BIG Big Bore Kits For Minarelli Engines?

BIG Big Bore Kits On A Minarelli

Some time ago I saw 52 and 54mm big bore kits advertised to fit minarelli engines. It said they may fit with no case clearancing, so I had to give it a try. I'm sharing what I learned to save anyone else some trouble. Long story short : Stick with 47-48mm bore kits for 49cc mianrelli engines unless you want to split the cases and have them bored to fit a larger cylinder. If you are lucky enough the own the 90cc minarelli engines 52 and 54mm cylinder kits should work. Even then you will need to be sure you get the kit intended for the proper stroke. There are kits made for various sizes of crankshafts. Do your homework so you don't waste your money.

I installed the 52mm piston without even checking for case clearance. The first thing I should have done was check for cylinder/case fitment. Unfortunately, not riding for a long time causes me to do stupid things. I jumped into it in anticipation of riding. Don't be like me lol. Anyway, on with the show....

Here's the MRP 52mm cylinder kit.


I start by installing the rings on the piston. Here's what I used.


One side of each piston ring should have letters, a dot, or some sort of marking. This marking must face up. There is no pic of the markings on these rings because my camera sucks and doesn't like to get too close.

This style of piston has one peg in each ring land that locates the ring. You must be sure to position each ring around it's pin.


I am using a ring tool, but it is not necessary. Just be careful not to twist or break the piston rings using too much force. Put both rings on gently and make sure they are seated in the ring lands properly.






Now that the rings are installed on the piston, I was ready to attach the piston to the connecting rod. Here are my piston/rings, wrist pin, wrist pin bearing, and circlips.


Now I lubricate the wrist pin bearing with 2 stroke oil and insert it into the connecting rod.




Now I install one circlip into one side of the piston. I use needle nose pliers to position it. This can be a pain until you get used to it.




Now lube the wristpin with 2T oil and slide it partially into the piston on the side without a circlip. Make sure you are installing your piston with the arrow facing the exhaust port, then line the wristpin up to go through the conecting rod/wrist pin bearing. Push the pin through and install the other circlip.




Now I installed the base gasket. This is when I realised I had a problem. In the picture with it installed, you can see how far off it is. I then realised the piston wouldn't even fit into the case, let alone the cylinder. Oh well.