3 speed gearbox mainshaft end float

Well I think we have got the gear change spring sorted with the help of some good quality kit from Rex Caunt. So now to the major frustrating hurdle getting classic 175 motor ready for the last (30th) [my 20th] Pukekohe Fe estival. I have built my "Classic" motor from all new parts including D10 cases {ready for the JS 4 speed CR gears} now discover after 45" testing and several rebuilds that there is -47thou insufficient end float on the mainshaft. Hence the tightening up and clutch pushrod welding itself to the inside of the mainshaft (yes I used std bearings and maybe also reduced radial clearances with tight cases/shafts etc) So......, whats the best way to increase the end float, reduce thickness of RLS5 C3 ? The other 3 racing motors I have rebuilt always had plenty of clearance with standard parts. Any suggestions on how much endfloat is needed on the mainshaft and how and where does one adjust ? Layshaft good has needle roller type mod. Previously I have been using thicker sealed EE8 (1/2") bearings to run 13, 12T for trials, sprockets; so std 3/8" could come further out inside outrigger plate with slimmer sleeve gear spacer.

Hi Big John,
Hope you are well down there?
Your mainshaft needs some float and I go for just a couple of thou. The float must be there and measureable but there must be no binding at all.
Assemble the cases with nothing but the mainshaft so there is no mistaking or confusion from any other source, and reposition the RLS5 in the case to suit the float. You may need to modify the seal housing if the RLS5 sticks out (something I have needed to do with cases).
There is a wild variation of case and shaft tolerances with the bantams so I am not surprised you have met with a few problems.
Stay on and ride well!
Alan

John,

if I've understood correctly, you can gain 0.125" endfloat by fitting a std EE8 brg. in lieu of the 0.5" thick version you mention.

Probably mistunderstood though!

Not quite so Pete. My sealed EE8 mod is .125" wider outside the crankcases with an extra 1/8" outrigger plate instead of the standard plate and the oil seal holder. Not really neceesary if using 14T gb sprocket or bigger. I thought my problem was due to insufficient clearance between bearings for the mainshaft. So either I needed to move the EE8 out or surface grinding and thinning LS5. But Dave has gone to a lot of trouble to make a precise mandrel/shaft to measure mainshaft endfloat; by outside the current standard EE8 with feeler guages. He has measured that I in fact have < 0.054" endfloat, too much ! So it looks like my tightening problem is being caused by insufficient radial clearance in the LS5 (C2 stds used so far) as the bearing is a tight ~ 1.5 thou interference fit in new cases and the new main shaft is 1 thou interference in ID of bearing. Hopefully a C3 will be enough or I will be using old low powered longstroke 125 at Pukekohe and then we have the difficult job of maybe slimming the shaft ??? which Dave thinks is a horrible idea.

Hi John,
Have you tried checking a that the bearing is really square in the cases? It helps on assembly to push the shaft fully up to the suspect bearing and give the oposite shaft end a sharp rapp with a piece of brass to slightly shock the bearing into position. You should find the shaft spins freely after that.
This is something I do on all re-builds and seems to get over the bearing positioning problem.
Good luck with it.
Alan

Yes, indeed both of the two LS5 bearings we have fitted and graunched were fitted very square, upto the circlip (which is parallel and square too) and aligned with the EE8 and the shaft turned very freely. Until it has been run, gets very hot and tight. When cools it frees up but the bearing is rough. The mainshaft is new old stock and checked out straight. Been using same Rock Lite gearoil I have used in all 3 motors for twenty years. So its seems the only explanation left is the lack of radial clearance in untested parts. The only thing we have not measured and compared [now I think about it] is the distance between MS and LS centres, will have to check that when I get home. I have never had any such problems with the previously used and worn stuff ! Have even used C2 bearings in gearboxes with out any problems. If anyone knows of a readily available source of a C3 EE8 I would be pleased to know. Can not source in NZ or Sydney Australia today.

Brief chat with Rex Caunt last night and C3s on the way. He also thinks that 1 thou interference of shaft in ID of bearing is too much, so will get shaft made smaller. OK, so if MS endloat is too much where is the best place to shim, between 24T sleeve gear and inside of EE8 ? or crudely push EE8 in a bit ?

Hi John,
I agree with Rex C, the interference is too great and is likely to swell the bearing inner race (could be the source of the problems?). I go for a slide fit that provides some resistance but doesn't need a hammer to get the shaft in!
As for the EE8 I reposition this bearing to get the end float correct, I have noticed that bearings from various manufactureres can be different in widths so it is a good place to get things corrected.
Hope you manage OK with it all and don't forget to put a picture on the email so I can add it into the web site on the racing in New Zealand page!
Cheers
Alan