Thread: Yet another head job!

Originally Posted by Leo109

Hi All,

Daphne Discovery has blotted her copy book again. The only 60,000 km old Turner Performance AMC head blew the gasket last week - very disappointing.

My friendly local head machiner (yes, I know your not supposed to, but I can't justify another new head) who says he's spent 20+ years building race engines, gave me the following tips:

* He says new bolts will always stretch slightly after repeated heat cycling and not maintain the required clamping force unless released and re- tightened after being in service for some time.
* Reuse the old bolts (that were new with the AMC head), as they've already had lots of thermal cycling.
* Thoroughly clean the block threads (and everything else too),
* Use proper engine bolt assembly lube, not just oil
* Follow the torque plus two/three stages of 'degree' tightening sequence, then
* Loosen all the bolts off and repeat the entire tightening sequence again, then
* yet again loosen all the bolts of and repeat the entire tightening sequence a third time!

He says I will be amazed how much further the bolts will turn between the first and third cycle.

So, esteemed spanner-wielding gurus - what do you think of this approach please?

All help much appreciated.

I can see this turning into a looooooooonnnnng thread

How much effort did you put in when you did the gasket last time (when putting on amc head)?

Originally Posted by Fausto79

How much effort did you put in when you did the gasket last time (when putting on amc head)?

Lots & lots. Everything very clean, including threads, and followed the prescribed tightening sequence to the letter...

Could you please provide more info and photos of what actually occured with the head/ head gasket ?
Did you retorque the head a week or two after instalation ?
What sort of head gasket did you have ?
Do the head bolts go through into the water jacket or are the holes blind ?
Did you lube under the bolt heads ?
Did you run a tap down into the block and clean the threads up ?


Ian
Bittern

That sucks Ian,, I feel your pain.

Originally Posted by Leo109

* He says new bolts will always stretch slightly after repeated heat cycling and not maintain the required clamping force unless released and re- tightened after being in service for some time.

Not on all engines and not with all bolts, I've never had to redo a tdi's head bolts yet

Originally Posted by Leo109

* Reuse the old bolts (that were new with the AMC head), as they've already had lots of thermal cycling.

yes, up to 5 times for the tdi300, I put new ones in if I Cant decipher how many times they have been used, if I can prove they've already been used 3 or more times. Its not because I dont trust them for use 3 and 4 rather to leave some "leeway" for an emergency situation for example if the owner is in the middle of no where can get a spare gasket but cant afford the money at the time for bolts as well

Originally Posted by Leo109

* Thoroughly clean the block threads (and everything else too),

Yes

Originally Posted by Leo109

* Use proper engine bolt assembly lube, not just oil

80/90 over engine oil, anything is better than nothing

Originally Posted by Leo109

* Follow the torque plus two/three stages of 'degree' tightening sequence, then

no, follow the sequence for the first torquing, do that again, and again now do the 3 stages of degrees, Smoothly for the whole turn in one movement, use paint pens, markers, indicators, scribes, digital overlays 6 people watching and counting and be stone cold sober for it. I've seen professionally built engines with one bolts marks not lined up IAW the rest of the bolts. you miss one step in the center 6 bolts on a tdi and you're begging for a blow through

Originally Posted by Leo109

* Loosen all the bolts off and repeat the entire tightening sequence again, then

NO. only do this if you think you have missed something and are still on the torquing stage, once you get into the +degrees stage the gasket and bolts are being compressed and stretched.

Originally Posted by Leo109

* yet again loosen all the bolts of and repeat the entire tightening sequence a third time!

again NO. only do this if you think you have missed something and are still on the torquing stage, once you get into the +degrees stage the gasket and bolts are being compressed and stretched.

Originally Posted by Blknight.aus

Not on all engines and not with all bolts, I've never had to redo a tdi's head bolts yet


yes, up to 5 times for the tdi300, I put new ones in if I Cant decipher how many times they have been used, if I can prove they've already been used 3 or more times. Its not because I dont trust them for use 3 and 4 rather to leave some "leeway" for an emergency situation for example if the owner is in the middle of no where can get a spare gasket but cant afford the money at the time for bolts as well


Yes


80/90 over engine oil, anything is better than nothing


no, follow the sequence for the first torquing, do that again, and again now do the 3 stages of degrees, Smoothly for the whole turn in one movement, use paint pens, markers, indicators, scribes, digital overlays 6 people watching and counting and be stone cold sober for it. I've seen professionally built engines with one bolts marks not lined up IAW the rest of the bolts. you miss one step in the center 6 bolts on a tdi and you're begging for a blow through


NO. only do this if you think you have missed something and are still on the torquing stage, once you get into the +degrees stage the gasket and bolts are being compressed and stretched.


again NO. only do this if you think you have missed something and are still on the torquing stage, once you get into the +degrees stage the gasket and bolts are being compressed and stretched.

Dave's answers here need to be made into a tutorial. Last time but one I was interrupted in the tightening down sequence due to a panic phone call from my mother's carer. I had no idea where I had got to. I went on memory, which is always flawed, but more so when stressed. Blew the gasket after maybe 25,000 ks. I got some different coloured markers next time and it works. Keeps you up with what you have done. $5 of pens. No brainer. They didn't teach me that when I was RAEME. I don't think they cared.

Which Daphne???