vibes and running in.

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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vibes and running in.

Postby Stephen G80 » Sat Aug 12, 2017 3:26 pm

I did not rebuild by G80 '54 but the previous owner had re a new piston, re-bore etc at the very least. I am noticing as I put the miles on and increase the maximum revs on each run and more cruising at 55- 60mph she seems to be losing a lot of the vibration lower down. Is this shift in the rev point at which vibes kick in normal as the engine settles down and is run in?

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Re: vibes and running in.

Postby Rob Harknett » Sat Aug 12, 2017 5:33 pm

http://archives.jampot.dk/book/Owners_m ... ingles.pdf
Correct running in is important, in particular to the bore. The tighter the bore the longer the running in period. I have run in many new cars, no two being the same. One such car proved to have a very tight engine. Easy to discover with a car by switching off the ignition. If the engine stops dead, the engine is still very tight. I ran one car in for over 10,000 miles before I considered the engine run in. Refer to your bikes manual for " running in " procedure. Changing gears often to avoid overloading the engine is also good practise. When run in, the engine should run more sweetly with less vibes at cruising speed. Running at 60 MPH with a wide throttle opening is not advised. Read the book if you have not got it see the above link.

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Re: vibes and running in.

Postby SPRIDDLER » Sat Aug 12, 2017 5:52 pm

I only have experience of Heavyweight singles. My (fully run-in) '54 G3LS is exactly like yours, Stephen. It has a sweet spot apparent at 55 to 60 (and a bit more) at which point th'engine becomes (relatively) smooth and quiet and she seems to surge forward and run like a turbine. I have often cruised for perhaps an hour at a time mostly in this range on long trips abroad. (Strangely most of the tedious noise comes from carb slide and rocker box chatter which I dampen with a rag stuffed in the gap between the rear of the tank and the front of the dualseat. Works a treat ;) ).
The engine speed at which piston/conrod/flywheels balance best is a compromise (it cannot be at all revs) and usually designed to be at its best at around 'normal' cruising speeds. A heavier or lighter piston can shift this smoothest rev range a couple of hundred rpm up or down the scale but yours sounds about right.

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Re: vibes and running in.

Postby Stephen G80 » Sat Aug 12, 2017 10:45 pm

Thanks for those insights gents. Useful as ever :-)

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Re: vibes and running in.

Postby Chris Berry » Mon Aug 14, 2017 10:12 am

I have been running in my G80 engine and have just started opening her up a bit after 1000 miles. I am lucky in my area as there are some mild to medium hills where I can apply a little pressure on the rings without over loading the engine. For the last 200 miles I have been cruising around 40 - 45 MPH which the bike handled well. On my last run I cranked her up to 55 - 60 and she purred like a kitten. Which suggests the 'sweet spot' mentioned is well founded. I'm still not ready to push the old girl up some of the steeper hills here (we call them mountains) but that will come. For those who have read my previous posts (two seized valves and a shattered barrel). I am starting to enjoy the ride. Stephen G80 I'm sure you will also.

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Re: vibes and running in.

Postby Stephen G80 » Mon Aug 14, 2017 5:23 pm

thats interesting Chris - sounds like you have earned you kitty after all those seizures! Best wishes.

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