Engine won't turn

Persa · Post by **Persa** » Mon Aug 04, 2008 9:01 am

Hi

After doing a second rebuild on my 1963 G12 CSR including regrinding the crank and new conrod bearings, something exceptionally weird happened yesterday. After doing a couple of warm runnings followed by torquing, the third time I was about to start the bike the kick lever was stuck. After investigation and removal of transmission chain it's now clear that it's the bloody engine that won't move. I can't belive it! Pistons are in (almost) bottom position. In a moment I'll go out to the bike with a friend to see if we can figure out why. Scary though, since the only reason seem to be a piston that "nipped" or possibly some shit in the the timing wheels or so, not likely though. I've tried to put a high gear in and push n' pull the bike back and forth without result. Any suggestions?

Regards

TommoT · Post by **TommoT** » Mon Aug 04, 2008 10:45 am

quote:
Hi

After doing a second rebuild on my 1963 G12 CSR including regrinding the crank and new conrod bearings, something exceptionally weird happened yesterday. After doing a couple of warm runnings followed by torquing, the third time I was about to start the bike the kick lever was stuck. After investigation and removal of transmission chain it's now clear that it's the bloody engine that won't move. I can't belive it! Pistons are in (almost) bottom position. In a moment I'll go out to the bike with a friend to see if we can figure out why. Scary though, since the only reason seem to be a piston that "nipped" or possibly some shit in the the timing wheels or so, not likely though. I've tried to put a high gear in and push n' pull the bike back and forth without result. Any suggestions?

Regards

Per,
just a few thoughts to maybe calm you down a bit. It's a good thing the engine didn't seize up while running. So damage is hopefully not too severe. If one of the pistons has seized, maybe a honing the bore will do the trick. Also you may want to check the the piston to cylinder clearance, either by asking the machinist or by measuring. There have been stories told here about cylinders being bored out to too small clearances. If a seizure is not the problem all sorts of things could have happened, blocking the drive train somewhere. Let's hear how it goes, you have my sympathy on this one, it's b****y awful having a freshly rebuilt engine lock up like that (been there, done that...)

Persa · Post by **Persa** » Mon Aug 04, 2008 4:18 pm

Thanks for your tips Tommo! Now the engine has been stripped of heads, cylinders and taken out of the frame. Hear this. One cursed conrod bearing had stuck in the crank, I'm having a hard time beliving it. So now I can only wait and see what conclusion my friend comes to when finding the reason for this. Second time this happens now and I'm seriously starting to belive what my mom's old uncle told me. "Per, I think Belsebub jumped into your machine".

RegardsEdited by - Persa on 04 Aug 2008 3:19:34 PM

g80csp11 · Post by **g80csp11** » Mon Aug 04, 2008 7:38 pm

Assuming it's a AMC twin and the problem happened when you rebuild the bottom end , you should check the bearing shells. if you fitted mini shells they are actually wider than the AMC original a,d need to be reduced to fit correctly . if you don't do this the bearing shell will pick up on the radius on the crank .

Persa · Post by **Persa** » Mon Aug 04, 2008 10:14 pm

Oh! So, what you're saying is that the conrod bearing shells ordered from the Club (JSL) doesn't fit right on to the crank? Sounds very strange to me. If so, how can I know how much they need to be "adjusted" and how should it be done?

g80csp11 · Post by **g80csp11** » Mon Aug 04, 2008 10:56 pm

It should not be a problem with correctly supplied parts , the best way is to compare the width with the old ones . of course the problem could be the radius on the reground crank. Usually if this iis the problem the con-rod is tight to turn when torqued up .
Before you strip out the engine remove the barrel / head and piston.
The rod should fall under it's own weight and be evn in all positions . you shoudl not have to apply force .
In the past when I've had mini-shells i reduced the width with wet / dry paper , making sure to clean well afterwards

Groily · Post by **Groily** » Mon Aug 04, 2008 10:59 pm

Reckon anything from JSL should be fine as they're the right bits.
Thing is that BMC A Series Mini shells are a close fit and many bikes have run them in the past. There' some good tekkie stuff on the site somewhere explaining the ins and outs of these substitute parts and in what respects they fit, in what respects they don't, and what the tolerances are.
A big end seizure at zero miles is a function of a regrind that didn't get done to size, an oil starvation problem for one of many possible reasons, or a problem with the con rod and end cap. Hopefully nothing to do with the quality of the assembly. If the rod's eye had got out of round, and the rod had been inexpertly restored to shape (which happens), or not restored at all . . . its worth getting the rods very carefully looked at if the other causes can be eliminated. But I would suspect an oil problem. It's very frustrating and I hope the reasons can be ascertained so you know it won't happen again.

TommoT · Post by **TommoT** » Tue Aug 05, 2008 12:17 am

Also worth checking is if the shells have the "toungues" that keep them from turning in the rod, in the right place. I seem to remember that an incorrect mix of shells and rods from different years could cause problems in this area. But as already mentioned lack of correct radii of the journals spring to mind. I don't suppose JSL have supplied BMC Mini shells without making a note of that!? No, surely not. Best of luck Per and keep us posted.