Thread locker on main & big-end bolts

[Graeme]

These bolts in the TDV6 engine are not retained and with bolts occasionally found loose, I'm very inclined to use a thread locker when replacing the bearings, possibly the medium strength Loctite 641. 641 is slow curing so should allow time for the tightening stages. A mechanic will be doing the job.
Any comments?

[350RRC]

These bolts in the TDV6 engine are not retained and with bolts occasionally found loose, I'm very inclined to use a thread locker when replacing the bearings, possibly the medium strength Loctite 641. 641 is slow curing so should allow time for the tightening stages. A mechanic will be doing the job.
Any comments?

Based on experience with a VW motor nearly 50 years ago, and expert guidance from my grandfather at the time, I've always thought that the spun bearing /oil starvation issue was being caused by 'loose' main bearing bolts.

I rememberVera's husband line boring a 3.0 to solve the result but he doesn't mention any cause.

First time I've seen this mentioned as an issue.

The question is really are they 'undoing' or actually stretching?

DL

[Graeme]

I've read of several reports where 1 or more TDV6 main cap bolts were found loose. I understood they were quite loose rather than a little loose after having stretched.
I haven't read that the main or big-end bolts are stretch bolts and at this stage there's no thought of using new bolts. According to one source the bolts can be reused twice, ie used 3 times, but it will be easy to check if the existing bolts have stretched, albeit causing a delay if new bolts are indeed required. I lined-up a used crankshaft bolt with a new one which showed that the used one had stretched considerably at about the middle.

Both main and big-ends used to be locked with a tab plate or in some cases the main bolts were wired, but not these engines.

[DiscoJeffster]

I’ve built Mitsubishi and Nissan engines, high power, and’s none of them had any fastenings to stop the main or con rod bolts from loosening. If they’re torqued they’re not budging.
If they’re loose on a LION engine I can only assume they were incorrectly torqued to start with or the bolts have been overstretched ?

[loanrangie]

I found a lot of the camshaft cap bolts loose when i did a minor rebuild of the top end, that could have been from the impact following the tensioner letting go or the fact that 10nm isn't enough so i'd be inclined to use a mild strength locker.

[Graeme]

Unfortunately I didn't think to check the camshaft cap bolt torque. I did fit the updated sprockets though.

I suspect that the only draw-back of using a low/medium strength retainer would be if there wasn't enough time to properly tighten the bolts before the retainer cured. If bolts are loosely refitted then retainer applied immediately prior to starting the tightening process then 30 minutes should be enough time providing the mechanic doesn't get interrupted.

[Blknight.aus]

couple of things about loctite.

preps gotta be good dust rust and oil free..

if you're slow and shear the loctite once its started to set up you may as well have not put it on

if you dont use enough you may as well have not put it on.

if you use too much, 1. it can get places you dont want it, remember it doesnt set untill its removed from oxygen, 2. it can drop the run on torque sufficiently in some applications that you overtighten the fixing.

most of them break down with heat

not all of them retain adhesion in the presence of oil.

[DiscoJeffster]

It would be the torque impact I’d be concerned about. Nearly all torque values are dry torque so adding a fluid in there may mean over torquing is a risk. That said, if the bolts are angle finished (angle gauge final tightening) then that’s designed to compensate somewhat for variances in torque. Personally I wouldn’t do it.

[Graeme]

Total angle after torquing is 90 degrees so a slight change in thread resistance is likely to have negligible effect. However checking 641's specs, at 150 degC it has less than 50% strength and looses strength over time which is a bigger issue, so maybe nothing much to be gained.

[Eric SDV6SE]

Total angle after torquing is 90 degrees so a slight change in thread resistance is likely to have negligible effect. However checking 641's specs, at 150 degC it has less than 50% strength and looses strength over time which is a bigger issue, so maybe nothing much to be gained.

The 90deg after setting the specified torque is what achieves the required preload, and means the bolts are single use, they are most likely at or around 90% of yield strength.

I agree, not something I would do or much to be gained. Using quality bolts, clean threads, and sticking to the specifications would be the go