Main bearing clearance

[TotalNZ]

Crank Main bearings C3 or C4?

[TMKIWI]

I use C3.

[TMKIWI]

Just checked my TM parts manual and it lists C4 for crank and C3 for gearbox.

[TotalNZ]

Yeah my TM manual lists C4 also but the mains it came with are C3 and i believe most of the aftermarket main kits i've used ie allballs and most of the koyo and nsk kits are all C3.

[vetman]

what year bud
mine says c4 as well cant say ive split the cases yet but its on the cards

[TotalNZ]

what year bud
mine says c4 as well cant say ive split the cases yet but its on the cards

My TM's an 09 but i've got some microblue bearings coming for it. It's my CR that needs mains.
The TM and CR and KX's and RM's and probably just about every other 2T 250 all have 63/28 mains. Now I've used aftermarket kits before and pretty sure they've all been C3. Now looking through my TM manual and doing a little research am thinking C4 is required.
All the TM manuals spec C4 but interestingly mine came stock with C3, go figure.
Just hoping for some input from guys in the know.

[TotalNZ]

what year bud
mine says c4 as well cant say ive split the cases yet but its on the cards

Hey Vetman you should check my other piston post, might be relevant to your TM. although i hope not for your sake.

[vetman]

yeah saw them, ouch im getting up to 60 hrs now on my piston ,had two rings in the mean time so not so bad but will overhaul before something bad happens ,looks like the new conrods from tm are quite well priced so ill do that and look at a double ringed wossner  ,got to figure out what size yet I think my barrel has got a c stamp but last time I pulled it down the piston had size markings for a a stamp so a barrel measure might be required I think.

[TotalNZ]

yeah saw them, ouch im getting up to 60 hrs now on my piston ,had two rings in the mean time so not so bad but will overhaul before something bad happens ,looks like the new conrods from tm are quite well priced so ill do that and look at a double ringed wossner  ,got to figure out what size yet I think my barrel has got a c stamp but last time I pulled it down the piston had size markings for a a stamp so a barrel measure might be required I think.

I wouldn't worry too much they'll do 60 hours easy with a couple of ring changes, that piston looks that way because of another problem. I'll post up pics on the other post. I wouldn't bother with the twin ring piston i just use the wossner single ring. Mine doesn't have different sizing options, there's just one size available and it's been sweet as.
TM use a proX rod as standard so shop around and you may find one cheaper still. It's the same rod as the case reed CR's so fairly common.

[scotty dog]

Excuse my stupidity but whats the difference between C3 & C4? And what does it mean?

[TotalNZ]

Excuse my stupidity but whats the difference between C3 & C4? And what does it mean?

C3 or C4 refers to the internal clearance in the bearing. A C4 bearing is usually specced for higher heat applications as it has a slightly bigger clearance.

[scotty dog]

aha thanks, ya learn something new every day

[Uniflow]

It also depends on the fit, 0.03 interference  I would use C4,   0.01 to 0.02 you could use C3. I use C3 in all my engines and gearboxes. More than 0.035 ( mm ) is too tight and you will have bearing problems. I've just had to tweak an engine case out to 0.02 press as it was 0.04 press and kept having bearing problems ( main bearing ). I'm talking outside fit to case. You need to be able to feel clearance ( wobble the inner bearing housing a little bit ) on the bearing after it has been fitted to the case. C4 clearance is often used as a "fix" if cranks are not properly alined after manufacturing. Example, Rotax aviation engine ( twostroke ) has C4 bearings as they are only pressed to within 0.05 run out at the factory, poor manufacturing job in my opinion. You should be looking at less than 0.02 run out ( out of true alinement )max.