Premature TC failure Dropped In For Reference
Question We replaced the timing chain in an 86 22R, this included a head gasket set. After 1407 miles the chain snapped. Recommendations Suggestions?
Answered by EB
I have a dab of experience with timing chains on these engines, and have searched the world for the best suppliers. Quite simply, there are none that I would not consider using, and some I would prefer.
Unless there was a defect, (A possible scenario with any supplier) then something likely went wrong to cause the chain to snap.
*Look carefully at the gears, and at the passenger side guiderail and tensioner pad faceing for excess wear. If you see excess wear on every other tooth, the tensioner was not operating properly for some reason. This also shows as wear on the pads and guiderail.
We supply right at 100 timing sets every three weeks for the 22R/RE engines, we use M66 chains and they test to as good as any made. I know this for a fact because I was in the factory and sat in on some load/reversion tests, quite simply I can pick the entire front end of your vehicle off the ground with an M66 chain, in a pinch even tow it home.
But then we can do exactly the same with the Tsubakimoto, OSK (branded) the GCI, Sealed Power, Federal, on and on, all within 2% of test specs. The fun part is the Dual roller chain, which some love for it's "added" strength, fails at EXACTLY the same pull loads.
Yet we still see 1% fail, and normally early after an install. The chain WILL break if sideloaded, or if it is striking somewhere it should not be due to slack.
I would suggest you check to see if the oil pump mounting bolts got mixed up during install. If so, any long bolt will restrict the tensioner pad, interfere with it's operation. The result will be noise at best, and chain/guiderails/tensioner failure quickly, with the chain finally breaking.
*Now the bad part: Very likely, even at idle, you will have bent some or all of the valves. Replacing the timing kit won't fix this, the head will need to come off unless you are very lucky to fix the bent valves. Hopefully the timing cover won't be damaged, but if it is, you must replace that also.*EB
Inspection Results
We found 5 broken teeth on the lower gear; no marks on oil pump-drive and timing cover had a couple of scratches. Both plastic chain guides in mint condition, and best of all, not a single mark on the piston tops or valve bottoms.
This one-this must have been one of those in the 1% or less range- the chain must have been defective as upon inspection the link seemed to have stretched in the area where the pins tie it to the next link, all except one tiny piece of the chain were in place?
Reply Possibility
Now I know what did happen, and this is one sure way to break a chain. The key here is the "broken teeth" on the lower gear. Now this is a little bit of "Which came first, the Chicken or the Egg?".
We know that there is enough force in one single power cycle to actually move the entire vehicle down the highway at speed. We know that the instant the chain breaks, there is no more power.
Therefore the gear broke first, the tooth rolled over, the chain now has to reach around an impossible distance and gets loaded at and angle at the same time. The weakest link (where the hole for the pin goes in the side link usually) lets go.
Diagnosis is not a defective chain, it is a defective lower gear.
The lower gear is a casting, it needs to be for rigidity. This type of gear is then heat treated to harden it for wear characteristics.
So: Someone missed on the heat treat and got it too brittle..(I happen to KNOW this happens) or...someone putting in on felt it hang up a bit on the crank key and "helped" it into place with a handy hammer (the tiniest burr on a gear tooth is a guaranteed chain failure). Or...the warehouse person who is packing the kits dropped it on the concrete floor, then picked it up and stuck it in your kit.
I would hazard a guess the gear failed first....*EB
Last edited by kewlynx; 04/02/06 09:36 AM.
