AJS & Matchless Owners Club

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?

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.

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.

Thanks for those insights gents. Useful as ever

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.

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

Resurrecting this thread as it is relevant and I'd search for others experiences. I've now covered about 40 miles since start up after fitting the relined barrel and standard (JP) piston. Clearly I'm an animal and after the first 10 miles at 30mph, 5 miles at 45 mph and 20 miles at 45mph, this was my experience.

That first 10 miles were a bit worrying (two short stints) as everything seemed noisy, more so than with previous rebores, and the spark plug was very sooty. another short stint was better. Then 20 miles at a steady 45mph pretty flat road and a plug chop showed the plug a nice colour (mid brown centre insulation and everything else clean) running smoother and less noisy.

Made me wonder if I would've made it to the Jampot after all.......................................

Anyway, p[lan to stick at the 40 - 45mph for a while but wil take the throttle a bit wider in short bursts as don't want to set up any kind of ridge by being over cautious - my worst trait.

Ha Ha.

I'll wait until I hit 100 - 150 miles before slowly upping the ante but there's no hint of any distress now. Need to hit 500 miles before tightening the head down; I know some others don't and I don't go in for the wind it until it won't approach anymore but that's off topic.

Need to sort out the severe exhaust camwheel end float, another off topic so don't respond.

Hope to show up at Alternative.

Johnny B

Now hit 100 miles and on very slight downhill also hit a short burst at 65mph (indicated) and Matchless just seemed to want to keep increasing speed. I'll be keeping to the 40-45 most of the time ethough for another 100 miles.

Sheets of mixed thickness shim arrived today so may be dropping timing chest cover off and fixing exhaust camwheel end float; not keen on moving the bush. Now where are those hollow punch thingies?

It's a nuisance having to re-time the ignition because it seems just nicely set.

Johnny B

56G80S wrote:Now hit 100 miles and on very slight downhill also hit a short burst at 65mph (indicated) and Matchless just seemed to want to keep increasing speed. I'll be keeping to the 40-45 most of the time ethough for another 100 miles.

Sheets of mixed thickness shim arrived today so may be dropping timing chest cover off and fixing exhaust camwheel end float; not keen on moving the bush. Now where are those hollow punch thingies?

It's a nuisance having to re-time the ignition because it seems just nicely set.

Johnny B

How much end float do you have and is it detrimental to the bike's performance?

Haven't measured it yet, could be as much as 1mm. I was in a rush to get the whole back together at the time.

What I've done before is to put a ring of soft electrical solder round the outer stub and refix the timing chest cover fully and take it off and use a vernier gauge to measure the play.

Daft thing is I can't recall whether I put the shim inboard (conrod side) or outboard (magneto side) of the camwheel!

Performance is fine but I realise there needs to be some endfloat, I've previously not allowed more than a few thou.

Johnny B