wrinkleyp Posted May 19, 2008 Report Share Posted May 19, 2008 I have a 1980 Sherpa 199a which I have just partially restored. i.e. frame, brakes, rebore, new carb, repaint etc etc. (Trying to relive my youth according to the wife- rode a DOT in the 60's and a slimline Bultaco 325 in the early 70's) Up until yesterday it was running sweetly. Then a misfire developed which gradually worsened with backfiring etc. Checked spark seemed fine but changed plug...... no improvement. Bike starts no bother but misfires as soon as I ride it. Checked wiring and cleaned earth connections...... No better. Waiting for a condenser from Dave R so haven't been able to try that yet. Decided to check timing and points. Points had closed down a lot so thought I'd cracked it! .No chance - bad as ever. Checked timing, seems fine. Decided that is was time to change the crankcase oil seal as I was this far in! Removed flywheel and stator plate with no hassle. Began to wonder when I saw oil seal retainer.... surface rust on bolts, but they came out OK NOW FOR THE HORROR STORY. The oil seal was full of dirty gunge including bits of metal!!!! Examination of the main bearing revealed that the ball cage had disintegrated and disappeared - all I have are 9 loose balls. Amazingly the crankshaft has no significant play. The engine starts and ticks over in spite of this. HAS ANYONE ELSE HAD THIS HAPPEN? When I first bought the bike (running) it seemed a bit rattly, and when I stripped the top end I found the top piston ring hammered into its groove and small punch marks on the head, but no piston or barrel scoring. Some blow past marks on the piston. I assumed that some grit or similar had got in via the carb. Now I guess I know the real reason!!! Or could this be the cause of the misfire? (No signs of any leakage past the oil seal). I am terrified at the prospect of splitting the crankcase and gearbox but unless anyone knows a friendly mechanic in the North of England I guess I'll have to try. ANY SUGGESTIONS OR ADVICE VERY MUCH APPRECIATED. WrinkleyP Quote Link to comment Share on other sites More sharing options...
motovintage Posted May 19, 2008 Report Share Posted May 19, 2008 most likely your misfire is from a timing change produced from the crankshaft wobble caused by the faulty main bearing , your lucky no more dammmage was done, Quote Link to comment Share on other sites More sharing options...
swooshdave Posted May 19, 2008 Report Share Posted May 19, 2008 Those engines are so easy to split and work on, don't even fret about it. Just do it. Get it torn apart and see what else is damaged. If it's just the main bearing(s), replace and put back together. Quote Link to comment Share on other sites More sharing options...
peterb Posted May 20, 2008 Report Share Posted May 20, 2008 Hi WrinkleyP, As Dave said, these are an easy peasy bike to work on. I never heard of a main bearing cage collapse before, wonder where it was made! Maybe the previous owner had the motor flooded with water at some stage and did not flush out soon enough which may have set the rot in. If you are hesitant about tackling the motor, try BetaPete (at least I think that's his alias) on the forums here, he lives in Guisborough (up toward Middlesbrough way) or for sure, Al the spanner at Derek Whites in Darlington would be more than capable too. Ta ta, PeterB. Quote Link to comment Share on other sites More sharing options...
paulthistle Posted May 20, 2008 Report Share Posted May 20, 2008 It is not uncommon for the bearing separator to come apart. But while you have it apart be sure to split the crank and check the needle bearing separator on the big end of the rod as well. Quote Link to comment Share on other sites More sharing options...
jse Posted May 20, 2008 Report Share Posted May 20, 2008 When I first bought the bike (running) it seemed a bit rattly, and when I stripped the top end I found the top piston ring hammered into its groove and small punch marks on the head, but no piston or barrel scoring. Some blow past marks on the piston. I assumed that some grit or similar had got in via the carb. If the small "punch marks" (sometimes looks like sandblasting) are around the outside of the top of the piston crown, this, coupled with the ring land collapse, is usually a symptom of detonation and could be the source of the main bearing problem. As I remember, the Bul uses a Dykes type top ring (shaped like an "L") so look at the ring land with the ring off. Inspect the head at the outermost part of the squish band, around the outside (you'll sometimes need a magniyfing glass to make sure) to look for small depressions or small ravines where the aluminum has been lost. If the "punch marks" are in the center of the piston crown, it's probably pre-ignition, which is still nasty but not nearly as destructive as detonation (they have different causal factors). If you find any signs of detonation you also need to be suspicious of both rod bearings. The blowby marks on the piston are undoubtedly the result of the rings being trapped in the lands and unable to expand outwards at the top of the bore and seal the chamber area. Jon Quote Link to comment Share on other sites More sharing options...
wrinkleyp Posted May 20, 2008 Author Report Share Posted May 20, 2008 Thanks very much to everyone - especially the reassuring ones! It's great to know there are so many helpful folks about! I guess I'll just have to be brave and try rebuilding the motor myself. Only thing I cannot do is is split the crank to inspect the big end but I was most probably intending to replace this anyway in view of all the effort involved. (When I played with the conrod during the top end rebuild I could feel no up and down play at all, neither could I rock the conrod from side to side (diagonally?). What I could do however is slide the rod bodily from side to side along the line of the crankpin just by a tiny amount - is this sufficient reason to replace it?) Any suggestions where I can get this done, preferably within 50 miles or so of Penrith, Cumbria? Any other bits that anyone would recommend replacing while the engine is stripped - I will be replacing the crank oil seals? Thanks again! Quote Link to comment Share on other sites More sharing options...
t-shock 250 Posted May 20, 2008 Report Share Posted May 20, 2008 Dave rowlandson, at sapphire m/c's at Staveley. Second to none workshop!, loves older bikes. Quote Link to comment Share on other sites More sharing options...
swooshdave Posted May 20, 2008 Report Share Posted May 20, 2008 Any other bits that anyone would recommend replacing while the engine is stripped - I will be replacing the crank oil seals?Thanks again! Crank oil seals are a given. Don't know if the side play is ok. If it is, slap it back together, and make sure the timing is right. Or you can strip it and rebuild or replace everything. Just a matter of time and money. Quote Link to comment Share on other sites More sharing options...
jse Posted May 22, 2008 Report Share Posted May 22, 2008 (When I played with the conrod during the top end rebuild I could feel no up and down play at all, neither could I rock the conrod from side to side (diagonally?). What I could do however is slide the rod bodily from side to side along the line of the crankpin just by a tiny amount - is this sufficient reason to replace it Sounds like the crank is o.k. The side-to-side movement is necessary for the rod to align correctly and have lubrication. No up/down movement in the rod would indicate lower end is fine, providing it is smooth in rotation. Usually pressing a crank is best left to somebody with experience and tools. If you've ever seen a pro align a crank, it looks like they're beating the thing to death, but it's actually very precise. Jon Quote Link to comment Share on other sites More sharing options...
copemech Posted May 23, 2008 Report Share Posted May 23, 2008 Sounds like the crank is o.k. The side-to-side movement is necessary for the rod to align correctly and have lubrication. No up/down movement in the rod would indicate lower end is fine, providing it is smooth in rotation.Usually pressing a crank is best left to somebody with experience and tools. If you've ever seen a pro align a crank, it looks like they're beating the thing to death, but it's actually very precise. Jon Why do I suddenly get this mental image of Jon with a BIG hammer in his hand? Reminds me of one of them movies! Did you remember your hockey mask? Quote Link to comment Share on other sites More sharing options...
davieboy Posted May 23, 2008 Report Share Posted May 23, 2008 I had a main bearing collapse on my 198 a few years ago.The bike was still running,sounded like a bag of spanners mind.Changed them myself,pretty easy to do. Don't be afraid to try,the gearbox all sits together in one crankcase half while you offer the other half to it when putting them back together. Quote Link to comment Share on other sites More sharing options...
swooshdave Posted May 23, 2008 Report Share Posted May 23, 2008 Heck, the first time I pulled a motor apart I just used this as a Guide. A proper manual is only slightly better. Bultaco Overhaul Article Quote Link to comment Share on other sites More sharing options...
loydee Posted June 5, 2008 Report Share Posted June 5, 2008 Yeah had similar thing on 198 Bultaco -ran fine then let me down at start of 1st event. Went to replace points/stator assembly and took seal out to behold a main bearing minus some of it's outer cage :-( Quote Link to comment Share on other sites More sharing options...
steve Posted June 5, 2008 Report Share Posted June 5, 2008 Heck, the first time I pulled a motor apart I just used this as a Guide. A proper manual is only slightly better.Bultaco Overhaul Article Just what I needed - Thanks for posting the link. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.