Mk2a sore head ! and gasket problem

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Ken Graham

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Another winter looming and time for the head to come off again .Can anyone help ? when I bought my 850mk2a the head gasket was blown , I have had the head and barrells skimmed and rebuilt it twice and still can't get a 100% seal . the main problem area seems to be around the pushrod tubes ( could be wrong ) I hear people talk about models that had dowel type fittings ? which models were these fitted to . any info much appreciated.

Cheers Ken.
 
There has been a recent thread where a single strand of silk thread was used around the pushrod tunnels and the oil holes to seal these areas on a copper head gasket. The thread may have been coated with gasket goo too but the actual thread will tell you more.

More info here best-copper-gasket-sealant-t6441.html?hilit=head
 
1) The single most important thing is using a good crankcase brreather. That alone might cure the problem.

2) Use a flamering head gasket. Even when gooped and annealed the copper ones sometimes leak.

3) Torque the head correctly. Thse 2 front studs can't be brought to 30 ft-lbs with a small box wrench.
 
maylar said:
Thse 2 front studs can't be brought to 30 ft-lbs with a small box wrench.
Click to expand...

Those 2 front studs shouldn't be brought up to 30 ft lbs at all (max. 20 ft lbs). Overtightening these 5/16" nuts will result in a non reparable small crack into the pushrod tunnel which will cause oil leakage.
 
nortonspeed said:
maylar said:
Thse 2 front studs can't be brought to 30 ft-lbs with a small box wrench.
Click to expand...

Those 2 front studs shouldn't be brought up to 30 ft lbs at all (max. 20 ft lbs). Overtightening these 5/16" nuts will result in a non reparable small crack into the pushrod tunnel which will cause oil leakage.
Click to expand...

The two I'm referring to are 7 & 8 in the tightening sequence, and they're 3/8" studs. 30 ft lbs according to the book.
 
maylar said:
The two I'm referring to are 7 & 8 in the tightening sequence, and they're 3/8" studs. 30 ft lbs according to the book.
Click to expand...

Allright Maylar, so you were referring to the bottom 3/8" sleeve nuts and not to the top 5/16" nuts!
 
Thanks guys , I will pull the head and have a look : it is running on a copper head gasket right now may change that . I have A BRAND NEW set of barrells that I may prepare for the next rebuild.
Ever in Sunny Glasgow make sure to look in on Gambrino and ask for me.

Cheers Ken.
 
the great head gasket debate, much like motor oils, is always controversial. I would only ever use a solid copper one - but its essential that they are annealed properly - and thus the reason why some people have problems with them. You can also use jim schmidts excellent web page/suggestion to help combat leakage - ( following stolen from page)

"To prevent oil leaks, use your favorite sealer and lay a loop of silk thread or dental floss around the pushrod tunnels and the oil return hole – crossing over the ends of the string. Do this to the head - not the gasket"

http://users.gotsky.com/jimschmidt/nortonrods2.html

i thought Jim used to have a pic or two on his web site showing this, and you could probably email him for the pics should you need them

i find the flame rings blow out a little easier, but again 6 of one, half a dozen of the other
 
First step is make sure the head is flat. Usual problem is at the base of the studs where the stud can pull the surface up. Countersink the stud holes lightly and flat off on plate glass with grinding paste. Make sure any helicoils,if they're fitted, start at least a full turn clear of the gasket face, less than that and they will pull the head surface out of true.

Gaskets are just personal preference. I never had any success with the copper gasket on an 850, the factory obviously didn't think much of the copper one either, they never fitted it to an 850.

The eyeletted gasket I find works very well with the addition of a very thin smear of silicone around the pushrod tunnels.
A PCV reduces all engine leaks significantly, a worthwhile addition.
 
Ken,
Forget the dental floss, goo & any form of toothpaste etc.
Remove studs from head & barrel, apply grinding paste to head & barrel, & lap them together. You will then have a perfect mating surfaces. Then use an eyeletted gasket.
 
Even torque all around with a flame ring, but most importantly put some silicone sealer on the bottom of the front two top nuts! The front studs off often break into the push rod tunnels and wick up the treads! :wink:
 
I think I would agree with putting sealant on the threads & mating surfaces of the 2 front studs, can't remember if I did that.
It's an age thing.
 
Thanks again everyone.

And in Scotland "The nights are fair Drawing in" so I will have plenty of time to get to the bottom of this.

Cheers Ken.
 
Flo said:
I think I would agree with putting sealant on the threads & mating surfaces of the 2 front studs, can't remember if I did that.
It's an age thing.
Click to expand...

I thought I'd re-torque one more time after a couple weeks and the silicone had set. Immediately stated leaking! :? Removed nuts (not mine) and siliconed again. No more leaks.
 
Could someone specify which bolts are what torque by tightening sequence. I seem to get the torque mixed up whenever I do the head.
 
Ken
I recall that Mick Hemmings in his rebuild CD, stated that if a Commando persistently blows head gaskets or if you skim the head and barrels you should check that the bolts are not bottoming out. Some guys including myself use Triumph head washers because they are thicker than the Norton washers on the 5 top bolts. Try this check before you go at it with another flattening attempt. :wink:
CNN
 
Thanks once again , will check the length of the bolts and washer thickness ! hopefully I will get it correct third shout.

Cheers Ken.
 
Ken Graham said:
Another winter looming and time for the head to come off again .Can anyone help ? when I bought my 850mk2a the head gasket was blown , I have had the head and barrells skimmed and rebuilt it twice and still can't get a 100% seal . the main problem area seems to be around the pushrod tubes ( could be wrong ) I hear people talk about models that had dowel type fittings ? which models were these fitted to . any info much appreciated.

Cheers Ken.
Click to expand...

Hi Ken,

Check the intake valve cover for oil wetness from the one fixing cap nut downward. If this area is wet....Commando heads do a fun trick at speed where that oil gets pulled forward then sprays out from appearantly the push rod tube area. It drove me crazy replacing head gasket for a long time.
 
Got to agree with Ludwig, 'cept I loctite in the two studs that break out into the pushrod tunnels, and ensure all the bolts run finger tight through the head into the barrels. If not run a clearance drill through the offending holes. Then fit a composite gasket bone dry.

Works for me every time.

Cash
 
Gday Ludwig, your quote below

"They should at least be helicoiled or better , a bronze insert . AND made longer"

If this mod is done to the head, what torque then do you apply?
Would be also interested in any further information on this such as the size of the bronze insert etc.
Many thanks in advance
Foxy
 
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