Chain Failure Engine. What Next?
 

Hey gents. Gotta spare engine sitting here for awhile. Curious what I have, but didn't really have time to do an autopsy yet.
I was going to gear up to take it apart this winter. Intent was to salvage block, but the seller left the heads and other components on for me. I believe it came out of an 85, miles unknown.
Known cam chain failure passenger side.
For sure cam teeth gone, chain tensioner assembly wasted, head cracked at tensioner.
What else should I expect? I guessing valves bent.
Is there a remote that I could salvage engine with replacement head and cams and tensioner? Or is it a take what you can get off of it and move along?
https://cimg0.ibsrv.net/gimg/rennlis...85bb5e2a44.jpg

https://cimg3.ibsrv.net/gimg/rennlis...f9285bd551.jpg

https://cimg7.ibsrv.net/gimg/rennlis...a9ba762f71.jpg

https://cimg9.ibsrv.net/gimg/rennlis...ec4cdfba04.jpg

get another head and refurbish the left one,
put it back together update the tensioners if not done already.

928INTL might have some used parts for this hint 1/2 price sale

Thanks Stan.
I was hoping that I wasn't just sitting on a glorified coffee table!
I will put up some pics as I go.

Random question for the entire forum: Why two M28 engine numbers? ie., M28 43/44, M28 21/22, M28 41/42 for the S4, etc.
The 86.5 engine I have is a "43" and this one (assuming MY 85) is stamped a "44"
More to the point: was there a difference? Timeline? Location of assembly?

You should have the 928 book it lists all of the engine codes,
the differences are for manual and auto transmissions,
Also the M28/43 gained 20 HP for the US/Canadian 1986 5 speed models,
due to the Bosch Motronic engine management

To expand just a bit, the 'even' 2nd number is the auto version. Odd is manual.

I honestly have no clue on what the difference between an auto & manual engine is.

flywheel and pilot bearing installation for the 5 speed,
different flywheel for the auto
and vacuum line routing for the auto and deleted for the manual and some other electrical changes

Miles were just short of 100k. I got it with 70k mi in the original owner platinum car, 85. Car had sat for over a decade. Did a lot of periphial service to get it running right. Struggled through some weeks lean running, warm running, until I figured out several injectors were clogged. Drove it daily for 5 years. Operated the car for about a year with some ticking noise due apparently in retrospect to loose chain. Ran very well otherwise. One day at lunch I started it and the chain failed. It immediately sputtered to a stop and I could hear the tink tink tink of valve's hitting as it did so. There was no reason to spin it again, I knew what happened. The other head should be fine. Figured it was a parts donor, if you reurect it instead be certain to redo the oil pickup and gasket as it was removed for another project. Block and rotational stuff should be fine. It hadn't been opened up until shortly before you saw it, so it didn't sit collecting shop dust for long while open.

Wow, those pics bring back memories. Yeah I had this happen on my 944S at about 180k miles, same basic results wound up replacing the head over the course of a year, most valves were toast as well. No noise before blowing up.

What concerns me is that the engine had only 100k miles on it? Got a picture of the wrecked tensioner/pad?

Come to think of it, mine blew up on startup as well. Interesting.

There are pictures in a thread here titled 32 Valve Derailment. I don't know how to post the link from my phone. Davek9, one of the Detroit crew you might have met at frenzy this year, has been advising maintaining the pads on 85/6 due to this tendency. I'm apparently one if the handful of fools that ignored the advice and actually paid the price.

Still a solid block with good possibilities for crumpler. He was in the right place at the right time last year when I had to liquidate.

Found the link:

https://rennlist.com/forums/928-foru...erailment.html

Thanks for the back story Mr. Toft.
I want to thank you again for the awesome pricing as well. :burnout:

At the time, I couldn't believe nobody else had beat me up there. Then things got out of control, moderation not being my strong suit, lol.
Anyway, it occured to me, the S3 engines are not getting easier to find out there. I figured if GB is having a harder time finding them then I should try to save it if I can.
It's also a chance for me to get into one of these and learn something.

Thanks for the thread pointer. From the pics it looks like the tensioner pad wasn't broken/bad, more the tensioner itself didn't pump up or was very slack with no oil pressure. I'll look up that TSB, but that could do it.

I'll keep my ears open for the ticking sound, I assume it's a bit different than the normal collapsed lifter one (I have a leaky lifter on the 944S, if the car sits for a month the lifters are noisy for a few minutes, then settle down).

C

Ordered a engine stand kit from Arnworks, but I had some time today to get out to the garage and get the head off.
Observations appreciated.
Intake cam seems intact. Can I trust it?
Exhaust side trashed.
Piston faces looked within normal. That white artifact on #2 is paper towel shrapnel.
Head gasket looked pretty good. Original?
Got a close up of the tensioner and broken casting.
https://cimg3.ibsrv.net/gimg/rennlis...43ff4a6f0a.jpg

https://cimg3.ibsrv.net/gimg/rennlis...948e84d868.jpg

https://cimg6.ibsrv.net/gimg/rennlis...6aa8b099fb.jpg

https://cimg5.ibsrv.net/gimg/rennlis...3c1ce8a01b.jpg

https://cimg1.ibsrv.net/gimg/rennlis...1131a004e4.jpg

I would not use either of the cams again as the cam without any broken teeth could have gotten stress cracks from the upset ,
maybe the cam could be magnifluxed ,
still better to get another set

Likely original

put the valve in a drill chuck and spin it near a straight edge if the valve is bent you will see it

Or put them back in the guides and fill the chambers with kerosene and see if it leaks out. If so, the valves or seats are damaged and go from there.

Great ideas thank you, I will probably do both.

So bent valves get replaced without question but from my research of old threads:

our valve springs usually don't fail and don't need to be replaced...right?

lifters can be rejuvenated, but I got the impression the consensus was to replace all if you are in there?

valve guides always replaced while you are in there...?

If you know a machine shop have them put the valves in their grinder- tell him to just barely grind them,. If they are bent it will show,
You are not looking to have them ground ready for use- just checking for bent

You are quite welcome, Dave!
I am glad to be of help.

Chain/tensioner failure is apparently somewhat common on the 944 engines, although this is the first such failure I've heard of on a 928 engine.

Is this failure as rare on the 928 engine as I suspect...and if so, why?

:cheers:
And help you did.
The only thing about that thread I would change is that one certain party's behavior. That was unfounded and irritated me just knowing you had to put up with it.

So this is why I thought the autopsy would be interesting to the forum. I couldn't find another documented example.
Penny for your thoughts GB.

You can do a quick valve grind yourself for $30 for the suction cup tool and lapping compound. Then mark the seats and valves with a magic marker and repeat. Some people hate this process, but I really enjoy it and find useful. This will allow you to see what is going on with the valves clearly. Also the liquid leak test, but it can be done with WD-40 or anything. I would not necessarily replace the lifters, unless I was sure they needed it, but depends on cost. The reason being that if there is a problem later you can change them without pulling the head. You can easily check the guides just by rattle/feel, but I think 1) they are inexpensive to replace relative the cost the decking the heads (which you MUST do), and 2) they are soft and will normally need replacement in even a medium mileage 928 motor. The first motor I rebuilt had 60K miles on it and the guides were loose.
Regarding the chains, you are totally right. I have not done them on my 944, and everyone who knows the cars yells at me. But it never even comes up in 928 land.

Anything mechanical can fail at any time, that's a given. And the early '85 tensioners were really bad (although I did not look at the serial number to see if your engine had the early '85 version tensioners.....I will.)

If a tensioner collapses completely, it makes sense that the "pads" are going to get really hammered. Once that chain hits metal, I'd think it would be over quickly.

I think we would all benefit from a bit more very close inspection of the pieces....did the plastic chain piece break first and then the chain grabbed?

Thank you JIm!

Thank you Karl. I was watching you tube videos on this and thought it would be cathartic;)

Ok so I pulled the other tensioner tonight...
I was under the impression that they should match config side to side just upside down on one head right?
These don't seem to match, are they different MY tensioners?

https://cimg2.ibsrv.net/gimg/rennlis...a5fcc71f15.jpg

Same design/vintage, just different sides of the engine.

Got it.
So if everything is original then I'm back at the "one in a million" failure scenario.
Are there any other angles, or pics, I can provide Greg?
In terms of the pieces, that's all debris that was in there during my necropsy. I can go back to Landseer's thread and see if he took any pics of the bottom pad or chain.
Anything else to look at?
Thanks for looking.

Dave.

Edit: Actually, there are good pictures on the first page of the thread, pad looks fine, chain broke one place?

https://rennlist.com/forums/928-foru...erailment.html

https://cimg6.ibsrv.net/gimg/rennlis...09e4682189.jpg

I have an 86 S3 head that had the same failure some 10 years back from Big Dave's Black car, pads were not the issue then but can cause the same failure as Greg stated, it's that flat washer inside the tube w/ the spring, it gets jammed, also binds causing oil pressure issues (clacking lifters).
There was a Porsche TSB that replaced the flat washer with a cupped one IIRC.
If the Cam covers are off, just replace them w/ S4's and put on new shoes, everyone likes new shoes ;)

Dave K

So Dave, it sure looks like there was damage to that flat disk.
Close up shows it is chewed into a triangle shape and the channel it sits over on the tensioner is distorted as well.
Crazy. Thanks for the tip.

https://cimg1.ibsrv.net/gimg/rennlis...233adb50d8.jpg


https://cimg5.ibsrv.net/gimg/rennlis...904b1cc4a6.jpg

My neighbor was in front of me that morning going to work.
He took off pretty quickly, I chased him out of the neighborhood with foot into it pretty far for the first couple hundred yards.
(996 T v 928)
Ran great the remaining 11 miles to work.
At lunch, on the start, it failed.

This car, remember, was the van winkler, which was parked with 70K mi and sat a decade in Mass before Stan Shaw and I rescued it.
Was interested in your pic of the headgasket. I had worried about its condition for years based on all the discussion about corrosion.
Had what appeared to be new green antifreeze in it when we got it, but it hadn't been changed in years.

Got the second head off the block tonight, amazing how quick you can do it when you know what you are doing, right?
Anyway, everything else looks good.
I was going to break it all the way down, and then decide if it will come back as a spare stock engine -- or will I go nut$$$ and do a performance rebuild, and then put it in the 86.


https://cimg2.ibsrv.net/gimg/rennlis...20c7913f7f.jpg

I vote performance build. Stick in some GB windage trays, Colin's triflow cams, sharktune it, and enjoy some torque :)

if you swap cams with Colins then you may also be using different valve springs as part of the swap