Tightening order for cam caps and rocker assy?

[olr159w]

Hi

The pain continues unfortunately.

I got some new shims from Alun after a relaxed shipping effort from UK to Perth. I substituted the new shims and remeasured - everything was supposed to be 12 thou but I had a 14, two 13's and a sort of 10.5. Which IS odd because everytime I measure it something is "out" but I thought one last go as I had the necessaries. I was tightening it all back up and the last cam cap bolt I tightened kindly stripped the thread.

Again. So that's both the threads for the cap at the chain end. Which means now the head goes back to the engineering workshop for yet another helicoil.

I have been meticulous in the process. All threads checked out and cleaned, threads and dowels with a bit of copperease and then tightened down half a turn at a time in turn radiating from centre. Particularly after the first thread stripped and I am mindful that of course the cam doesn't sit in place as such so I've arranged the cam lobes to be considerate of not applying pressure solely at one end so to speak. Besides which the manuals say nothign about the sequenceanyway.

And yet here we are again. Is there something I'm doing wrong or is it just old age and the impact of steel bolts in alloy heads?

thks

[Philip Larmour]

In assume by "old age" you are referring to the cylinder head?? If so that is most likely the main cause of the stripped thread issue. You also need to consider, how many times have they been undone and retightened in the last 50 plus years?

Good practice to lay the cam in the head with as little load on the cam caps as possible when you are fitting the cam caps, and yes tighten them progressively I usually start with the cam cap with the least load and work towards the most loaded cam cap but only tightening slightly more than finger tight as i work along the cam.

Most of my heads have been helicoiled for all the cam cap bolts, and some of them have been race motor heads for the last 40 years.
Philip

[olr159w]

Ha ha ha ha yes I was referring to the cylinder head but it could just as likely apply to the owner.

Regarding your good practice advice below that is pretty much exactly what I am doing, although maybe with a caveat. I've tried to lay the cam with minimum load at either end on the basis that as the lobes in the middle are tightened down their greater load is at least shared across bolts on either side. And then finger tight initially followed by half a turn or so at a time working from the centre outwards.

It sounds like it is what it is although in consideration of the last 50 years I gotta say its a 1980 so that's 43 max plus the head hasn't been off in 20 years. So not that much wear and tear in principle.

The first one helicoiled was timing chain end upper cap bolt. The one that has gone now is the other bolt on the same bearing cap. I don't know if that could mean anything

My problem when I take it in is do I do just this one only to find that another fails when I reassemble? I've still got 12 to go.......

But not keen on pointless spending particularly given I should be at a place of one single reassemble with known shims when I get it back. So its the gamble I guess.

On another subject do you happen to have any of those cold air inlet boxes that SprintParts used to sell?

thanks for the advice

mark

[JerryTR5]

I feel your pain re stripped threads.
I helicoiled them all and replaced the bolts with studs which seemed to me to be a better engineering solution.
Jerry