Motoforce racing cylinder defective batch?

jusspb

Well-Known Member
Hellou, has anyone had problems with that cylinder? Minarelli horisontal.
In Estonia, there are some cases, that It breakes the crankshafts small-end bearing. First scooter drove 170km and second one 220km, and the small-end bearing was powdered.. All parts were brand new and put together by a professional. This has happened with 12mm gudgeon pin.
 
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melf #50

Well-Known Member
we race with a Motoforce racing cilinder , we have no problems whatsever...

what is de brand of the crankshaft and the needle bearing?

what kind of oil and how much do you use? what squish do you use?

what RPM , exhaust etc. etc.?
 

jusspb

Well-Known Member
one scoot had endurance crankshaft and bearing and second 1 had motoforce.. this didnt happened with 10mm gudgeon pin..
Dont know other data..
But they drove ~200km.. so pretty low rpm, cause they were running in..
Oil was fully synthetic.
Other parameters dont matter i think..
Cylinder were bought in winter.. so maybe 1 batch of faulty stuff?
my quess is that gudgeon pin is littlebit smaller, and just rammed the small-end bearing until it was powder or smth..
 

Aidix

Well-Known Member
Check the sideways clearance for the smallend bearing. The opening in de piston varies from time to time. Sometimes way too big and the bearing can slide from left to right.
 

Areomyst

Scootin' America!
I'll be building one with this cylinder soon. Everything looks top notch, and I haven't heard any complaints about it.

I've seen a lot of Chinese small end bearings break very soon.

~Josh
 

melf #50

Well-Known Member
a good crankshaft is thick (smallend) , sometimes some brands make the smallend very small , what wil cause problems..

if you use a Polini evo 70 , Hebo manston racing or cilinders like stage6 racing with 12mm pin you'd have the same problems..

if the needle bearing breaks then that bearing and/or crankshaft is just not suitable for this piston...

simple as that..
 

jusspb

Well-Known Member
we quess we found our problem..
Pistons were faulty ones..
I had a mistake.. thsi happened with 10mm gudgeon..
The professional, who had MF racing on rox, had same problem.. with 10mm. But he replaced the piston to 12mm before blowing up..
And then he saw, that gudgeon or bearing was eaten from 1 side..
and bearing was holding on 1 side..
Now he is going to get those 3 pistons measured.. and then send back to SA.
 

waxhead

Member
I have raced with this cylinder and its a great thing.
I have had it let go in the bearing as well. it was to narrow a bearing and it was moving on the gudgeon ( sideways)
The bearing sizes should be a std size and the pistons made to accommodate that but they dont
 

Areomyst

Scootin' America!
I have raced with this cylinder and its a great thing.
I have had it let go in the bearing as well. it was to narrow a bearing and it was moving on the gudgeon ( sideways)
The bearing sizes should be a std size and the pistons made to accommodate that but they dont

Isn't the wider Stage 6 bearing recommended with that setup anyway?
 

Aidix

Well-Known Member
S6 wide bearings don't fit anymore, pistons were changed already over a year ago.
If you have some dusty old kits it does fit.

Newer kits also have HUGE bevels on all ports, about 1mm wide. Looks rediculous but I'm sure al 16 year olds like it.
 

Areomyst

Scootin' America!
S6 wide bearings don't fit anymore, pistons were changed already over a year ago.
If you have some dusty old kits it does fit.

Newer kits also have HUGE bevels on all ports, about 1mm wide. Looks rediculous but I'm sure al 16 year olds like it.

The one I got last month must have been an older one then I suppose. So far it hasn't had any bearing problems. The owner seems quite happy with the performance. :)

Ciao!

~Josh
 

waxhead

Member
How good are those motoforce cylinders
I love them , its my cylinder of choice for a street bike
I love to put the city 16 on them and they pull real hard for a scooter
 
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