750 SF1 conrod roller bearing

R

R1220

New member
Location
United Kingdom
Hi everybody.

I tried to look in the previous posts about the roller bearing in the 750sf1 conrods.
On laverdamania there is the full list of bearings except those.
If no specific code is available, are there any tolerances that need to be considered? Or just crankpin and conrod diameter measurements are enough? (!?)

Unfortunately, I do not have any of the aluminum cages, nor a single roller to measure.

Thank you

 
Looking forward to some explanations from those who rebuild these cranks.
I have the notion that the roller cages are unobtainable.

Paul
 
Paul Marx said:
Looking forward to some explanations from those who rebuild these cranks.
I have the notion that the roller cages are unobtainable.

Paul
Click to expand...

Except if you make them yourself, which isn't viable at all (and not at all easy without very specialist machinery). :D  Big end bearing dimensions are quite unique, I haven't found any direct replacement so far.

Most cages can be re-used, but new rollers are a must.  In their endless wisdom, the factory fitted under-size rollers, the wear and tear in the rod big end now allows fitment of standard rollers.  But, it is seldom that easy, both rods and pins are often ripe for replacement.  Replacement crank pins are available, so that's half the problem eliminated.  Rod big ends are often oval, which can be dealt with to a degree with the fitting of oversize crank pins.  If the inner bearing race begins to break up, the rod is scrap.  To my knowledge, nobody has been sucessful with boring out the rod and inserting a new bearing race.  The big end is quite thin, boring this to accept a race will considerably weaken it.  The race itself needs to be of a certain thickness in order to take the loads.  So, sort of a dead-end street...

piet

 
The rolleres are ? 5 x10 ( actually ? 4.985 )
I just reconditioned my crankshaft with Carillo rods , and all new rollers, but luckily
the cages were ok.
The rollers looked good, but Wolfgang advised me to replace them
 
Thank you guys.


BOETJE said:
The rolleres are ? 5 x10 ( actually ? 4.985 )
I just reconditioned my crankshaft with Carillo rods , and all new rollers, but luckily
the cages were ok.
The rollers looked good, but Wolfgang advised me to replace them
Click to expand...
Can I ask how much you paid for the conrods and where you bought them? Mine are shot. there are heavy roller marks in the big end. but luckily the crankpins are perfect.
 
Rob said:
Get in quick - thought the cut off was the end of the year?
But - don't Carillo rods need honing to size?
Click to expand...

yes Carrillo conrods do need honing to size but does not matter anyway as Wolfgang has no 750 SF Carrillo conrods left in stock anymore
and he is not going to place an order for anymore stock
I know this as I bought all of his remaining 750SF Carrillo conrod stock

 
I found when I first opened my SF1 crank that the cages had worn into the big end race in the rod, but where the rollers ran looked in excellent nick - I never measured them though, so quite possibly ovalised - I was replacing rods and big ends anyway. Of note is that my slingers had slightly overflowed!! Probably explains the wear, but i've seen rods with the same wear marks from the cages where there was no slinger overflow.

Anyone know how much a rod can be honed without compromising the usable thickness of the hardening?
 
Quentin,

I have often found the interferance fit of the pins in the webs to be lacking, therefore I usually use new pins of 0.03mm oversize. When the rods are honed to suit, the big end diametre is increased by 0.02-0.03mm max, not enough to weaken the big end or harm the hardening.  But, this is often enough to remove most of the ovality and wear grooves.  Just fitting new rollers also usually requires a light hone to achieve correct clearances.

Although it would be nice to have perfectly circular big ends, a small amount of ovality is tolerable.  Let's face it, working cranks didn't contract that ovality last week, they've been like that the past 20-odd years without anybody noticing or being upset by it.

The cage wear grooves are a good indication of mileage and/or past maintenance. ::)  The alloy of the cage shouldn't really be able to wear the hardened race surface, it's solid deposits lodged in the alloy surface (once the anodising has worn off.  Zane big ends with their steel cages show no such wear!) that does the damage in the long run.  The grooves themselves are not the problem.  The groove edges can be... it is there where the rollers exert max pressure on the big end race, this is the first area to find irrepairable surface damage.  Same goes for the crank pins, the roller ends can damage the pins as well, even though the rollers used by the factory are nicely radiused!

I've found slingers filled right up to the entrance to the crank pin bore, effectively cancelling any filtering that might take place.

piet
 
Piet,

I have seen the aluminum cage wear the bearing surface. It's always on a engine that has not been run for years. The cage can oxidize from acids in the old motor oil and you now have aluminum oxide which is harder than the bearing steel. Does not always cause problems as it is usually not where the rollers touch.

Not a Laverda specific problem and on some Brit bikes with little clearance between the cage and the crank pin when new, the aluminum oxide can wear away enough to scrap the crank pin on what was still a good big end bearing.

If your gonna park the bike for years, change the oil first!
 
1200ts said:
Piet,

I have seen the aluminum cage wear the bearing surface. It's always on a engine that has not been run for years. The cage can oxidize from acids in the old motor oil and you now have aluminum oxide which is harder than the bearing steel. Does not always cause problems as it is usually not where the rollers touch.

Not a Laverda specific problem and on some Brit bikes with little clearance between the cage and the crank pin when new, the aluminum oxide can wear away enough to scrap the crank pin on what was still a good big end bearing.

If your gonna park the bike for years, change the oil first!
Click to expand...

I find this phenomenon on all Laverdas, irrespective of age or mileage.  Just more or less, depending mainly on maintenance schedules.  Bikes with low mileage must have had very long idle times by now, they show little wear.

The cages are supported to the rod big end by little ridges at the end of the roller windows, so that not the entire cage width contacts the roller race.  These ridges are seldom worn completely away, they can still be recognised on high-mileage cranks.

piet
 
BOETJE said:
Pin diameter  ? 36 mm  , Width of the rod big end is 30 mm.
Good luck : I believe many have tried...
Click to expand...

Yeeeessss......The diameters are not the problem - it's the width.  For those diameters 30mm is extraordinarily wide.

An engine of similar dimensions designed in the last 20 years would have big ends about 23mm wide.

At some point someone is going to have to commission a batch of cages. With CNC machines common now, it shouldn't be too hard.
 
GregT said:
At some point someone is going to have to commission a batch of cages. With CNC machines common now, it shouldn't be too hard.
Click to expand...

we have written the CNC program for the triple big end cages but not machined any yet as I still have quite a few spare cages in stock
just decided to get the program written just in case

 
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