This is a continuation of my previous thread:
https://rennlist.com/forums/924-931-944-951-968-forum/363387-new-membership-happy-timing-belt-failure-sad.html

I figured since I have pictures now, I will start an official rebuild thread.

Here's a summary of the story so far:
My timing belt broke as I was coasting up an interstate offramp. The crank pully is spinning on the belt and the cam pully is not moving.

I began disassembling the head and have removed the fuel rail, injectors, intake and cam cover so far. Attached are pictures illustrating some of the unexpected things I noticed.

Shown is some gunky buildup in the intake ports, the oil pooling on top of the intake valves, the completely intact chain tensioner, and an odd scratch around the circumference of the cam pulley. Also the orientation of the tensioner pully, for sharky.

This scratch could be from a piece of debris that also caused the belt failure, however I find it hard to believe something big enough to cause a scratch like that slipped past the belt covers. I also did not find any metal pieces sitting at the bottom of the belt covers when i removed them. perhaps it's still embedded in the belt somewhere, which i have not completely removed yet.

As for the gunk buildup and oil pooling - to the best of my knowledge, this engine has 100k miles of light service on it. is it normal for valve guides to leak that badly after 100k miles? perhaps the intake valves contacted a piston, and the force was transferred to the valve guide, or alternatively, after nigh on twenty illinois/wisconsin winters, the valve guide seals are simply brittle and cracked. Hmm, that could explain the trace of blue smoke at high rpms that i was seeing last year . . .

just thinkin out loud here guys - grab a beer, sit back and watch the show - if you're into this kind of thing

 

A possible cause of the oily residue could also be the air/oil seperator seals that reside at the interface between the block and the plastic oil fill tube assembly (properly called the air/oil seperator).

It seems to be fairly common for these o-rings to be shrunken and leaking by now. When this happens, the vacuum in the intake draws air from outside, through the seals into the crankase. From here, the oil-saturated air is then drawn up through the air/oil seperator into the intake stream.

 

sound interesting - i'll check it out.

 

Is it me or are there teeth missing from the belt at that tensioner pulley?

 

Yep, you saw right! This was a situation where teeth were being stripped off the belt. the belt band is still in one piece and looks OK, from what I can see. So I'm wondering - were these teeth going over a period of time, or all at once?

 

Yeah, my intake ports looked alot like that at ~100K. I scrapped away the gooey gunk with an X-acto knife, then wiped with carb cleaner. Then shop-vac'd just in case. But I wasn't rebuilding the head, just changing the ISV and cleaining up the vacuum lines - you could really clean it.

I think you should go after the air/oil separator seals and take a lot of pics so I can see it ;-).

That scratch around the cam pulley is a puzzle, isn't it?

 

Straight up. You know I'm gonna hit that.

And thanks for pitching in - between you and amjf, now I'm not too worried anymore about that gunk buildup. of course, i did just get done reading all about how hard the lower bolt on the AOS is to reach

Amen, brother!

 

I'm also seeing that it looks like the belt was not covering the entire width of the cam pulley. there is a rather significant band of corroded surface towards the back of the cam pulley. there is also a small corroded band towards the front, but it is thin, so it looks like the belt was running closer to the front of the cam pulley than the back. (i'm assuming the corroded surface was exposed and the shiny surface was covered by the belt) is this normal in anyone else's experience? Or is this where the old "OE belt is not wide enough, get the 968 belt" discussion comes from?

 

progress is slow because i'm keeping the car at a friend's house. i won't complain though - i'm just glad he let's me work on it there, borrow his tools, and even takes pictures when i ask!

attached are some images of the head damage - exhaust valves on #3 are visibly bent, don't know about the others yet. machine shop is calling me back today with the results. you can see the small score marks near the bottom of the #3 piston.

#4's piston has a bit more carbon buildup than the other three - not sure what that's from.

anyone know what the best way to get rid of the deposits on the pistons are? i'm planning to rotate the crank until my piston of choice is at the top, and then . . . clean it . . . somehow.

also, must the head studs be replaced?

 

Whatever info you can host on things pertaining to the intake/under it or near it...please post lots of!

I'll be pulling mine this winter for powdercoat and replacing AOS pieces, hoses, and doing some cleaning up here and there.

 

Ok, will do. My AOS is just a big pile of oil gunk right now. Should make for a noticeable change when i clean it.


On a related note -
I just got the quote back from the machine shop - labor costs will definitely be in the minority on this bill! The total comes to $190 for the valve job, $36 for the deck. parts on top of that, of course. This is SPR in Port Washington. They did my flywheel, and I was pleased with the work they did on that, so I brought my head to them too. There was a disassembled 3-rotor sitting on the bench, which was fun to see. Going into a speedboat, apparently.

 

Yea, been there and doin' that too. Broke 2 valve springs, which made me do it.

Lapped the valves, replaced all the valve springs and keepers, getting on the verge of putting it all back together again (I'm tired of having more engine parts in the trunk than under the hood). I had the local engine shop clean the head all nice and purdy so as to make sure all the oil passages were clean and clear.

Replaced the rings while I was at it, so now the fresh engine is going to break the old tired trans for sure! Oh well.

 

Slow progress is an understatement. Here are some pics of the piston cleanup and the belt damage.

I'm actually a little farther than this. The head is back from SPR - cleaning was part of the service so it looks great. I did all the vacuum lines and some of the washer tubing in the interim. After the head came back I put it back on, put the cams in, and then took my first stab at final cam timing. I felt it went quite well, but i guess the proof is in the pudding. Hopefully I'll be able to post my AOS reseal pics and a small blurb on cam timing within the near future.

So with all the hard stuff past, all I have to do now is put the exhaust headers back on, put the intake back on, flush the coolant, change the oil, put the balance belt back on, tension the belts, put the accessory belts back on, put the fans back in, put the starter on and then . . . fire her up!

Oh and to the best of my knowledge - this whole incident was caused by FOD - Foreign Object Damage. Never found the culprit itself, but those scratches on the cam gear are the evidence. I did count bolts and washers carefully when I removed everything and nothing's gone missing, conveniently enough. I did, however, find some rather large gaps in the belt covers where something could have slipped in. The only other option is that the scratches are inexplicable and the belt simply suffered fatigue.

 

Yikes!

Looks like you know what you're doing though. Keep us posted. I so can't wait to tear my intake apart this winter.

Do you think you could post of list of what all you're replacing? It'll give me some ideas as to what I should do.

 

You are planning on replacing that suspect gear right? I would not be satisfied knowing that funky scoring could sever my new belt.