A7 compression

[Brandis]

Still having difficulties getting my '47 A7 started.  Really hard to kick over.  What should the compression reading be?

[limeyrob]

Has it just been rebuilt?

[Brandis]

Yes. Recent rebuild.   It's perhaps the last of the first prototype batch, (XAT280), that had a dozen major problems and had total engine failure at !K miles.   SAt in an abandoned warehouse since then.  New Italian made pistons.  Everything else is a mixture of used and old new stock. Total rebuild on the mag.  My compression meter reads 40PSI.   It will start and run if I'm lucky so timings are OK.  New Amal monobloc to replace the old.  My 78 year old leg can't kick it but I'm trying to get it ready to sell.  Might be the oldest BSA vertical twin still around, since 120 of the original stamped 200 never left the factory.  The remaining 80 went to the States.

[limeyrob]

I could not start my rebuilt 350 Matchless.  The engines was OK to turn over but just a bit too stiff to kick at a speed that you create a good spark.
After many attempts and getting worn out I bought a 12v roller starter. I then took the plug out and motored it 5 mins at a time  for about  an hour.  It got much freer  and I was able to start is on the roller.  After about 2 hours total running it span and started fine on the kick starter.
When I rebuilt to Road Rocket I didn't waste time try to kick it until I'd motored it for a decent period on the roller.  Now even with 8.5:1 ist an easy starter.
While the roller / pit starter got me out of a hole it was poorly made and poor value.  If you can borrow a good one that may be the best solution. The problem is that 100 slow kicks will not start an engine with a magneto when 2 hard ones will.

[Swarfcut]

 Another conundrum! Hard to turn over, but in my estimation poor compression so a poor starter.
 
 With plugs out it should spin with little effort. With plugs back in it should almost support your body weight on the kicker. If all is in order mechanically, ignition, timing, tappet clearances etc my guess is that the rings have not sealed and a slug of oil down each bore is worth a try.  A stubborn case like this needs more continued effort than a single kick, and a roller starter or tow start along with a quick spray is a possible solution.*
   Rob's certainly on the money here.


 Swarfy.


 * Ford Escort Van with stuck rings took a couple of miles of towing to eventually come alive after a long sleep back in the '80's. Thank goodness for simple mechanicals! Ran fine for years after that.

[Triton Thrasher]

That’s the lowest compression I’ve ever heard of on an engine that’s supposed to be a runner.

Are you sure you’re getting a proper compression test?

[muskrat]

G'day Jock.
I agree with TT. You need a young fella to give it 10 good hard kicks with the throttle wide open to get a close reading of comp. I don't have figures to hand but it would be fairly low comp at about 6.5:1.
Cheers