Getting brained out with this friends BB34 engine. Bought a few years ago and only recently fitted. It was supposedly rebuilt so he fitted it to replace his B31 engine.First start up, horrible clanging noises. Pull it down and find the cutout in the existing piston was too small for it's valve, plus discover it had about ten thou piston clearance. New piston with right size cutouts and new sleeve to suit. Second start up, horrible clanging? Pull down and notice marks in the piston cutout. We get the cutouts widened and deepened to make sure.Third start up, clanging again!! Pull it down again and find a shiny mark under the exhaust rocker where we assumed it was just touching the top valve spring retainer. We take some metal off the rocker area and to make sure we fitted a 3/8 th valve cap for extra clearance. Start it up and now clanging only at revs but not at idle!I'm exhausted and defeated!

Hi Douglas..What cams are you running in it?...Ian

email (option): ian@wright52.plus.com

By the way, that is an Indian tank which was pretty good quality but the front mounting bracket is wrongly placed to cause the tank to be on an angle. I would suggest any potential buyers give exact measurements before ordering.The company apologized and sent him a complete unchromed one for free except for postage.That's service! I think they maybe mixing up M type bracket position as against B type position? All their tanks have lots of internal surface rust but that is of no circumstance considering how easy to neutralize. Put petrol in it!

Tried that too Ian ,there's a pair of M20 cams in it at the moment Closed the tappet clearance to almost nil the same.Did BB34 valves and retainers have the standard width B31 valves and retainers? I wonder if they used the later DB narrower valve diameters?

Hi Douglas...BB valve springs etc. aren't the same as the DB and DBD ones..From you posting it seems you have solved the rocker arm clearance problem....
This may have been caused by a recessed valve seat or a pattern/incorrect valve which is a little too long...
Either of these conditions will reduce pre load on the valve spring and cause it (and the spring and collar) to 'sit' higher in the head, at the same time altering the rocker arm angle and allowing the collar and arm to contact each other......
As the parts in this engine are of unknown origin check carefully that the valve springs are not becoming 'coil bound' or too close to it at maximum lift..Also that there is clearance between the under side of the valve spring collars and the top of the valve guide shoulders in the same position...

Moving away from the head...If the crankshaft is not running within the specified concentricity limits it will make the engine very noisy, more so with alloy units that don't 'damp out' the sound so well as the iron ones...This is because as the mainshaft turns through an eccentric rotation the clearance between the crank pinion and the cam pinions becomes excessive...
As the cam lifts the follower it is pressurising the valve spring and the whole assembly is under compression, taking up any backlash...However, just as the exhaust cam moves past the point of maximum lift the valve spring then starts to 'drive' the valve and cam, the camshaft action is no longer the 'prime mover'...
At this point any slackness between the gear will be instantaneously 'taken up' and this causes a sharp mechanical noise and makes the engine very rattly...
If you turn the engine over very slowly with a spanner on the crank nut you can see the cam teeth jump forward and hear the 'cick' which is amplified by engine speed....
This effect is always more noticeable on the exhaust cam... Ian

email (option): ian@wright52.plus.com

Douglas,

An alloy BB34 engine is a valuable lump that could be wiped out by a crank failure. With all the shortcuts and bodges you found in that presumably rebuilt engine I'd not trust it to ride around the block without a complete teardown and inspection.

Ian is correct. I'd pull the crank, check it between centers, clean the sludge trap in the crankpin, take a good look at the main bearings and the oil pump. Check the rockers for excessive clearance on the shafts, look at the valve seats and clean them up.

Jeff

email (option): jjbandoo@aol.com

Douglas,

An alloy BB34 engine is a valuable lump that could be wiped out by a crank failure. With all the shortcuts and bodges you found in that presumably rebuilt engine I'd not trust it to ride around the block without a complete teardown and inspection.

Ian is correct. I'd pull the crank, check it between centers, clean the sludge trap in the crankpin, take a good look at the main bearings and the oil pump. Check the rockers for excessive clearance on the shafts, look at the valve seats and clean them up.

Jeff

email (option): jjbandoo@aol.com

Nice bike !! Is the frame a B31 and fits the gider fork ?. Theo Schipper

email (option): oldbikes@kpnmail.nl

I forgot to mention it's had new seats and exhaust valve. No one told us by the way the original seat is threaded into the head. It had our engineer confused!There is no bigend up and down movement. I don't really expect an immediate solution, I was really just venting.I will walk away for a week and try and think what else i can try. Yes it's a rigid B31 frame with M20 girders. Handles beautifully. Tempted to put the original motor back in!

The girders fit the frame with no modification Theo. Go for it!