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Head Face Barrel Damage

Submitted by martin_seymour on Tue, 05/09/2023
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Commando

I bought a grass track outfit for the engine and box - an 850 Commando that was running on Methonal

I've stripped the engine down and look what I found - a most unorthadox method of lowerering the compression ratio. There is evidence of other valve pockets being machined out but that couldn't have been enough. My problem is that the 'Builder' has caught the barrel/ gasket face with his die grinder (Angle grinder?). Can this be repaired or will it not matter?

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Submitted by george_farenden on Tue, 05/09/2023

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I would say yes it does matter.

At the combustion chamber edge is where the gasket is subject to the highest pressure and therefore most likely to fail.

If it were mine, I would give it a light skim off the top face, until flat all over.

And while you are doing that, make sure the head is still flat too. 

Either that, or make sure your vehicle recover membership is good.

Regards, 

George 

 

Submitted by martin_seymour on Wed, 13/09/2023

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Oh Bloody hell - the skirt is cracked also - it's been drilled but studying the picture the re's a mark going beyong the hole - but without depth? It's not eithin the ring sweep but it does stand proud.

Regarding the gasket face damage I was advised to counter bore the face to remove the damage and shrink in a 'ring' - the damage again not within the ring sweep.

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Submitted by george_farenden on Wed, 13/09/2023

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Hi Martin,

Seeing that, would it not be better to get a sleeve inserted instead? If a 'top hat' profile sleeve was used, it would cure the top face damage at the same time.

But knowing your luck, the crack will be on the other cylinder...

George 

Yes George I've come to that conclusion - but to do both and get them back to std. The RGM liners 'Top Hats' being 82mm in diameter wont clean up all of the damage - it could be brazed up first before boring out for the liners?

Hi Howard,   looks like a job by those fine craftsmen ‘Bodgit &Scarper’.

if the damage is less than 0.030” (0.75mm) machine that much off the top face and fit a 0.030” decompression plate under the bottom of the barrel.

At least he realised that to stop a crack propagating further yo drill a hole at the end. As it is below ring travel I wouldn’t worry about it, mine has had a much bigger crack and a piece knocked out when a con rod blew and it has performed admirably since. 

At least you have taken it to pieces and can get the grinding scarfed from the pistons and rings.

Best of luck

Dick Hudson  

 

Submitted by ashley_cutler1 on Fri, 15/09/2023

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Looks like odd non Norton pistons machined in more ways than to get them to fit. I know racers will modify extensively, but what it is in the photo is not something I would expect racers to do. It looks like a of box scrap that someone had has been hammered together and sold with the methanol race engine tale to sell it.  

The outfit has history but quite a few different owners. Yes the pistons do have multi cut outs for the valves until someone hit them with an angle grinder - it was suggested to me that this might of been done trackside - makes sense. In fack the piston don't look that old. Money and some skill had been spent on the head and gearbox.

Submitted by martin_seymour on Mon, 18/03/2024

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Ha - Found these on Fleabay - listed by everyones favourite dealer in Cannock for the 600/650's - you have to ask yourself why? Especially at their price!

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