TTY head bolts - replace?

Nope.

If the specs in the factory shop manual are something like "xx ft-lbs + yy degrees" the bolts should be replaced. In fact the FSM will probably tell you specifically to replace them.

If they are TTY, you might want to consider replacing them with ARP, which would be reusable. I'd prefer studs to bolts, makes positioning the gasket easier and they are theoretically more reliable.

nate

I would agree with replacement, due to lack of further information on their age or if they have been loosened in the past.

Why not? Depending on the application, he may be right.

Not true! Just because a bolt has a torque/turn value does not mean that it is a "torque to yield" bolt that needs to be replaced. Best to follow what the factory service manual says. I can't speak to other brands, but GM will always tell you whether a bolt has to be replaced or not. Trust me, not all torque/turn bolts have to be replaced.

Ian

TTY intentionally stretches the fastener to the point just before yield. Torque plus turn is many times considered to be more accurate for fastener stress and gasket compression. It also tends to ignore the effect of thread friction where a lube (if any) is not as specified resulting in more accurate setting. The method I had a dard time wrapping my head around was the Kanichi (spell?) wrench I saw being used to troque the head bolt on the B5.9L Cummins at the factory a few years ago. It uses a sonic sensor to determine when correct torque has been reach based on sound pitch. It apparently works just fine in practice.

Lugnut

I have seen adverts on bolt elongation gauges, but have never worked with one. They claim it is the 'only' way to fly.

Have you guys ever worked with one of these.

I had heard the same story as Nate, but good to know that there are exceptions to every rule.

One of our engineers also told me that if I install studs, as was mentioned earlier, that I would have to have the engine bored with studs in place and with a plate installed. I never heard this before, but would appreciate any comments.

I think it is the best of best if you can do the boring with a plate torqued down and with the engine heated to operating temperature, but I didnt really think there would be a difference between bolts and studs. ??

Use a torque wrench and the same old headbolts,if you want to. cuhulin

You are way out in the sticks,no access to new bolts.You think you will have any lesser luck with the same old bolts than new bolts? You will not. cuhulin

Many years ago,about once or twice each month,people used to remove the cylinder heads from their vehicles.They would scrape out the carbon,put on a new head gasket,use the same old head bolts and torque wrench or no torque wrench,tigten her down and keep on driving.All the new bolts in the World will not do you any better than good usable old head bolts. cuhulin

Ummmm.....the year is 2007.

Ian

Unless, of course, the torque spec is such that the bolt is permanently deformed by the act of torquing it down. Which can and does happen.

Back in the ancient days you describe, head bolts were simply good quality standard cap screws, and they were sized/torqued so that didn't happen. That is not always the case on a modern engine.

nate

There are many folks who do not realize that there is a difference between a "torque to yield" bolt and one that simply has a "torque/turn" spec for tightening it down.

On the other hand, it certainly would never hurt anything to replace head bolts when doing a repair job.

Since I've never been into performance applications, I don't have a definitive answer for this. I've always thought that bolts or studs notwithstanding, a performance machine shop would always bore cylinders with torque plates installed.

Ian

Yes you should use a torque plate on a performance engine with studs. The reason is that the bore will distort some when the studs are torqued down. So you heat the block and torque the studs down and then do the final honing. You also want to install the main caps since they can cause the bottom of the bore to move a bit as well. This goes along with all the other machine work done in order so you don't mess up the block.

BUT the above really only applies if your building for max performance. For a street engine you could install studs and call it close enough. TTY bolts are use once and replace. Torque+angle bolts MAY be able to be reused. If you can reach both ends of a bolt a stretch gauge is great, if your using a stud it is possible to use one but not easily.

Some time in my past, we used stretch guages on many of the fasteners in the locomotive engines. The mains were a 3" diameter stud about 20" long. We "snugged it up" at 1200 ft lb and then put the guage on to stretch the suckers another

0.030". The rods started at 900 ft/lb and stretched 0.060". It could be a bear getting them tight if your air pressure dropped under 250 psi at the wrench.

Lugnut

Nate Nagel wrote in news:erllh741vk8 @news2.newsguy.com:

I thought that was what "torque to yield" means.

The bolt is tightened just to the point where it's permanently stretched, which is why that sort of bolt needs to be replaced if removed.

In order for any word or phrase to have any meaning it needs to be used correctly. In this thread, the only thing that is known for sure is that the OP has failed to ask a meaningful question.

The question is - should the OP get new head bolts? What kind of engine is unknown. Someone might guess it is some kind of Nissan because a Nissan tech is said to have offered an opinion. But who knows, the Nissan tech might just be his neighbor and the engine in question might be a lawn tractor. Presumably the tech has told him that he doesn't have TTY bolts and yet the idiot asks a question about TTY bolts and asks if he should believe the tech (without actually knowing what the guy told him). So my take is - even if the "tech" is retarded and has an IQ of 40 and just sweeps the floor down at the Nissan dealership I would say the the tech is probably right simply because he has to be a little smarter than the guy asking the question.

-jim

You should do that even with BOLTS! No reputable engine builder would do otherwise.

I would say that there's not. And in fact I'd say studs would be less likely to distort the bore than bolts. But a "torque plate" with all the fasteners torqued down to the same value as the cylinder head will have is the ONLY way to go, regardless.

You certainly WILL... IF the old bolts were "torque to yield" or if they have been elongated/necked more than the manual allows. Not all head bolts are intended to be reused.

You are so FOS its simply amazing. Not even a Model T needs that frequent head-removal.

Sheesh.