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Discussion Starter #1 (Edited)
Hi folks,

Long story, had a few years trouble, head was leaking oil into the chamber, mixture lean. 1971 t120 motor.

Removed and reseated head with new head gasket and the proper large washer. Same story, sort of.


Redid it again over the winter real slow... checked head for straightness, etc etc... Had the seats machined flat where the large washes go...
Used new inner and outer head bolts as I found a little necking on one old one. Bolts were from TMS (recommended on this forum).

Torked head up, left for few days and torqued again, Ran it on a short ride for 15 minutes and torqued again. At this point most of the bolts had moved about 45 degrees from the very first torquing position (dab of white paint marking). Did tappets, etc.

I planned to retorque again after 250 miles.

But after I ran one tank of gas though (150 miles?) I heard a strange sound (like exhaust escaping) and so removed tank to inspect and retorque. I tried to loosen a quarter turn before torquing first bolt but realised there was no need as the bolts moved too easily.

I retorqued everything and found all bolts to be a little loose. The final position was now about 90 degrees for most of the bolts. I adjusted the tappets and found all to be tight, almost no clearance.

On top of that a close inspection shows that head gasket had blown and some gas was escaping from the side of the cylinder.





I'm starting to wonder if the head is not made of inferior material, or possibly was overheated and has weakened, I doubt it's the bolts as head has been problematic before.

I'm going to run after the retorque and see what happens. Either way I can probably not spend any more serious time on it until next winter so I've not got much choice but any ideas or advice greatly welcomed.

A bit depressed BMF....
 

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Anneal gasket.
Torque and set valve gaps
Heat cycle
Torque and set valve gaps
100 miles torque and valve gaps
500 miles torque and valve gaps
 

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Discussion Starter #4
Hi Guys, its been a long story, I used the big gun merc sealant (similar to locktite 518 I think).

Gasket was old but annealed, I torqued the head (and adjusted tappets) a few times more than you suggest Dave.

Would the new bolts be stretching, even after the first three torques and a short runnning period (45 degrees more turn to get to torque).

Im stumped, what would you folks do next?
 

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Hi BMF, I'm very sorry, I didn't realize you reused the old head gasket.

I know some anneal & reuse, but I don't like to do that, especially if the old gasket had any signs of leakage at all. I'm very sorry I didn't make it perfectly clear to get new gasket. As I recall the old head gasket was leaking.

I know you flattened the head which was certainly needed.

I've never annealed a new gasket. Some do, but I never have & have never had a problem with new gaskets not annealing.

But at this point, nothing to loose in retorquing & another long road test. You might get lucky.

I know it's not wise to skim a head unless it's really needed, but dips & high spots in head sealing surface demand skimming. These defects cannot be cured by head straightening. Depending on how much skimming is needed, a thicker head gasket is required.
Don
 

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Discussion Starter #6
No worries Don. I only had 500 miles on the new then Morgo gasket, so did not think twice about using it again (I've got the Morgo kit on, came with the engine way back when )
 

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The leaks at the head/cylinder joint has been discussed many times on Brit Bike...On the OIF engines it can be oil leaking from the rocker boxes down the head stud and then onto the head gasket...Cylinder compression pushes the oil past the head gasket...A solution is to seal the washers with RTV or use "sealing washers"....
I have reused the head gasket on by 650 race bike at least 5 times, annealing it each time...It does not leak...
 

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Discussion Starter #11 (Edited)
Hi Folks, thanks for all the input.

Bruce - I think he means "excessive crush " ;-)

Re other posts;
I tried reallly hard last time;
Head and barrels were flat....
large correct washers used on the inner head bolts and the bolts were sealed with high temp sealer, I did not find oil on the bolts as previously so hopefully that was cured...
Crush was 35 thou...
Used the merc sealant because the copper coat did not seem to work at all the previous time, but that time I did also seal the inner head bolt washers... maybe not enough.
Some say use spec torque or head will leak, others use 30% higher toque with success...

I'm going to have to think long and hard about all this....... Dont really know what else to do differently besides.

I'm starting to have a little sympathy now about the guys that ride their bikes even when it's not workign properly and risk blowing the whole thing up.... Not saying I will ever do that ;-)
 

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Hi Brett -

Insufficient or excessive crush could both concievably lead to an oil leak I suppose, but .035" is right in the middle of the recommended range so it's hard to understand how that could be the problem.

My bike's completely oil tight at the moment, EXCEPT for oil leaking from the exhaust rocker box cover. I'm carrying a rag around with me to mop up the spillage each time I gas up. Undergoing shoulder replacement in less than two weeks so I'll have plenty of time to replace the gasket during my recuperation.

I don't suppose your torque wrench could be too far out of calibration?

Try again with copper coat AND seal the bolts?
 

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Discussion Starter #14
I was thinking why the bolts were leaking oil even though Id siliconed them. Would retorquing not just break any seal as the bolts turn, breaking any seal on the top side or the bolts and washers turn, breaking any seal on the bottom side?
 

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Hermit47 - not insufficient crush but too much crush, meaning the head when installed on the barrels, with pushrods all assembled and all pushrod seals in place, and head gasket in place is still sitting too far off the barrel, so when its tightened down it pushes the bottom pushrod seal out of the wedding band and exerts an upward force on the fore/aft centreline of the head.
 

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I was thinking why the bolts were leaking oil even though Id siliconed them. Would retorquing not just break any seal as the bolts turn, breaking any seal on the top side or the bolts and washers turn, breaking any seal on the bottom side?
Silicon, would not use the stuff on anything other than exhaust flanges. Yes it will 'break away' when subjected to additional use as in re-torquing, and also breaks down into rubbery snot, blocking oil ways. As suggested, use copper coat on head-gasket and something like Stag Wellseal in other places, find it better than Yam-bond which tends to go a little to solid for future torquing/adjustment.

Hermit47 - not insufficient crush but too much crush, meaning the head when installed on the barrels, with pushrods all assembled and all pushrod seals in place, and head gasket in place is still sitting too far off the barrel, so when its tightened down it pushes the bottom pushrod seal out of the wedding band and exerts an upward force on the fore/aft centreline of the head.
Well said, simply put, the head is 'held off' no matter how much torque you use.
 

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Hermit47 - not insufficient crush but too much crush, meaning the head when installed on the barrels, with pushrods all assembled and all pushrod seals in place, and head gasket in place is still sitting too far off the barrel, so when its tightened down it pushes the bottom pushrod seal out of the wedding band and exerts an upward force on the fore/aft centreline of the head.
This is a prime culprit for the head gasket letting go between the cylinders, not so much on the outer areas.
 

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Hermit47 - not insufficient crush but too much crush, meaning the head when installed on the barrels, with pushrods all assembled and all pushrod seals in place, and head gasket in place is still sitting too far off the barrel, so when its tightened down it pushes the bottom pushrod seal out of the wedding band and exerts an upward force on the fore/aft centreline of the head.
Being left-handed, right-brained, and often out of my mind, I had to think about this quite a while before finally realizing that I was operating on a faulty definition of 'crush'.

I thought of 'crush' as the correct amount of free space between the loose head and cylinders to ensure that when the head is tightened down the PRT seals will be sufficiently compressed to be oil-tight. So using too-thick PRT seals would mean that there was insufficient 'crush'.

It finally occured to me that I needed to think more literally - to everyone else 'crush' is the correct amount of compression of the PRT seals, so using too-thick PRT seals would result in too little free space and therefore too much 'crush'.

(When I alternate between the two thoughts I find my mind wandering around inside an Escher drawing - try it!).

Sorry for any confusion I may have created in the minds of others.




tridentt150v said:
We call that a pocket gasket, guaranteed to fix all oil leaks!!!
Good one! And no sealant required!
 

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Discussion Starter #19
Super interesting article. Seems they are talking about Harleys and the torques are much higher than ours, but the interesting fact that the first torque defines how it will take torque in future and that over torquing is the main reason for head gasket failure.

Sneaking up slowly on the final torque also is important as Don indicated previously.

Article is here
 

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Super interesting article. Seems they are talking about Harleys and the torques are much higher than ours, but the interesting fact that the first torque defines how it will take torque in future and that over torquing is the main reason for head gasket failure.

Sneaking up slowly on the final torque also is important as Don indicated previously.

Article is here
I'd agree, good in depth analysis, one or two factors different as you point out, but universal application. The main point I draw from it is increasing torque above a certain point does not equate to better sealing. Happy days when expert opinion is available. :smile2:
 
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