Pushrod Tube Oil Sealing

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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AJSingleDave18
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Pushrod Tube Oil Sealing

Post by AJSingleDave18 »

Hi. I have seen many AMC bikes devoid of any oil leaks so I’m really irritated that I’m having trouble oil sealing my pushrod tubes in the cylinder head. I have had 4 attempts to cure the leaks. Each time the components are carefully cleaned and inspected. No cracks, divots, marks or any reason for the leakage is seen on the head, tube or seals. The anti-extrusion rings are in place and when assembling the tubes are a very tight fit in the seals, making it difficult to fit the tubes even with a smear of sealant to lubricate them. Tightening the cylinder head pushes the tubes down compressing the lower O-Rings. All looks perfect.

Initially there is no leakage, but after about 1000 miles oil starts to smear on the tubes and crankcase and progressively gets worse, until there is a noticeable dribble.

On dis-assembly the tubes are a sloppy fit in the seals and the seals are loose in the head. There is virtually no extrusion of the seals past the anti-extrusion rings. It appears that the rubber seals have shrunk. The seals have come from a range of suppliers.

Is this a common problem and has anyone else found a fix?

I am so frustrated and have given up with the original design so at present I am waiting for some high temperature Viton O-Rings to arrive. I intend to replace each standard cylindrical rubber seal with 2 O-Rings per tube with a spacer between them. These O-Rings are sized be a tight fit on both the tube and inside the cylinder head so the seal distortions will transmit, via the spacer, to a vertical force to compress the lower pushrod tube seal.
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Re: Pushrod Tube Oil Sealing

Post by SPRIDDLER »

AJSingleDave18 wrote: Tue Aug 31, 2021 2:42 pm I am so frustrated and have given up with the original design so at present I am waiting for some high temperature Viton O-Rings to arrive. I intend to replace each standard cylindrical rubber seal with 2 O-Rings per tube with a spacer between them. These O-Rings are sized be a tight fit on both the tube and inside the cylinder head so the seal distortions will transmit, via the spacer, to a vertical force to compress the lower pushrod tube seal.
I changed to 'O' rings about 15 years ago on my '54 G3LS(retaining the other steel washers) even though I had a bundle of NOS 'rubber' sleeve pt. no. 010672 . I fitted BS 210 Nitrile ones and have not had so much as a weep in about 25,000 miles. I think think quite a few of us have adopted the 'O' ring mod.
100_1420 (640x480).jpg
100_1411 (640x480) (2).jpg
Obviously still using the base 'O' ring. You must be able to move the pushrod tube a tad clear of the c/case or the tube will split.
100_1412.jpg
Pushrod tube should move a tad (640x480).jpg
BS210 Nitrile.JPG
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Last edited by SPRIDDLER on Tue Aug 31, 2021 5:14 pm, edited 5 times in total.
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ajscomboman
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Re: Pushrod Tube Oil Sealing

Post by ajscomboman »

We're out of stock of the rings but our new supplies should be in by the end of the week.
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Duncan
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Re: Pushrod Tube Oil Sealing

Post by Duncan »

I think there is an old technical article from Johnny Allen(?) where he cut out a middle section of the original rubber tube and placed an o-ring in the middle. I have used the above 4 nitrile o-ring approach and it mostly works but on stripping down the engine the o-rings are starting to harden, in the future would probably go for Vitron o-rings for longevity.
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Pharisee
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Re: Pushrod Tube Oil Sealing

Post by Pharisee »

I had trouble with the nitrile rings. Changed to Viton (same size) and have had no problem since.
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clive
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Re: Pushrod Tube Oil Sealing

Post by clive »

AjsDave18 your profike does not say anything about the year of your 350. If it has an iron head some of the years required two of the upper rings above the rubber tube sleeve as well as the one below it. But as Spriddler says there does need to be a little movement or the pushrod tube can split (been there of course)
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ajscomboman
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Re: Pushrod Tube Oil Sealing

Post by ajscomboman »

The rubber O rings from the club are Viton according to our order specification.
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Re: Pushrod Tube Oil Sealing

Post by SPRIDDLER »

Pharisee wrote: Tue Aug 31, 2021 10:31 pm I had trouble with the nitrile rings. Changed to Viton (same size) and have had no problem since.
Although my Nitrile rings have been fine I would use Viton ones next time as they have a higher top temp capability than Nitrile.
I don't know why I chose Nitrile rings but perhaps Viton ones weren't available at the time or I wasn't aware of them, but it was 15 years ago and intended as an experiment, I think on the recommendation of one of our German members.
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AJSingleDave18
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Re: Pushrod Tube Oil Sealing

Post by AJSingleDave18 »

Hi.

Thank you for your quick and useful replies plus pictures.

I'm glad that other people have had the same problems and came to the same solutions.
On my internet seach for O-Rings I quickly realised that Nitrile rubber has a max usable temperture limit of 108degC and Viton 200degC. Bearing in mind pressurised water cooled engines run at about 110degC, so I asume aircooled engines are similar. This means Nitrile seals are at their limit.

Regards.
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