Re-torquing head bolts and gaskets...

I once saw a gen3 with a blown gasket that had a loose head bolt. It happens.

 

Thanks for starting this thread!

I've had this conversation with several mechanics and wouldn't it be cool if someone with the most minor of head gasket issue in there Gen3 Prius at least temporarily address coolant loss with this method?

Sure hope this thread has legs... Maybe @Elektroingenieur has some thoughts on this subject?

And what do you think @ChapmanF ?

 

Good question! I've wondered whether that would reduce the risk of gasket failure, or at least delay it. Do we have an appropriate torque specification?

 

Well my dad had MG's from 1954 or so up through about 75. And those British Leyland engines I think it was the 1.5 I'm sure there are others were known for head gasket leakage I have seen people take strands of copper wire and wind them through the head gasket studs to help seal the head gasket of course this is all old technology way back in the day. Then gaskets like fel-Pro came along that were supposed to eliminate the retoring and hold the torque some of this worked on the British Leyland stuff so I'm not It was a crapshoot.

 

When I toured the 13 persona engine apart there was no loose head gasket balls they all seem like they were loctited down The bolts don't look bad once they were removed even removing them without the proper socket just to get them out I was going to throw them away I think I did actually I just wanted to pull it apart and see my head is fine and it's attachment was okay It just started to seep I think across one and two

 

This is what almost invariably shows in head gasket pictures. Not sure retorque would reseal that zone.

how to retorque btw: loosen them all off and retighten? To get there you’ve done virtually everything anyway; keep going?

 

Is there some locking feature that keeps head bolts tight? Unless they are unscrewing, I don't think there's a need to re-torque. I would also think that a multilayer steel headgasket would also make that unnecessary as well.

 

Just looked it up: they’re multiple, embossed steel layers, and the outer, black layer is “Viton rubber”. That outer layer gives it some compressibility, and presumably is what you see missing in places, on the failed gaskets.

 

Mendel, don't you have the the instructions for torquing the heads on a Prius engine?

Imho, in general, retorquing head bolts on aluminum engines with aluminum heads, wouldn't make any sense.
Bolt stretch is now used for newer designs.

Most aluminum engines with aluminum heads will have the head bolts torqued to 1-3 torque values (in sequence), and the final step is to do a a final tightening by angle.
This is done to better ensure the correct amount of bolt stretch. Bolt stretch can be more complicated, because of the the different alloys used in the aluminum head bolts, and various bolt/assembly characteristics.


For cast iron blocks and heads, and the technology level at the time, simple torque specs were often used.

Plus, all newer engines have multi-layer head gaskets (since ~80's).
The headgaskets used previously were often single layer, and had a number of limitations in trying to seal a head to a block, when the two items would be expanding/contracting at different rates (different thermal masses, and different cooling methods).

 

Yes I do. Off top of my head, it's 35 ft/lbs first time round, then 90 degrees, then 45 degrees.

 

I think there might be a reason we're not doing this. Anytime you're removing/adjusting bolts in an engine you risk running into problems, like one of them snapping in half! (Which always turns a simple job into a huge nightmare.)
Sometimes, "if it ain't broke, don't fix it" applies.

 

Yes, I would be cautious about this approach, with these new styles of head bolts that are torqued close to their yield points. This makes them longer and skinnier, and when you have the head off, you either use all new bolts, or you carefully measure how long and how skinny the old ones got, to see which ones can be reused.

To simply retorque them seems too simplistic for that kind of application. Taking them all out and checking which ones to reuse might work, but would have to be done in all the multiple loosening and tightening stages you'd go through in a head job, and that sounds like too much to get into in the name of prevention.

 

Loosening them before tightening them doesn't make sense to me... I think adding just under a 1/16th of a turn on each bolt to confirm they are tight would be worth a shot if you're in the earliest stages of coolant loss...

 

I remember back in the days of old British Leyland stuff '50s early '60s The 1.6 l I believe guys used to wind pieces of copper wire in between head studs . Trying to create seal needed. Modern gasketry . And special cut threads on head Bolts are supposed to negate this somewhat.

 

Yes, but checking the torque of all the bolts, as well 10ish degrees tighter might be a valuable step for Gen3 Engines at the first stage of coolant loss might buy some time, which is the point of discussion on this thread... As in if it's already broke...

 

Maybe so, if you're desperate.
As I already hinted, there's no official retorque specification, as far as I know, because the official procedure is tightening by angle. How much torque is typically required to perform the torque-to-angle method?
Instead of tightening all of them by 10°, my idea would be to go through the tightening sequence repeatedly with increasing torque levels, in small increments, starting low. Upon reaching a torque level at which at least one bolt turns slightly, STOP.

 

That'd be a better way to do it... Of course the sequence is yet to be clear... Seems like searching for tightening sequence for Toyota 4-banger in general is way to go? Maybe @SFO has the PDF on head bolt tightening?

 

I might should have checked the JDM engine I got just for haha's but I don't know if this is ever worked or what have you I've seen people do this on older stuff like back in the '70s and early '80s then the fancy threads started getting cut and head bolts permanent torque gaskets for flooding the market etc so it seemed a thing that was certainly being minimized and production vehicles what they did on high-end builds for racing and rallying. Was a bit different even then.