GPR Camp: Replica Racers

I am building a Derbi race motor. I pulled the donor motor apart and have determined that the timing side is stepped with a woodruff key. I ordered a Malossi crank. They offer one with the tapered end and one with the stepped end. I purchased the one with a stepped end (Malossi #5312590). I have now pulled the motor apart and am preparing to reassemble it. However, I don't know whether the Malossi crank is balanced to run with or without the OEM internal balancer shaft. My motor is marked "SendaH".

I have asked Malossi, but am not receiving an answer. Does anyone know the answer to this question?

You want to run with a balancer. It makes the engine smoother. From what Remi discovered there are even custom balancers out there. I have a post on here somewhere about how to set things. I’ll see if I can find it and link it.

Yup here you go: How to balance a GPR Engine.

I think on a race engine it should be left out. I didnt put it in either, altough its a different engine. You sould balance the crankshaft out anyway before assembling it. If you put in the balancer you will lose a bit of a performance. On the street its not that important but on the track, it is very noticable.
If you want to race, balance the crankshaft and leave the balancer out
If you want to go on the streets, then put the balancer in.

Crankshaft Malossi RHQ référence, ONLY for €2 GPR motor With balancer:

5312590


Crankshaft malossi RHQ référence, for derbi senda €2 :

5312320


The better for a race engine is a derbi GPR engine ( whith balancer)

Caution!!! A balancer is not possible in derbi senda crankcases ( or whith machined )

Very interesting!

My motor (that I bought from a guy for $100) is Marked "Senda H", so it presumably came from a Senda. It has both a mechanical tach drive and an internal balancer shaft.

I'm gonna leave the balancer in and see how it runs on the dyno.

Thanks for taking the time to help me out!

See you at the track!

My mutiples crankcases GPR are notified « SENDA H »