Pushrods

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Pushrods

Postby Halfwhelk » Sun Mar 31, 2019 4:04 pm

I have pushrods of different length - the shorter sits below the lip of the rocker box and is difficult to adjust. One is steel (long) and one alloy (short).
I'd like to replace them but they seem to be unobtainable. Is there a source of supply I have overlooked? Can any pushrod in the AMOC spares shop be modified to fit?

I'm prepared to disassemble them and replace the rods. I have a lathe.
Has anyone done this and can offer any advice?
Some research suggests Chromoly tubing is the material to use and I have found a source of 0.375" tube in various wall thicknesses. I don't yet know price and availability in small quantities.

Thanks

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Re: Pushrods

Postby Rob Harknett » Sun Mar 31, 2019 4:31 pm

It may help if you gave the year and model of the bike in question.

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Re: Pushrods

Postby clive » Sun Mar 31, 2019 5:27 pm

I think (but I am bound to be pulled up by El Presidentee) that the steel pushrods were used with with the iron head models and the alloy ones with alloy head models. The club is listing one which appears to be the steel one but again I will probably be corrected!
clive
if it ain't broke don't fix

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Re: Pushrods

Postby Halfwhelk » Sun Mar 31, 2019 6:27 pm

Sorry,
It's a 1955 18CS with alloy barrels.

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Re: Pushrods

Postby Allen_F » Tue Apr 02, 2019 1:30 am

I got my 57 g80 in boxes from a diseased estate and as it turned out it came with the wrong cylinder barrel and piston , there is a lot more to this story but I reassembled it to the point of refitting the head when I discovered that the pushrods were too long, all 4 of them. knowing that I had spares I went ahead and shortened the best two by 1/4" approx., all progressed smoothly and eventually it runs like a clock. The only drawback I can see is that because there is no step in the cylinder barrel to clear the magneto, perhaps it could overheat because of being so close to heat.

Naturally the correct parts would be comforting but having had the cylinder rebored to suit the supplied oversize piston I felt committed.

Shortening the rods went as follows:- After determining the length required put the pushrod snugly in a vice with the adjustment fitting firmly against the jaws, take out the tappet adjusting bolt and through the bolt hole tap the rod off the metal fitting with a drift, the aluminium rod slips through the jaws until the fitting falls to the bench. with a hacksaw hack away, reassemble and Bob is your uncle. It is so easy it will scare you. Pushrod covers are probably wrong but they do the job without mods.

It can be done but because you live where parts abound explore the cost before proceeding.

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Re: Pushrods

Postby Halfwhelk » Tue Apr 02, 2019 10:10 am

Thanks for the advice Clive and Allen.
I went ahead and bought the pushrods (014831) from AMOC parts. Looks like they are the last in the world as they are now marked 'no stock' on the AMOCP site. I seem to be very lucky with parts on this rebuild.
They came coated in tar, which is coming off nicely in a petrol wash. I think they are original factory stock.
They are steel and too long, but I'm not complaining.
I will shorten them. Dick Casey's method on YouTube https://www.youtube.com/watch?v=k6dIdt0EUpk&t=1261s (go to 19:40) looks even easier than yours Allen.

Any advice on cylinder head bolt torque setting? As its an ally barrel they are on long studs through to the crankcase.

Edit - seems Casey's method wont work on steel pushrods as the tube wall is quite thin and there's no internal face to push against. I'll try your method Allen.

Edit 2 - Allen's method won't work either as there's nothing to push against. Pause for tea and head scratching. Then Eureka! A length of steel rod down the inside of the tube pressing against the tappet end, tighten a 5/16" screw against the rod with a bit of heat to help it on its way and the end pops off with a bang (scary amount of torque required). Shorten the rods (1/2") and press the ends back on - hydraulic press required here. Success! Two new pushrods of the correct length.

Cheers
Matt

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Re: Pushrods

Postby 56G80S » Tue Apr 02, 2019 7:14 pm

You'll find there are varying arguments about the torque setting. I used to do these by hand and wind until I couldn't (when 22 years old).

I now realise this is why the ally "pillars" for the head bolts were recessed and one cracked.

Now use a torque wrench, large heavy washers that miss the rocker box (!) and only to 25 ft lbs. I personally think it's more about the equality between the settings and, as per the video, getting there in stages. Give the threads time to work.

As per the video, check the gasket thickness, head to barrel gap and be sure; particularly if annealing and re-using a gasket, that "pinch" is vital.

Works for me.

Johnny B

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