YPVS crank into LC cases

[higgsy]

Sorry guys I know this has been covered before but I can't find the thread, I seem to remember it's fairly easy but do I have to make the crank a different width or is it a case of a little machining to the cases?

Cheers

Higgs

[LC_BOTT]

I'm no expert, but think the YPVS crank is a little wider, 2mm+ but have heard some do actually fit (not 100% on this though) without machining, so worth a try just to see, otherwise it's going to be a bit pricey unless you can do it yourself???

[higgsy]

Yes I believe it is 2mm, machining the cases isn't a problem, but I seem to remember somebody saying it fits into the later cases without machining? Just trying to save myself work Lol

[bare]

All 3 of MY 4y3 LC cases accept my '87 IUA crank.. period.
Yes It's tighter than the LC crank fit.. but it fits 'fine'.. reliably.
Only issue is that the valvie cranks' outer bearings' circlip groove is offset ~1+ mm .
Apparently there was large interchangeability/parts overlap at the switchover from LC to valvie engines.
Reputedly some LC's left the factory floor with Valvie cranks and even a few Valvies with LC cranks.
Having said that, Any LC case can be easily /affordably and effectively machined to accept the Valve crank
Only 1 mm needs removal from the inside of the case's outer bearing faces. A Simple procedure.
SCRacing.com requests a $100 fee for this, Should one want it.

I have heard of, but not personally seen, Valve cranks being retrofitted to Aircooler 350 cases, without herculean efforts :-)

[rich]

Hi mate, I think it's a case of it 'might' fit. I reckon it's probably a tolerance thing depending on how the tight the side clearance is on the big ends as that will affect the overall length of the crank. Having said that, even if it did fit then the flywheel side rod would potentially be offset slightly from the centre of the piston although I don't know if that would matter?

[bare]

Welll.. the resultant clearance of the V crank in the 4y3 case is surprisingly good actually, way beyond a simple and Imo monsterous 'Tolerance' issue.
I thought similarinitially, but a moment with my Calipers revealed Exact measurements No tolerance errors at All. Those cases were intended for a Valvie crank.
Rod offset is a non issue, possibly an issue with an LC into a Valvie case, according to Scott Clough (SCR) whom I've known since he was running an RD 350 proddie as a privateer back in '73.
I was running a team (3 :-) of TZ's for the Yamaha distributor.
He kept up racing, still does and still wins... his knowledge is subsequently Massive and Current
I walked away from it all, never looking back, after 3 of my friends/riders Died on our TZ's.

PS: I'd give serious thought as to fitting a Valvie crank. It's Wayy stronger than the LC version and that "extra' mm on the rod Big ends alone is worth the price of admission IMO.

[higgsy]

Yea fair point Rich, one for Uncle Bob I think :-) Bare the bearing offset won't be a problem, sure we can get round that somehow. I want to use the valve crank for the reasons you describe, it's stronger and this motor is going to get some serious abuse :-) The YPVS crank is a lot more suited to race use, especially with the flat cage bearings.

Cheers fellas

[bare]

Sept 29, 2013 18:31:53 GMT 1 rich said:

Hi mate, I think it's a case of it 'might' fit. I reckon it's probably a tolerance thing depending on how the tight the side clearance is on the big ends as that will affect the overall length of the crank. Having said that, even if it did fit then the flywheel side rod would potentially be offset slightly from the centre of the piston although I don't know if that would matter?

Naww.. that doesn't make much sense as the Labyrinth seal MUST be centered.
So Each crank side is 1mm off set. BUT the rod centreline is only 0.5mm offset due to it's 1mm wider Big end bearing :-)
If one considers a 0.5 mm offset as problematic/significant .. then you could be correct.
But I don't think it's even relevant.

[Norbo]

The lc crank is actually a little longer then the ypvs crank the timing web sticks out more and has more threads on it . if you line up the centre web as you have to you can see a difference in the main bearings not lining up but I would think as bare says the difference is not enough to stop them fitting as he clears has tried it and fiends in his cases that they do indeed fit. I would think they are a little tight but if he has fitted them then the do fit . However I think I would be tempted to remove 1mm from ether side to allow a little more room for fuel and oil flow around them.

[t500racer]

I have found that a YPVS crank will not fit with enough clearance in two sets of Canadian LC cases (4Y3). I was getting less than .5mm per side around the crank wheels. Perhaps some will fit, as Bare has found.

I can tell you that the +4mm stroker YPVS/Banshee cranks will NOT fit the 4L0/4Y3 cases without "trenching" for clearance. This is contrary to what a big time two stroke parts dealer in Oz told me as he was pushing to get me to purchase his special +4mm LC crankshaft. The required machining leaves the sealing area very thin at the crankcase halves. If I had it to do all over again I would send the cases to Scott Clough to be machined and fit a standard YPVS/Banshee/ crank.