center main bearings

can still buy NF207W/C3 bearings, can be fairly hard to find, bearing supplier I use sources them from Japan I believe, takes around 14 days delivery for that bearing so I buy them 30 at a time
on my own cranks for my own bikes I use standard clearance bearings which is tighter than the C3 spec and I have never had any issues
both my Jota engines and my race engine are built with standard clearance bearings throughout

hardest bearing I find to source is the NJ303W/C3 gearbox bearing
 
redax5 said:
on my own cranks for my own bikes I use standard clearance bearings which is tighter than the C3 spec and I have never had any issues
both my Jota engines and my race engine are built with standard clearance bearings throughout
Click to expand...

I've read here http://www.ahrinternational.com/bearing_radial_clearance_explained.htm that "normal" clearance (CN) is in between C2 and C3, so the switch from C3 to normal doesn't appear to be a big jump.  However, I'm not a bearing expert.
 
redax5 said:
can still buy NF207W/C3 bearings, can be fairly hard to find, bearing supplier I use sources them from Japan I believe, takes around 14 days delivery for that bearing so I buy them 30 at a time
on my own cranks for my own bikes I use standard clearance bearings which is tighter than the C3 spec and I have never had any issues
both my Jota engines and my race engine are built with standard clearance bearings throughout

hardest bearing I find to source is the NJ303W/C3 gearbox bearing
Click to expand...

Hi Red and all

do your engines run any quieter or smoother with the CN "normal" clearance bearings as opposed to the looser C 3 bearings specified by Laverda?

has bearing technology advanced enough since say 1980 to be able to use current modern manufacture normal clearance bearings vs the looser C 3 bearings from the 70's and early 80's, or are things still about the same?

Paul LeClair

ps

Chris, you already know the answer to your bearing issue, just have Wolfgang send correct crank bearings when he sends the Carrillo rods to Mongoose..... ;)
 
Paul LeClair said:
ps

Chris, you already know the answer to your bearing issue, just have Wolfgang send correct crank bearings when he sends the Carrillo rods to Mongoose..... ;)
Click to expand...

The rods are in my hands now.  Gorgeous instruments of reciprocating engine porn!  I have obtained the outer mains locally.  Wolfgang is still away for another week or so.  I'm itching to send the crank to Mongoose!
 
The centre mains are now the most expensive bearing in the engine by quite a margin, my bearing factor sources them from NTN. I use C3 clearanced bearings and insist on steel cages on all the mains.
Ensure your crank rebuilder hones the Carrillos to the correct size before installing, as supplied the big end journal is a little small, they will fit straight out of the box but there is not an adequate running clearance. If ran tight there is a chance of siezure and spinning the liner out of the rod.

    Keith
 
laverdakeith said:
Ensure your crank rebuilder hones the Carrillos to the correct size before installing, as supplied the big end journal is a little small, they will fit straight out of the box but there is not an adequate running clearance. If ran tight there is a chance of siezure and spinning the liner out of the rod.

    Keith
Click to expand...

Thanks - will do.
 
Paul LeClair said:
Hi Red and all
do your engines run any quieter or smoother with the CN "normal" clearance bearings as opposed to the looser C 3 bearings specified by Laverda?
Click to expand...

beats me Paul, we are talking microns difference here as Simon just pointed out and being in the later stages of life I am just happy that I can hear at all  :D

my Jota engines are both smooth but that is probably because I spend a lot of time balancing the reciprocating mass on each cylinder, doubt the bearing clearance is having an effect there
main point is that they are still running, I think, not started either for sometime now, too damn busy

 
Besides temperature and vibration determining whether a normal or C3 bearing is required, the most common being the method by which the bearing is mounted. If the bearing is a press fit on a shaft, a shrink fit or clamping on the outer race will cause the internal clearance to close up.

As there are manufacturing tolerances in a motor, it's usually a safe bet to use C3 clearance bearings. In a worse case scenario, you have a crankshaft where the area that the bearing presses on is a little bit big, the id of the bearing itself is a little bit small and the area of the crankcase where the bearing fits was bored a little bit small. But yet all are in tolerance. So what happens, the bearing will seize. To play it safe an not have the 1 in 100 bikes where the tolerances are all in the wrong direction and the bearing will seize they just eliminate the problem with C3.

Bruce
 
laverdakeith said:
The centre mains are now the most expensive bearing in the engine by quite a margin, my bearing factor sources them from NTN. I use C3 clearanced bearings and insist on steel cages on all the mains.
Click to expand...


Only main bearing cages I found that have caused trouble were the steel variety... usually the RH ball bearing, occasionally a centre main. ::)  No issues at all with the LH roller though.

Been using polyamide caged bearings in my own cranks for decades without the slightest issue.  The 3C has had RHP with plastic cages since 1990, still "as new" when I swapped the crank for the leggera version 2 years ago.  Used the same bearings for the new crank as well, with normal clearance as I managed to get the run-out to less than 0.01mm. :D

Benefit of polyamide cages is that an extra roller can be squeezed in the bearing, and the rollers are slightly longer.  Crank runs quieter, bearings can stand higher loads.

piet
 
You must log in or register to reply here.
Back
Top