Re-torque head gasket from 56 ft./lb. to 75 ft./lb. (Good idea or bad idea)
 

I have a low mileage 1989 Supra Turbo (original owner) with a 7M-GTE engine. Everything about this engine is stock. Five-years ago, it was diagnosed with a blown head gasket and I had my local mechanic do the repair.

The brand of gasket used was Felpro head gasket repair “set” model #HS9473PT. Evidently my mechanic didn’t go the stud route but he did install new bolts (don’t know if they’re Toyota OEM or something else).

I came across an Internet discussion concerning this subject and just learned that head gasket failure is very common this engine. Evidently, the Toyota factory torque spec of 56 ft./lb. is inadequate to the job and eventually leads to failure.

As this was an expensive repair, I don’t want to go through this again. I discussed this with my mechanic and, after checking his reference materials, determined the spec he used was the Toyota specified 56 ft./lb.

I checked the current state of this repair using a Uview Combustion Leak Tester http://www.uview.com/ProductDetail.p...tNumber=560000 and, based on this test, there aren’t any leaks. So everything appears to be good for now. But I’m wondering if it makes sense to have him re-torque these bolts? From what I’ve been able to figure out, those in the know torque the bolts to around 75 ft./lb. when installing a new head gasket.

Again, it’s been about 5-years since this work was done and I’ve put about 10,000 “easy” miles on the car since then (current mileage is 53,000). The charge for doing this is minimal (about $200) which is substantially less than what I paid to replace the head gasket, machine the head, etc. (that job was over $2,000).

He’s a good mechanic whom I trust with all my vehicles, but he’s not a Supra fanatic. If he were to do this work, I’m confident he would follow a stepwise process (i.e., progressively tighten these bolts and not all at once).

I thought someone here might be able to clue me is as to potential pitfalls. Bottom line, is this a bad idea? Will I end up doing more harm than good?

Thanks in advance for informed advice!

its been done alot before with good results. as long as ur gasket doesnt leak right now then it should be good. dont loosen them just tq them down in id say two increments to 75lb ft and live worry free.

as for 200 bux for a retorque...thats a bit steep to me. seems a lil ridiculous to charge that much when all you have to take off is the intake tube (3000 pipe?) and the cam covers.

idk, id say its extra insurance and if hes as good a mechanic as you say, then it shouldnt be a problem.

It's roulette.... the upside is that it's roulette with an 18 shot revolver. There always exists the possibility that a jacket's hardened, got brittle and may be crushed or cracked when you increase the pressure.

The head bolts should have been retorqued at about 1-2K mi... There's some argument about this not being needed when reusing fasteners, but it's cheap insurance (especially with composite type HG's which squish more than MHG). As you're only sitting at 10K I'd be pretty confident about it, but ONLY if I knew everything in the initial job was done dead right (including chasing the threads in the block; VERY important). The critical factors are getting an even torque--> MUCH harder than most people think; Especially on an engine which has been heat cycled a number of times.

Do keep in mind, the average factory HG lasted over 100K miles and 10+ years.... if done right and the engine's stock the replacement should last as long.

I've detailed my usual routine for retorquing here before; A search should turn it up... try searching "striction" and "retorque".



(I'm not doing very good taking time out from here.... My wife may be right about the addiction thing and counseling MAY indeed be in order.)

Thanks guys -- this is excellent stuff!
 

I have a few things to confirm with my mechanic. He's a good guy and I'd expect he did things the right way (i.e., chased the threads, used a quality moly grease, etc).

It's probably apparent I'm not a professional mechanic. Your feedback has given me a few things to think about when working on my motorcycles. Hadn't really considered the effects of thread contaminants and lubricants on torque settings. I've always been pretty picky about "doing it right" and use a high quality calibrated torque wrench with whatever I'm reassembling. But I've probably been fooling myself because I've not factored in these variables. Always good to learn something new.

Thanks again!

You'd be amazed what gets skipped or missed in a busy shop.... I've never failed to be surprised on a fairly regular basis. Not that I suspect he did anything wrong... just a reminder that mistakes happen.

Sadly a lot of people are blissfully ignorant of the fact that even the most expensive, meticulously cared for and serviced tools may function FAR worse than the cheapest tools if you don't know how to use them. ;)

Good luck with everything!