the block was cooled with river water the cylinders wouldn’t be as large as with 180° water and the pistons needed more clearance at room temperature so they wouldn’t be too tight when they were hot and the block was so cool. I’m not saying that’s a good plan, just what I saw some people do. Rattled a lot but ran OK. People would hone every time they put in new rings and this was before GM published the advice to not hone when re-ringing an undamaged bore if you were using moly rings.
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Postby DOHCPower » Thu Apr 17, 2008 2:23 am

Image

Whats up with the discoloration in this pic on the chamfer?
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Postby RL » Thu Apr 17, 2008 8:28 am

Do you think the lines in the bearings are from grit because the engine was not cleaned properly.

Forged pistons need more clearance than cast, 0.008" is still a bit big, what does the piston mfg recommend. I remember doing a 4cyl turbo recently with 0.008" and it rattled till it warmed up

Are you measuring the piston skirt at the bottom
Last edited by RL on Thu Apr 17, 2008 8:56 am, edited 1 time in total.
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Postby machine shop tom » Thu Apr 17, 2008 8:44 am

What I see is a lot of vertical scratching on the second compression ring and a lot of scratches in the bearings. These usually come from honing grit left in the block after machining..........

The bores being too much oversize negate using those pistons.

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