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Mk3 cylinder head gasket

Submitted by john_cowie on Sat, 18/12/2010
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Commando

My 850 Commando Mk 111 engine has been rebuilt very recently, she has 15 miles on the clock since the rebuild, looks like the cylinder head gasket is leaking, I believe it has been fitted with a copper gasket! Is there any way of checking without removing the head?

I have been advised to replace it with a standard gasket. Where would the best place to buy one? Part number etc please.

I looked in the Norvil site and could not see a 'standard gasket'

Many thanks

Jake.

Submitted by nicholas_marshall on Sat, 18/12/2010

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This is just my opinion but i would use a composite gasket with a light smear of silocone where the push rod tunnel is,with composite type gasket sometimes they weep oil for the first few hundred miles before they heal up,any Norton dealer should have these in stock regards nick

Submitted by tony_ripley on Sat, 18/12/2010

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Hi Jake,

I have had a MkIII since new in 1977 and it has about 60k on the clock. I have used both copper and composite and found no really difference between them. key points with copper gasket:-

Did you anneal it before fitting ? heat to cherry red and either allow to cool or quench, makes no difference but I prefer to quench as a gasket at 200 degrees looks the same as a cold one ! Copper work hardens, annealing softens it.

Did you use any gasket goo ? I tend to use Blue Hylomar but each to their own.

Did you torque it down in the sequence described in the manual ?

Are you sure it is the head gasket that is leaking ? If you have clean oil in the bike it can be very difficult to see the little leak coming down from the rocker covers until it is blown back by the wind.

If the head and barrel are flat, the nuts and bolts are clean (dirt/ damaged nuts and bolts will lie about how tight they really are), the gasket is annealed and the fixings as tight as they should be then a copper gasket will do the job as well as a composite.

Really the same rules, other that the annealing, apply with a composite gasket.

Do 50 miles and torque it down again.

Tony

Submitted by john_cowie on Thu, 20/01/2011

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Gents thank for the info, I initially thought the leak was from the tacho drive seal, discounted that by covering the front of the engine with talcum powder and taking her for a wee run, on stopping, the powder around the tacho drive was dry, could not see much on the engine as it had been blown back, there was quite a bit on the isolastics though, have not checked the rocker covers yet (currently offshore, when I was at home for Xmas there was no way I was taking her out in that weather).

Next step - Rocker cover check - Make sure bolts are torqued up to - ????????

I have ordered a composite gasket just in case.

Home end Feb, hopefully the ice has melted.

Thanks again

Jake.

Attachments Leak.jpg

Submitted by john_cowie on Thu, 20/01/2011

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Added a few pics, one above shows oil on the Isolastics, rocker cover looks clean, this pic shows clean oil beside the tacho drive.

Jake.

Attachments Head.jpg

Submitted by hans_taylor on Mon, 31/01/2011

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Jake,

Just a thought, if oil is on the iso casing at the front thats a long way down from the rocker covers ! There would be oil all over the place. Is it possible that some is coming from the cylinder base joint ?

If you must check the rocker covers, first check that they are perfectly flat, rub round and round on a ceramic tile or glass with grinding compound. Then , using a drill bit by hand, countersink the underside of the stud holes in the covers. 8mm drill would suffice. this will ensure that they sit flat on the head. Try them without gasket first.

looks a nice bike otherwise!!

Regards HT

Submitted by keith_glassborow on Tue, 01/02/2011

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Does look like base gasket. Did you rebuild or someone else? Base needs some kind of gasket goo (Hylomar or very thin smear of silicone). I know people do use the base gasket dry but it doesn't hurt to have extra security here just as long as you don't overdo the sealant application. Alternatively the case halves may be leaking, they also need a little sealant help.

Submitted by john_cowie on Wed, 02/02/2011

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Previously wrote:

Jake,

Just a thought, if oil is on the iso casing at the front thats a long way down from the rocker covers ! There would be oil all over the place. Is it possible that some is coming from the cylinder base joint ?

If you must check the rocker covers, first check that they are perfectly flat, rub round and round on a ceramic tile or glass with grinding compound. Then , using a drill bit by hand, countersink the underside of the stud holes in the covers. 8mm drill would suffice. this will ensure that they sit flat on the head. Try them without gasket first.

looks a nice bike otherwise!!

Regards

Thanks Hans will give it a go.

Jake

Submitted by john_cowie on Sat, 12/03/2011

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Update on work done:

A very big thank you to a Member of the Edinburgh branch ( I will mention your name if you want John) who has taken the time to show me how to remove the head (All bolts were loose) Head face was very porous, hairline crack between fins 3 and 4 front RH side! Basic check to see if the crack was the cause of the leak - unsure - (Thinking loose bolts at this time), fitted a new gasket and put it all back together again. Started her back up, lo and behold head still leaking.

I am not paying 1400 quid for a new head so have bought an old one for a couple of hundred, needs lots of work.

Back to sea shortly - will keep y'all updated when I get the old head sorted out and fitted.

Jake

 


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