pushrod tube question

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Locked
BakerDave
Posts: 28
Joined: Thu Feb 05, 2015 11:19 pm
Location: NORTHERN TERRITORY AUSTRALIA

pushrod tube question

Post by BakerDave »

G'day all

I have been trying to replace head on my 18s and have a problem with seating over the pushrod tubes. After researching on this forum, I believe I must be missing the compression plate underneath the barrel, when the rubber collar and washers are in place the head sits about 3 or 4 mm proud of the barrel and I have flattened out the bottom of the pushrod tubes trying to tighten it down. When I took everything off the tubes and fit them up into the head, it all sat as it should. My question is am I better off to purchase a compression plate, which I believe would make up that gap, or could I simply add o rings till the required fit. This is a bitsa that I purchased some time ago so no real idea of what parts have been cobbled together. The crank case has 49 stamped on it, the magneto is at the front so later barrel, alloy head.

Look forward to hearing any suggestions

Cheers
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: pushrod tube question

Post by clive »

I have flattened pushrod tubes too. In my case the problem was repro tubes which do not have the top edge rolled over. Too much and it damages the pushrods too little and the tube binds on the upper washer in the head rather than passing through it. Original tubes had a rounded top profile. My solution is to force fit the tubes in the head before fitting ensuring the top of the tube has cleared the washer and checking they are protruding through as i tighten the head down. I do not think you need to fit the compression plate but do check you have not got double washers in the head you only require a single on each side. I do not think that the top rubber seal would exert enough pressure to flatten the lower part of the tubes and it must have been metal to metal binding in those top washers. So fitting o rings is not going to resolve it.
clive
if it ain't broke don't fix
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: pushrod tube question

Post by SPRIDDLER »

Did the head seat down O.K. before you removed it, or is this a basket case being assembled for the first time?
As Clive has said, it's easy to think you have removed the top steel washer ('A' or 'B' below) as it isn't obvious when looking and then try to fit a second one.
Your Profile shows the engine to be a mix of '48 to '52 parts so perhaps this illustration may be of some help......
Pushrod tube washers and seals.JPG
Instead of the top rubber collar (Pt. No. 010672) I use Nitrile 'O' rings Pt. No. BS 210 which don't go hard and leak as do the rubber collars. You must still use the top flat steel washer and also the dished steel washer.
Here's just one supplier (pack of 50 for about £6) :
https://simplybearings.co.uk/shop/advan ... ords=bs210

100_1420 (640x480).jpg
100_1411 (640x480).jpg
When all tightened up there should about a 2 to 3mm gap between the bottom of the pushrod tube and the crankcase allowing the pushrod to be moved just a tad.
You do not have the required permissions to view the files attached to this post.
'There is a tide in the affairs of men
Which taken at the flood............'
BakerDave
Posts: 28
Joined: Thu Feb 05, 2015 11:19 pm
Location: NORTHERN TERRITORY AUSTRALIA

Re: pushrod tube question

Post by BakerDave »

Thanks for the reply gents, I will look to see if the tube is coming past the washer. I will post a few pics to clarify. Cheers
BakerDave
Posts: 28
Joined: Thu Feb 05, 2015 11:19 pm
Location: NORTHERN TERRITORY AUSTRALIA

Re: pushrod tube question

Post by BakerDave »

Hi guys, you were on the money with the extra washer. The 1/8th washer was still in place, I thought it was part of the head. Have now removed it and replaced with the smaller washer, rubber and dished washer and everything has tightened down as it should.

Thanks for the help
Locked