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Head gasket

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Head gasket

Postby Geoff K83 » Sat Sep 14, 2019 8:57 pm

Being a bit of a novice in this department is there an easy way of telling if the cylinder head gasket has blown
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Re: Head gasket

Postby Storkfoot » Sat Sep 14, 2019 9:12 pm

Usually you can see black sludge leaking from the outside. However, it can leak into the stud holes which won’t be visible from the outside.

If you can’t see externally, you’ll have to take the cylinder head off and then you can invariably see the leak.

What makes you think you have a leak?
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Re: Head gasket

Postby Geoff K83 » Sun Sep 15, 2019 11:59 am

Just had its MOT and was advised head gasket or a blow in the exhaust
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Re: Head gasket

Postby Storkfoot » Sun Sep 15, 2019 12:08 pm

Basically, you’ve been advised you have an air leak. They are the curse of all two strokes. Check cylinder base, cylinder head, where exhaust joins with cylinder and also carburettor manifold.

As I say, tell tale signs for the first 3 of those is black sludge.

How is the scooter running?
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Re: Head gasket

Postby MickYork » Sun Sep 15, 2019 12:55 pm

Probably not the easiest, if you're not too familiar with Lambrettas, but by far the best is a "leak-test".

This will show if you have a leak and hopefully with some soapy water you will be able to locate the leak.

Do a search on the forum as it is quite a popular subject and there's some good info' regarding how to do this.
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Re: Head gasket

Postby Geoff K83 » Sun Sep 15, 2019 3:22 pm

Runs ok bit of job getting it started . Pops and bangs a bit at first gets better once it's been running for a while .have had a look underneath some oil on the cowling near the exhaust manifold and on top of the silencer
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Re: Head gasket

Postby Storkfoot » Sun Sep 15, 2019 8:08 pm

Geoff K83 wrote:Runs ok bit of job getting it started . Pops and bangs a bit at first gets better once it's been running for a while .have had a look underneath some oil on the cowling near the exhaust manifold and on top of the silencer


Sounds very much like a leaking exhaust gasket. It needs sorting now as it’ll only get worse. Runner board off, exhaust off, rear shock absorber and cylinder cowling off. Then, I am guessing, you’ll see that there’s a visible leak where the exhaust manifold meets the U bend.

If that’s the case, take the U bend off and you’ll be able to see where it has been leaking. You’ll need a new gasket and to make certain that the mating face on U bend is perfectly flat.

Have you bought Sticky’s manual?
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Re: Head gasket

Postby Geoff K83 » Sun Sep 15, 2019 8:28 pm

Yes I have will give it a go thanks for your help and advice
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Re: Head gasket

Postby Fast n Furious » Fri Sep 20, 2019 3:16 pm

Whilst you have it stripped down this far, it would be prudent to pull the cylinder off and check the bore and piston/rings condition, especially if you are unfamiliar with the engines history.
Do a de-coke and replace the gaskets to suit the port timings and squish. New exhaust studs and nuts may also be needed? It's all in Sticky's bible.
Sometimes (but not always), if the HG has blown you can hear an audible squeak when you kick it over without the ignition on.
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