350 Conrods

[TonyH]

Hello,

does anyone know if you can retro fit the better conrods from a plain bearing crank onto the early double roller bearing type crankshaft?

Thanks for your help, Tony

[EVguru]

I haven't noticed any difference between the rods and there's no reason why there should be. There was apparently a spate of rod failures VERY early in production, but I think that was traced to faulty bolts and they changed to stud and nut as part of the cure.

[spub]

If you add plain bearing conrods to an engine designed for roller bearings, you should also consider a new pump, since plain bearings generally require higher oil pressures to maintain the oil film, which acts as the bearing surface, in place. II think roller bearings got a bad rep from the bevel Ducatis, which used roller bottom end bearings and experienced premature bottom end wear in the 70s and early 80s. They changed to plain bearings on the late Mike Hailwoods, and the problem was much less, but this was a resdesigned engine (as opposed to simply swapping conrods). Laverdas use rollers, and those bottom ends are bomb proof, and ditto with many Japanese bikes that use rollers, so I don't think rollers themselves are bad, the system just has to be properly designed.

[EVguru]

Early V-twin Morinis (pre-1976 or so) used a ball race on both sides of the crank. The one on the timing side was meant to be a slip fit (for expansion) on a hardened sleeve pressed onto the crank. It proved difficult to hold all the tollerances required and the timing side was later converted to a plain bearing. The big ends were always plain bearing.

The oil pumps are the same and I don't think the pump drive was changed although I'm not 100% certain. Since the usual modification is from plain bearing to a roller that requires less oil there is no issue.

[Steve Brown]

While we're talking about roller main cranks, (hijacking the thread) can anyone tell me (eg Paul) what spec of roller bearing to replace my timing side ball main bearing with, please? I can find equivalent size roller bearings on the simply bearings site, but would like to be sure I'm not missing some vital point before I go ahead and order.
Thanks in anticipation,

Steve

[TonyH]

Firstly thank you for replys about conrods, but while we are now all talking crankshafts here is another query for people to ponder (sorry i've hijacked this post back!). I'm planning to build my ultimate 350 and have both an early crankshaft and a later type (from a X2) - does anyone have any thoughts on whether i am better using the early crankshaft with later rods and upgraded roller bearings or the later crank and conrods but converted to roller bearings (is that cost effective options? sounds expensive!). And if i alter the later crank will it fit into my older 'S' stamped crankcases?
i think one day i should stop spending my day dreaming of my morini and get on with some work!!!
Thanks everyone, Tony

[EVguru]

While we're talking about roller main cranks, (hijacking the thread) can anyone tell me (eg Paul) what spec of roller bearing to replace my timing side ball main bearing with, please? I can find equivalent size roller bearings on the simply bearings site, but would like to be sure I'm not missing some vital point before I go ahead and order.
Thanks in anticipation,

Steve

Just go back through some of the old posts like;

viewtopic.php?f=4&t=324
or
viewtopic.php?f=7&t=208

[Steve Brown]

Just go back through some of the old posts like;

viewtopic.php?f=4&t=324
or
viewtopic.php?f=7&t=208[/quote]

Thanks Paul, knew you'd come up trumps! Soon have a lessy noisy engine then

Steve.

[SupermotoDave]

I am sure that there were 2 changes to conrods in the early years, both the stud size (dia) and the change between bolt and stud but this late at night I cannot remember any more, but later rods were always a retrofit option and many were done. The rods have always been plain bearings so that will make no difference, but when the engine was improved to the plain main bearing, although the pump was not changed, the oil pump drive on the crank was changed from a 6 start to a 7 start thread. A quick bit of arithmetic shows that this increases the oil flow by 1/6th to feed the plain bearing.