Jim bailey - 928 International

T belts do not often break they strip off teeth and then at some point slip . Where and how far it slips determines how many valves hit pistons .When it slips far enough the engine no longer runs . When a water pump seizes (which is rare) the smooth backside of the timing belt keeps sliding past the pulley making it get very , very hot (the engine also starts getting hot due to no water circulation but people try to get to the next off ramp , home , service station ) . Then when they do shut of the engine the belt can melt and vulcanize itself onto the water pump pulley . Typically after things cool down someone decides to "see if it still runs hot" and trys to start the car and then the belt breaks . The timing tension warning is simple and crude , sometimes it tells lies BUT just like the boy who cried " Wolf " it does sometimes tell the truth . Assuming that the warning is false might just cost you $4,000- $7,000 .

Tom. M

ditto on what Jim said...my experience was that the belt was tightened to spec on a cold engine..when it heated up..combination of no oil in tensioner and worn cam gears eventually sheared some of the teeth off. My SWAG is that the overtightened belt ended up 1/2ing the life expectance of the belt..and the cam and oil pump gears were worn to the point where the edges were sharp.

I guess I was lucky in that it happened on start up and ended up with only two bent valves (number 4 cylinder intake valves). The bent valves were nearly impossible to tell until I put water in the intake ports and saw some droplets forming underneath. I would bet money that it would run even with those bent valves, however, you risk damaging the valve seats if you do.

Our local racer (Don Hanson) had his belt break on the track. He was able to replace the belt with the assistance of some others at the track and the car actually ran..not well but it did. When the engine was taken apart..ended up being about 3 valves per cylinder bent...ouch..major ouch...

First thing I did was take the front covers off assess the condition of the belt (stripped clean of teeth about 4 inches either side of crank gear) and also misc. other teeth half missing. Probably happened to have one or two stripped teeth at the crank the moment I cranked the car and did in the rest of the teeth. I pulled the belt, put on a spare used belt aligned everything up..and did a compression test...

Started at number 6..back to #8..good compression..move to passenger side...#1 ..and back...to #4....all had good compression except #4....0 compression...tried a few times...each time..no compression...so there it was...

Again..with 100% hindsight...If I had not cranked the car numerous times...etc..trying to see what the prob was...I may not have even bent the two valves..but...with no idea of what happened..you troubleshoot the obvious....fuel pressure..spark etc....and to do so..you need to crank the engine...even looking down the tbelt cover holes to see if the belt was on...wouldn't have made any difference as it was there...just not moving...

So..if you end up with either a tbelt warning...or the car won't start...check the hole for belt movement first thing..easy and safe..if the belt moves.then likely the belt is ok...you can then move on to the other checks..

I am almost back together....so far.out of pocket about $400...replaced some other parts..WYAIT kind of thing..could have done more..but at this point...just want to get her back on the road.

I'll get a chance to get back at her this Fri and will have it running on Sat.

I would also like to take the time to publically thank a few people in our group for their support and for popping down to lend a hand....Adam B, Thurston P (goldknight), John Davis, Chris F, Rob F, and Dave H . Also to all who expressed their support on our PacNW 928 list and this Forum and the email list....Thanks....It makes the rebuilding process much easier with a support network like this... :-)

Later,
Tom
midlman@rennlist.net
89GT (almost done)

AO

Warren:

Short answer to your last question is yes. You only need the lock to loosen/tighten the crank bolt. And if yours is a manual you don't even really need it. I just put the parking brake on really tight and put it in 5th gear. No problems! Good luck, and do not be afraid to take pictures and post them for additional input as you go.

PorKen

Just after I bought my car, I thought, like many newbies, that I should upgrade my '81 to the HTD (round tooth) belt. (I later found that it's not necessary, unless, of course, you're upgrading to 32V gears! )

Anyhu, I bought a set of '83 HTD gears off eBay and a few months later when I went to install them, I realized that the gear PO had way overtightened the belt; the gears were dipped in the center from the wear, and the teeth were sharp. I kept my square teeth for that belt change.

Aluminum timing gears (cams/oil pump) should be considered a wear item, to be replaced as wear indicates.
...

I read somewhere's that one downside of the round tooth belt is that they are more prone to slip at too low of tension versus the square tooth.

Warren928

If mine was running then all the valves would be bent and therefore it wouldnt run at all. I could see an engine running with 4 valves bent but not the whole engine.

Does anybody know how many degrees or how many teeth it would have to slip for the valves to hit a piston? The ta-ta-ta noise I am hearing doesnt get louder when I revved up the RPM's yesterday, it stays the same. In fact, it gets quieter--either that or the roar of the engine makes it appear quieter.

Warren928

Could the T-Belt plastic covers be cut and made so a person could get a better view of the T-belt and parts without pulling the whole front off the engine? Has anyone made modifications to it?

I may setup something custom for this problem if someone has not already addressed it.
How long should it take to get all the covers off to inspect the T-Belt?

MikeN

Have never seen it done, but I would love to see all the TB covers molded with some sort of clear plastic. But given there are some mounting points, bolt pass throughs, etc.......I don't think it could be made sturdy enough, but what a way to watch and diagnose problems.

AO

Warren,

You should be able to get the right (passenger) cover off without taking much, if anything, off for inspection. The fan is only 3 bolts. IIRC you have to take this off to get at ythe crank bolt for turing the engine. THe the left cover is a bitch to get off. I don't think you can get just it off without taking the front apart. Not a big deal though, 2 hours max.

Warren928

Okay,

I ordered some parts from 928 Int'l to start with. A belt, tensioner boot and a few other things. Hopefully I can put on my mad scientist hat and rip the front of the engine apart soon to inspect the belt.

Garth S

plus ..."Could the T-Belt plastic covers be cut and made so a person could get a better view of the T-belt and parts without pulling the whole front off the engine? Has anyone made modifications to it? "
Plus ..."I ordered some parts from 928 Int'l to start with"
Plus ..."Can I take the front end of the engine off to inspect the belt without the crankshaft locking tool?"

Warren,
If the one family cow is flat- out **** - up in the field, it's not the best time to planning mods for improved cream production: I know this situation would worry anyone, but come back to earth. You need to determine exactly what you have in front of you prior to planning translucent cover mods, ordering parts, grinding cam gears, .....
Either excuse the arrogance (unintended), or accept it: if you go back to my post ( or to any of the guys who have done and posted on this!), and follow the few simple steps noted - you could have already had a reasonable diagnosis in hand. Without that, there is no reasonable idea of either parts req'd nor work to be done.
While there are several ways to do any job - for this diagnostic exercise, you need neither a flywheel lock nor the fans removed ( but working above is nice, so it's another way to do the job), nor the whole front of the eng. pulled.
What you must determine is that if rotating the crank actually turns the TB - if it turns, what shape is it in - if in one piece, was valve timing saved - ..... there is a very logical order to this: invent a new and improved method later, and i'll be amongst the first to follow it.
There is also a reason why the condition of the back side of the belt was mentioned: Jim B made that even clearer, and so on.
So if you choose, take a few tools, and some short steps later, you will have exposed enough to let you know where you are - and where you have to go.
As you now have the links, approach it as if you are retensioning the TB - almost identical.

Warren928

Garth,

Whether it turns out to be a toasted power steering pump bearing or a Tbelt, I am still going to replace the T-Belt anyhow. I want to go in there and make sure everything is okay. I dont want to rely on the laurels of some hack mechanic who only cares if the part doesnt fail for the first thirty days from the repair like most do (and have to by law).

I understand I could just crack open the right cover and take a peek around. I will get to that on Sunday.

To be honest, I dont know if the belt has seen 20k or 45k, I know its not more than that but the PO only had a receipt from mid 99' and the ODO had stopped.

Garth S

Hey Warren,
Have all the fingers crossed that only good news awaits you when you peer inside this weekend. If you could use a 'cyber hand', hit me with a PM ... better still, for a real hand, what's it like driving in the White Mountains this time of year?
Every MY has it's kinks: we did a friend's '86.5 TB/pump in my garage ~ a year ago - and it's still running !

UKKid35

Please please note that if the belt moves when you turn the engine (either by starter or by hand) this does NOT mean that the belt is OK. You have to check whether the TDC marks on both cams match the crank mark.

Even with many stripped teeth a belt will continue to move and turn cams, my engine even ran (for a second or so) after it originally died. I continued to live in hope that there was nothing major wrong because I had a spark and could see the belt moving through the cam cover inspection hole.

Thom1

Warren,

You can check the cam gear alignment/slippage by looking down through the upper front timing belt cover holes. Remove the air intake tubes. Look down through the cover holes with a flashlight. You can see where the notches on the back of the cam gears should line up with notches on the rear covers, at top dead center crankshaft position.

Warren928

I just tried seeing the timing marks by looking down the air vent holes on the covers. So far, all I could see was the front half of the sprocket and belt. The left belt side looks like it has a dull backside and the right side looks like the belt has moved an 1/8" toward toward the block. Yes, they look uneven on the sprocket....