I have been building my A10 too long with several rebuilds. The latest issue is it will rotate taking the pistons from top of the barrel to the bottom, then a solid metallic clonk stops it. The rocker gear, head and barrel are now off, the primary side dismantled and the timing side outer case is off. (The last job was to rebuild the gearbox which I took out from the side). I cannot think how I could have dropped anything down into the engine. I have prodded a feeler gauge either side of the crank via the lower scavenge pipe cover and can feel no loose washer or anything in the way.
Am I missing something or have I dropped something in the engine and have got to remove it AGAIN and shake it upside down.
Thanks
p.s. It says I am a newbie but my account got deleted
If it was mine and a good shaking didn't dislodge anything then i'd be considering taking the engine apart again.
It is a PITA but better than using force and really doing some damage. What happens when you rotate the engine in the opposite direction?
P.S. I've got a 1960 A10. Give the lads a shout over on the A10/A7 forum https://www.a7a10.net/forum/index.php
With the barrels off and primary chain off and timing cover off does the crank still come to a hard stop? I had a very similar problem, its possible you have the same. I had fitted new big end bolts and nuts and the new nuts were very slightly longer. It seem some suppliers list the B25 nuts as OK for the A10 (correct me if its a different bike). If you take the rods in your hand you can spin the crank fine but when they are at the exact angle of the piston/bore the nut hits the case. I had to strip it all down again and get the exact bolts and nuts, not a simple task because too many are wrong and the photos are not clear. I think I ordered from SRM because they do make sure their parts fit.
Hi,
Ditto the bolts and nuts. Many years ago I think I used Triumph bolt and nuts.
Not knowing any better in those days, I stripped it down and filed the nuts at an angle until they did not catch. It is not much but worth fitting the correct ones.
Dave.
Thanks for the replies
Yes it happens in both directions and with all the primary side, head and barrel off. Thanks for the idea limeyrob & Dave Brady, but SRM ground the crank and fitted the con rods a while ago and it turned fine after that.
What I cant understand is that you would not get much more than a washer down there and I've seen them drop through. Would that cause a solid metallic clonk?
I'll find out when I strip it.
When I bought my decrepit A7 I had the same problem. It wasn't obvious what it was until the timing cover was removed to reveal that someone had removed the dynamo sprocket but left the chain in place. This had bunched up around the drive sprocket, and gave a limited movement in each direction and causing a noticeable clonk when it stopped.
Worth removing the oil pump and timing pinions first , to remove any reason externally for non rotating
Try removing the sump plate. You may be able to see what the problem is.
Hi,
A washer could cause this as there is not a lot of room. If you have an air line try blasting through with the sump plate off. Do it on both directions and see if anything comes out.
It is also worth checking the cam shaft. Again not much clearance and the smallest object can jam it up.
Something could be sitting in the oil trough and catching the lobes as they come round.
Dave.
the usual cause of crank stop is a too long primary bolt in the crankcases. have you any of the 3 primary bolts fitted ?
Good point, especially if you have some aftermarket Allen screws.
Hi,
If I remember correctly, the three foremost primary cover ones are bigger diameter and go right through the cases as they also, along with the two hex screws just rear of the engine sprocket, hold the inner primary case on as well.
Even if the correct length, if put in just through the inner primary case they will foul the crank shaft as it rotates.
Dave.
You do have the 1/8" plate and a gasket each side between the inner case and the crank case? Just checking.
I'm embarrassed. I'll tell you what I did so if any newbies do it, or more like me, we can suggest this as a solution.
When rebuilding the primary side, to hold the inner chain case in position I put the three larger screws at the front fully home. It was these stopping the crank turning. Before stripping the engine again I tried a few unlikely solutions.
Thanks for all your help. Anyone got a spare brain?
Sorry Dave Brady I did not mention you got it spot on.
Glad you've sorted it! I'll sleep better tonight ;D
Hi,
Eddie mentioned this as well. We have all had experiences like this and are prepared to share them. The value of this Forum is unquantifiable.
Dave.