Seating Pushrod Tubes

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Seating Pushrod Tubes

Postby Iron Head » Sun Feb 10, 2019 10:43 pm

Made a revelation out on a ride yesterday that has shown the source of an increasing oil leak I have been experiencing. When I rebuilt the top end I didn’t ‘seat’ the pushrod tubes down properly onto their ‘O’ rings and riding at about 45 mph there was a steady ‘bubbling’ spout from the base of the inlet pushrod tube in particular. Panicking about how to fix it was allayed when I pulled both tubes down, probably about 2.0mm, with pliers and all is now dry as a bone - very satisfying!

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Re: Seating Pushrod Tubes

Postby clive » Sun Feb 10, 2019 11:16 pm

Do you have the special flat washer above the top rubber and the special angled washer below?
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Re: Seating Pushrod Tubes

Postby Iron Head » Sun Feb 10, 2019 11:32 pm

Hi Clive yes I was very meticulous to install all of the washers correctly including finding and digging out and replacing the elusive top washer up in the head but, if I recall correctly, I installed the head with the tubes attached and must have installed them very tight up in the head giving, I believe, this big clearance at the bottom of the tubes now corrected.

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Re: Seating Pushrod Tubes

Postby clive » Mon Feb 11, 2019 12:39 am

2mm of movement seems excessive and I am wondering what will stop them moving up again with vibration. Your profile does not state the year of your bike but some years for the iron heads when a compression plate was used two of the top washers were used on each pushrod tube. Might this be the solution? I also noticed that the 350 and 500 washers had different part numbers at least for some years.
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Re: Seating Pushrod Tubes

Postby SPRIDDLER » Mon Feb 11, 2019 9:17 am

You shouldn't be able to move the tubes up or down at all.

When the cyl head is tightened down it should squash the base 'O' rings leaving about a 1mm to 2mm gap at the bottom.

Pushrod tube to crankcase gap (640x480).jpg


When fitted the pushrod tubes should be held firm and you should only be able to lever

the tubes sideways just a tad

Pushrods should move a tad (640x480).jpg


This is the washer arrangement

Pushrod washers and rubbers.JPG
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Re: Seating Pushrod Tubes

Postby Iron Head » Mon Feb 11, 2019 3:51 pm

Thanks Clive and Spriddler for some great feedback. My ‘48 iron head probably did have a compression plate at one stage and (I think) I just used a standard gasket set with no additional washers at the rebuild. Hopefully I’ve got away with just pulling them down to seat them and there was considerable resistance so hopefully won’t migrate up again but who knows!

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Re: Seating Pushrod Tubes

Postby REW » Mon Feb 11, 2019 7:04 pm

I think the same thing has happened over the last 5 or 6 years to my '51 G3. The leak occurs when the engine cools off - not when running when the pushrod tubes are (presumably) expanded slightly.

As for your solution Iron Head, I thought of the same idea but don't want to make a complete mess of the pushrod covers. How did you avoid doing so AND apply enough force to pull 'em down?
Ron

1951 Matchless G3L, thumping round the Durham Dales

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Re: Seating Pushrod Tubes

Postby Iron Head » Mon Feb 11, 2019 7:36 pm

Truthfully Ron they rotate/slide down reasonably easily plus they are pitted as heck anyway and a gentle touch with pliers, even without the protection of a rag does it. Whatever happens the head ain’t coming off again, the bike is running great and I am having too much fun on it. I was sitting in traffic on Saturday and the old girl was being filmed by a couple in an Italian restaurant both waving enthusiastically - felt very proud of an all original ‘roadworn’ bike that was likely last on the roads in the 60’s!

To keep the tubes down, if need be, I have a cunning plan that will involve cutting tight-fitting ‘O’ rings which I will stretch around the top ‘necked’ end of the tubes and then join them again with super glue thereby wedging the tubes downward.

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Re: Seating Pushrod Tubes

Postby Rob Harknett » Mon Feb 11, 2019 8:02 pm

Ashampoo_Snap_11 February 2019_19h22m28s_001_.jpg

From 51 parts list, which will also state Compression plate was fitted G3LS & LCS. G80 G80S, C & CS.
You may be able to squeeze some sealant under the bottom tube rubber, trim when dry, paint with tire wall black allowing paint to run to aid sealing, trim when dry. Perhaps no one will notice it.
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Re: Seating Pushrod Tubes

Postby 56G80S » Mon Feb 11, 2019 8:45 pm

I thought, and IKBA, that someone had made a temporary fix by getting some twine , painting it with Welseal and winding it around underneath the bottom seal?

So long as you dont pull it too tight and interfere with the cam followers.

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