Blowing Head gasket

Hi Paul, are you sure its coming out of the head gasket, the primary drive and your left boot seem too low down for it to be the head. Head gaskets usually manifest in oil on the side panels or air filter box. You can usually see where they have blown because there will be oil coming out of the join between head and cylinder block. Also they sometimes make a "chuffing" noise as that cylinder compresses.

Cheers Big Alan Clarke, Shenstone Branch Sec.

I had a massive leak from the cylinder head this TT turned out to be the breather blocked pressurising the engine leaked from the 3rd fin up. 2 cures unblocked the breather it's now a chain oiler, and fitted a Jeep pcv from Ebay. A Yamaha XS650 pcv can also be fitted.

Hi there Paul

I have a '72 Roadster as well. Some questions and observations:

A solution may depend on where the cylinder head is leaking from. Can you locate the point of leakage?

It's worth using Wellseal around the pushrod tube holes if they are the problem.

In my experience re-tightening of cylinder head nuts and bolts relates more to heat cycles than mileage.

My Roadster has hardly moved over the last 6 months since refitting the cylinder head but after just 3 heat cycles, whilst setting timing etc, the head needed re-torquing.

Have you looked at the NOC Technical Section on alternative tightening sequences?

I'd stick with the standard composite gasket as from what I've read copper gaskets have a whole other set of challenges!

Hope this helps and I'll keep an eye on this thread.

Regards, Andy

I use a copper head gasket no problems just anneal it before reuse and give it a smear of silicone around the push rod tube holes

hello I have just done a friends g15 matchless and he sent a atlas gasket setfor the rebuild which had a copper head gasket, the bike needed a re bore which we got out at plus 80, I removed a eyeleted head gasket on strip down, fair bit of work as the left piston rings were broke and a valve spring outer spring ! the bike ran but had piston slap, I put the head back on without annealing the new gasket tightened down and fired the bike up, all good warmed it up then rechecked the head but it was tight, problems sealing the rocker feed top allen bolts as I removed perished rubber washers on strip and tried copper but could not seal them, different oil feed block towers on the matchless?he ordered a commando oil line that solved that I rode the bike back to his but the first time out for him it blew oil out on the back of the right side on thehead gasket. tried a nip but it will not seal.

I wondered if the new gasket was old stock and would it have age hardened the copper and should have been annealed even for the first time,, fed up of course as its coming back and will need the head off which is a engine out of frame job, or has anybody dropped the front engine plates off and removed all studs bar one so the head clears the top frame rail? can it be done that way?

poor design altogether with all the spacers etc on the frame and footrests just to get the primary off. arthur.

Firstly Paul apologies, you are correct I noticed your head gasket problems and confused it with a question rolling around in my head re copper gaskets on a atlas, not even a commando, its when you considered using a copper one, my old 850 commando had always the composite and never leaked but it was a new gasket each time I did some work , sorry again for barging in on your thread, Arthur.

Paul

Alternative tightening methods are shown here: http://www.nortonownersclub.org/support/technical-support-commando Look under Cylinder Head & Barrel.

Are you sure that none of the studs have pulled from their threads or that the nuts aren't 'bottoming out' without tightening the head? I'm thinking particularly about the possibility of the downward pointing stud at tightening position 7 not tightening correctly.

A couple of things to try.

Andy

I rebuilt my 750 last year. Tried 3 new composite head gaskets & none of them would seal. They were from Mick Hemmings & Andover Norton. I have never had this problem before, having rebuilt many bikes over the years. I came to the conclusion that the latest batch were just no good, so I put a copper one in. Been working fine ever since.

There is an interesting thread on the accessnorton forum from Jim Comstock (comnoz) about head gasket leaks where he deduces that the head is compressing under pressure from the bolts. His fix is to slim down the bolts with a directional machining process (to avoid stress raisers) and allow the bolts to stretch to maintain pressure on the head. Most modern engines employ a similar waisted bolt design.

You may look at whether the front two studs have broken through into the pushrod tunnels to allow oil up through the studs. Also, weeping rocker feed banjo bolts somehow send oil forward to appear close to the front of the head gasket area

In another thread (The problem with surfacing a head on a plate) Jim is sceptical of lapping cylinder heads on a glass plate and shows a head that looks good but still hasn't cleaned up after a 0.005" skim.

That thread is about 4 pages back on the accessnorton forum. worth a look

my twopenneth, bearing in mind I know little of any Norton engine- many years ago my Atlas engined commando having been rebuilt by a professional team, blew both sides of the head gasket on it's way to the MOT station, no matter didn't need engine for mot so it passed, however replacement gasket did not help and it finally proved to be a problem with worn threads in the barrel not allowing the head bolts to torque correctly, my chum helicoiled these threads and used caphead bolts, [metric I think!] as a replacement, subsequently, when it was in use seemed to be quite successful

kind regards

Previously paul_smith wrote:

Hi all,

My '72 Roadster Combat engine Commando suffers from the head gasket leaking.

I replaced it a while ago and did a long ride then it leaked again (spots of oil over the LH primary drive cover and my LH boot) - replaced again with the same composite gasket with sealant this time - just the same on the first ride out.

I re-torqued after 100 miles - or best you can on several of the nuts!

I had previously flattened the head (glass and grinding paste) after removing the studs and checked the top of the barrel with a straight edge and torch - looked OK.

Should I go for a copper gasket?

I know lots been written about the gasket on the Commando - and I've read most of it - does not seem to help my bike!

Any ideas?

Thanks and regards - Paul.

Hi Paul,

Over the years of maintenance the mouths of the head bolts and stud holes will have probably burred over reducing the hole clearance. This can vary the friction of each fastener and though the torque down will perfect the actual clamping force won't.

Try fitting the head without gasket and pushrods to check that all the fastenings run fully down freely finger tight. If not you may have to run a standard size clearance drill through each hole not forgetting to remove the sharp edge.

After a head gasket change I usually run the motor up to temp let it cool and check the torque. Take the bike out for 10 to 20 miles let it cool then re-torque. If there's movement I check again after 50 miles.

I hope this is of help?

Dave

I agree with Dave. Put the head on without gasket and check the gap. It's surprising what you may find.

I use an eyelet gasket on my Commando but a copper one on my ES2. And I use none on my pre war ES2.

Some tine ago I had all sorts of problems with the head gasket on my Harley shovelhead. There are loads of different types available for these bikes. Eyeleted jobbies worked well on stoke bores, unfortunately I had 5 3/8 big bores. there were no eyeletted types available for these only stock type material ones. They were gobbled up in no time. Eventually I used some copper ones annealedwith sealant around the oil holes. Result.

If there is a problem with only a leak on the left side, why not ride side saddle????

I agree with Dave. Put the head on without gasket and check the gap. It's surprising what you may find.

I use an eyelet gasket on my Commando but a copper one on my ES2. And I use none on my pre war ES2.

Some tine ago I had all sorts of problems with the head gasket on my Harley shovelhead. There are loads of different types available for these bikes. Eyeleted jobbies worked well on stoke bores, unfortunately I had 5 3/8 big bores. there were no eyeletted types available for these only stock type material ones. They were gobbled up in no time. Eventually I used some copper ones annealedwith sealant around the oil holes. Result.

If there is a problem with only a leak on the left side, why not ride side saddle????