Pushrod tubes

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Rob Harknett
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Re: Pushrod tubes

Post by Rob Harknett »

013843 that's the same number pictured on Clives barrel. Very odd it was used on 1950 and 1951 AJS but not on 50/ 51 Matchless. So you know what barrel you have got and what it fits. Your parts list will tell you the barrel you want ( check what size bore you want std + .020 or what ever. There may be some one who will swap. Try an advert .
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clive
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Re: Pushrod tubes

Post by clive »

Why odd? The 50/51 Matchless would have the mag behind the barrel so different to forward mounted AJS barrel.
clive
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Rob Harknett
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Re: Pushrod tubes

Post by Rob Harknett »

never thought of that Clive
MikeM.
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Re: Pushrod tubes

Post by MikeM. »

It is possible to mix and match various years on AMC parts, my Twingle has '59 crankcases and when I put it togetherin 1978 i had an up to '52 barrel and a '51 head, the barrel was rebored and adored piston fitted and lasted 60K miles until I put a hole in it due to too far advanced ignition retiming. with regards to the push rod tubes I didn't know there were different lengths and wondered why i had such a problem with tightening the head down!
The next time I took the head off I found that the tops of the tubes had been crushed in due to the rubber gaskets being compressed too much. With new tubes I trimmed about an 1/8" off of the top rubber gaskets and this seemed to cure my problem. Maybe thiAdam, just a thought.
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Re: Pushrod tubes

Post by MikeM. »

Sorry poxy computer has a mind of it's own,
Last sentence should read: Maybe this could help Adam, just a thought.
adz25
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Re: Pushrod tubes

Post by adz25 »

Thank you guys.

So i may get myself a decompression plate and trim a little off the top rubber rings to get it to work.

Mike, Did you ever have trouble with the pushrod tubes leaking with less rubber at the top?

I may well add a wanted/swap advert, but its a relined cylinder freshly bored to std, which would be difficult to find without having to reline and rebore at a fair cost these days.

Many thanks, adam
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Re: Pushrod tubes

Post by SPRIDDLER »

adz25 wrote:So i may get myself a decompression plate and trim a little off the top rubber rings to get it to work.
I and several others use nitrile 'O' rings which you can stack to the required height. These nitrile rings don't go hard and brittle (and then leak) from the heat like the pattern 'rubber' ones. The nitrile ref number is BS210 Nitrile. Dims are: 3.53mm section, 18.64 bore and 25.7 O.D. readily available but I bought mine from 'Simply Bearings'. I bought a pack of 50 at £6.24 (just 2 off cost £3.69!) and have given the rest away.
https://simplybearings.co.uk/shop?gclid ... gJg-fD_BwE

I prefer them to the NOS rubbers shown in the photo (at 5p each!) which I had in stock so changed to the nitrile rings which have been perfect for ten thousand miles..........
You still use the steel washers although I hadn't fitted them for the photo.
Pushrod 'O' rings seal (640x480).jpg
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bjorn
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Re: Pushrod tubes

Post by bjorn »

I believe the standard G80 piston was flat topped and did not extend above the height of the bore. From looking at the picture of your piston at TDC it will give a higher compression than the standard of about 7.3:1.

I am not saying that you do not need a compression plate, but if it were my engine I would do some checks and measurements first:
Loosely fit the head and push rod tubes to the barrel without any of the rubber o-rings, seals and washers. The push rod tubes should then be (very) loose. Measure the distance they protrude inside the head to get an idea of what thickness compression plate, if any, you may need. Also, at the same time it is a good idea to put some blobs of plasticine on the piston edges to see what clearance you have to the head. If the cams are fitted and you can turn the engine you could also check piston to valve (pocket) clearance with plasticine.

The o-rings at the bottom of the push rod tubes compress quite a bit, so the gap between push rod tube bottoms and top of crankcase when fitted will only be about 1 to 2mm.

As others have pointed out, the compression plate (at least for the 53 models) were for the compy motors. They have a different bolt spacing so you will have to do some filing work. Compression plate for the 53 C and CS models is part no. 015435. 1/8” thickness. I believe Russell Motors have them in stock.

Good luck
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adz25
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Re: Pushrod tubes

Post by adz25 »

Some fantastic information here thank you!!

This has given me many more options, I have posted a wanted so will see what comes up. I will get some of the Orings as i like the idea of these, and if i go with the decompression plate it will allow me to space it correctly.

The protrusion of the piston is around 1/8th inch so will contact russell motors tomorrow

Thanm you all again!
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Re: Pushrod tubes

Post by Expat »

Have to agree with SPRIDDLER as I followed his suggestion re the ‘O'rings a while back. No leaky since
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