Small End Bush Worn Out?

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Halfwhelk
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Small End Bush Worn Out?

Post by Halfwhelk »

After sorting out the exhaust pipe, footrests etc (see various recent forum posts). I have been able to ride my '55 Model 18CS around in the nice weather today .
It makes a prominent tapping noise*. Now, with no previous experience of the marque, I dont know how rattly these engines are, but it sounds like a worn small end bush.
Before I go pulling the engine to bits and doubtless finding other things that need doing, am I likely to find a replacement small end bush? They seem to be out of stock in the AMOC shop.
Is a DIY bush a possibility (I have machine shop facilities).

The engine seems to run fine but is a little smokey. Am I likely to get stuck in mid-rebuild because a worn part is unobtainable?

What does the voice of experience say? Leave it and suffer the noise and oil leaks until something breaks properly or steam in and refurb the engine? Bear in mind that part of the reason for getting this bike is to have something to work on and a bit of a challenge. :headbang:

*The noise is like tapping the cylinder head with a small hammer. It is at piston, not valve frequency (I think). It is quieter under load and noisiest on the over-run just as the power comes off.
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cfaber
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Re: Small End Bush Worn Out?

Post by cfaber »

When you inspected the piston was there wear on the rear of it? Does it still fit your barrel? If you have the tooling to cut a new bush, seems like a no brainier.
Fix it until it's broken!

Otherwise how will
anything get done?
Halfwhelk
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Location: Kent UK

Re: Small End Bush Worn Out?

Post by Halfwhelk »

I haven't started to dismantle it yet. I don't want to go there if I can't replace the bush/piston/whatever. This question is based purely on the noise at the moment.
alanengineer
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Re: Small End Bush Worn Out?

Post by alanengineer »

Thats where going to your local owners club comes in really handy. It may be a long journey for some, but its a whole wealth of knowledge thats free. Take a tape recording of your noise with you.
Halfwhelk
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Re: Small End Bush Worn Out?

Post by Halfwhelk »

The plot thickens...
I just had to have the head off.
One of the head bolts was finger tight and there was no head gasket. There's no setup where you would not have a head gasket is there?
Looks like the exhaust valve has been touching the piston crown (just slightly) which may explain the noise.
Inside it all looks clean. No appreciable play in the conrod at either end and there are honing marks still visible on the bore.

Alan, looks like you are in the location of my local owners club (Kent). Is it well attended?
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clive
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Re: Small End Bush Worn Out?

Post by clive »

CS engines may have no head gasket.
clive
if it ain't broke don't fix
SPRIDDLER
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Re: Small End Bush Worn Out?

Post by SPRIDDLER »

Always happy to help but you can save a lot of doubt by taking time to familiarise yourself with the masses of original factory info in Christians Archive.
For example by referring to your parts list for the '55 model here....
http://archives.jampot.dk/book/Spares_l ... ingles.pdf

where no gasket is listed for the CS model...........
18CS head joint.JPG
Likewise your Owners Manual which refers to a gasket for the touring models only....
http://archives.jampot.dk/book/Owners_m ... ingles.pdf
18CS head no gasket.JPG
and the Competition supplement....
http://archives.jampot.dk/book/Owners_m ... ctions.pdf
18CS head joint supplement.JPG
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SPRIDDLER
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Re: Small End Bush Worn Out?

Post by SPRIDDLER »

Halfwhelk wrote:*The noise is like tapping the cylinder head with a small hammer.
Halfwhelk wrote:Looks like the exhaust valve has been touching the piston crown (just slightly) which may explain the noise.
Check that the zorst valve lifter mechanism or its cable aren't incorrectly adjusted, sticking, or cable too tight, allowing the zorst valve hold open a tad (e.g. contacting the piston) and/or causing contact between the internal valve lifter mechanism (tapping noise) and the rocker box above.
'There is a tide in the affairs of men
Which taken at the flood............'
Halfwhelk
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Re: Small End Bush Worn Out?

Post by Halfwhelk »

@ Spriddler. Thanks for the info. I didn't know this existed. I will study this.
However: The barrel appears to be non standard, being alloy with through studs. The upper mating surface looks a bit rough.
Should I get this flat? (surface plate and scraper? Flycutter in the mill?) or just add a head gasket.

Sorry for all the noob questions. This is all a rather steep learning curve.
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SPRIDDLER
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Re: Small End Bush Worn Out?

Post by SPRIDDLER »

Halfwhelk wrote:@ Spriddler. Thanks for the info. I didn't know this existed. I will study this.
It's easy for me as I've had many years to become acquainted with what's there ;)

The damage to the piston zorst cut-out looks recent to me as it doesn't have any carbon build-up, but in spite of that the piston looks perfectly useable. You ought to check that the valve stem isn't bent/sticking or the valve head damaged.
However: The barrel appears to be non standard, being alloy with through studs. The upper mating surface looks a bit rough.
Should I get this flat? (surface plate and scraper? Flycutter in the mill?) or just add a head gasket.
I wouldn't like to advise on that as I've no experience with CS gasket-less head joints.
Sorry for all the noob questions. This is all a rather steep learning curve.
Relax! We've all been there :beer:
'There is a tide in the affairs of men
Which taken at the flood............'
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