Continuning on from my primary gear removal thread: http://ducatiforum.co.uk/f41/desmoquattro-crank-primary-drive-gear-removal-17633/ I've now split the cases and stripped the conrods off the crank. What was underneith wasn't pretty. The conrod that had siezed had rotated one shell around and underneith the orther so they were overlapping. You can see the 10mm or so overlap in the photo below, and the "gap" left on the otherside of the crank pin. The shells of the other bearing were relativley unscathed other than the overheating. I haven't removed the crankshaft plugs yet to see what lurks inside, presumably it was an oilway blockage that lead to the bearing failure. On inspection of the Crank Pin I was quite hopeful to begin with as the side where the bearings had overlapped was pretty smooth and in good condition. The otherside however is quite galled. My original plan (pending condition of internals on strip down) was to renew and refresh and upgrade the motor with some DP 853 pistons I have. I'm still unsure if I should go ahead with the rebuild or just scrap the motor, puttign anything reuseable on here and eBay. So the question is, is it possible to get the crank reground? And is it possible to get oversize big end shells to go with a reground crank? Or does anyone have a 748 crank they don't need that can go to a good home for a new life?!
Not a pretty sight Widget The scoring looks quite deep from what I can make out in the photos. I don't know what oversize shells are available , give Moto Rapido a call they should know.
I've just had a chat with Dave Robinson about it. My house is quite close so I slung the crank in a rucksack and took a walk round. Surprisingly he said it wasn't that bad, and that he had seen worse. The scoring looks very bad, but when you rub you finger across it it isn't as bad as it looks. Also what looks like bad pitting I think is dirt etc. DR suggested calling Baines and asking them about regrinding. Apparently it can be done, and bearings are availible.
So just had a chat with Geoff. Cranks can be reground, and he has oversize shells in stock. He recons it will be around £400 for a regrind and a set of shells. However he says that the two companies he has used for regrinds, he can't really vouch for their work. Not because it isn't good but because he thinks its very much luck of the draw. He says he's had very good regrinds that only last 500 miles, and others that are still going strong. I also discussed my potential 853 project with him, at which point he tried to sell me a 916.......... So I'm not sure what to do. I don't "need" to rebuild this engine as my 748 has a replacement engine in it that is running as sweet as a nut. The intention was to rebuild it as the 853. I'm now getting cold feet and thinking about what the money from selling the DP 853 pistons, and other engine parts, could do for my next project..... Decisions, decisions.......
Problem is it don't just stop at bearings and a regrind, there is the oil pump to consider and of course where all the bits got to, not forgetting why it went in the first place. As for the price of £400 i think that is reasonable as i recently found out that the oversize bearings are a lot more money than the std ones, possibly around £35 per half. changing the pistons is always a good idea because if you look at them closely you may see steel that gets embeded in the skirt, i have seen this happen and it is not nice.
The crank has obviously heated up quite considerably so the crystalline structure of the metal will have changed but nobody knows by how much, whether it was entirely local to the crankpin or extended into the junction between the crankpin and the crankwheel, always the place that cranks break. Regrinding will reduce the size of the crank pin and reduced its strength as well and then you want to put oversize pistons on it. I think you are asking for trouble.
It might be cheaper to try and get a 748 crank possibly an R off ebay, likely to cost less in the long run even if you change the big ends and the the rod bolts are good.
Yep I think thats the route I would take if I was going to rebuild it. I've pretty much decided not to though. Keep an eye on the for sale section! If anyone is interested in a set of DP 853 pistons then please send me a PM.
As has been said by steve R these engines all use the same crankpin size, you can get undersized shells for these but as i said they are more cash, they are available through ducati. there is another route: I think the same size crankpin is used on a fiat engine, i used some shells a while back but the tang on the bearing is in the wrong place so has to be ground off, this has no effect or detriment to the motor, i will try to find out what engine they came from unless anyone else knows. The strength of the crank is not a problem here as all of them are the same size even up to the 1200's so a 748 is no sweat provided the radius is ground correctly and it is crack tested. Getting hold of a 748 crank is not as easy as it sounds, if you see my earlier posts i am after the same thing and two i have looked at from ebay have been worse that the one i have got, you also have the added bonus of finding the correct crank for the alternator as there are two different ends/ splines. I am just looking into trying a 600/620 crank as these may be the same, anyone looked at this? Good luck!
They are just the poverty spec pistons I'm afraid. Photos here..... http://ducatiforum.co.uk/f20/ducati-performance-853-pistons-748-crank-cases-17742/
On the subject of Italian half-shells, here's a prettier one to cheer you up - Botticelli's Venus on the Half-Shell:
Ha ha ha!!! Brilliant. Yep poverty spec is frequently used on another forum - basically anything bog standard spec is poverty. See also chav spec and peado spec.
