Aprilia SR 49 to 95cc

[2strokd]

In the middle of a mild street build and thought ide share. I have some pics but i think my son took the camera, will post later.
Its a 2000 Aprlia SR50 with a LC carbed Minarelli engine. The build will have a 42mm stroke crank with the OD shaved down to fit the small Aprilia cases. We are using a 54mm bore iron cylinder.

i639.photobucket.com/albums/uu112/190mech/rs50-965_zpsfa0c8647.jpg

i639.photobucket.com/albums/uu112/190mech/rs50-966_zps2cad5049.jpg

i639.photobucket.com/albums/uu112/190mech/rs50-967_zpsad31df02.jpg

We opted for a better ProX 85mm connecting rod with a 42mm stroke. At first i planned on using a 45mm stroke crank but the cases proved to be too thin for this. More on that subject....

"Here is an update on Robert's Aprillia RS50 stroker build.We've been spoiled by CPI cases!Robert sent me the cases to bore for the Carlos 45mm crank,I measured them,NO WAY!!These cases are 3mm thinner OD than the CPI stuff(87.1 - 90.1). checked the CPI case OD to the Polaris ATV case,,same OD..Got to looking at alternative cranks,Carlos has a 45mm/10 pin shaft thatll drop in,but we'll have to change the rod for a 12 pin($$)..Then I found out a 50cc crank uses a 16mm big end pin and the 90 stuff uses a 18mm pin,crap!That complicates it more..ProX has a rod kit for the 18 big pin,85mm length,12 pin(03.2002),and they have a 16 big pin,85mm length,12 pin(03.2008)..After a bunch of phone calls we decided to go the cheap route(as always),,Have a Polaris crank ordered($35) and will turn the crank wheels down kinda like Brent's 90 motor and press in a ProX rod kit,that way we'll have a 96.19cc build wedged in the skinny Aprillia cases,,Hope it works!!"

Sometimes even when you "think" you have done your homework and you know an engine something will bight ya!

I have the port matching and trench work about done. Pics and more info to come.

[moofus02]

Good stuff lots of info. Makes me wonder about my 05 Zuma motor and how thin the cases are and what crank is in it. It's 45mm x54mm hope it doesn't break in two

Sent from my SPH-L720 using proboards

[2strokd]

Ide love to know what the OD of your crank wheels are? Do you know what crank is in it?
I have a set of Zuma cases and they are the same as the Aprilia, very thin! After seeing the CPI and FM style Minarelli i would choose either one of those over the Aprilia or Zuma cases.

Here is a pic of a stock CPI case half next to a Zuma one for reference.
Look how much less meat there is on the Zuma compared to the CPI

Zuma left CPI right


I think you can get away with this style crank but pistons are not out there anymore.

www.ebay.com/itm/331075512866?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

I have this one and it wouldnt fit in the Aprilia cases.

www.ebay.com/itm/231104867982?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649


Very interested in what you did to get it all to work out.?

[2strokd]

Sorry, i see you dont know what exact crank it is.

[moofus02]

I was going to get that second crank for another motor but can't find them anywhere now. I bought this motor togather and don't know what it is. Guy told me it was a Taiwan kit and crank. I'm really curious to see what it is also. Real tempted to split it to find out

Sent from my SPH-L720 using proboards

[2strokd]

Most all my before pics are gone or i cant find them. Here is what i have now. I will fill in more if i find them?

Engine before any work.



Engine torn down and bored for stroker crank and much bigger 54mm cylinder.




Port matching to the base of the cylinder and making a small trench, or flowpath.

[moofus02]

If a person wanted to build a big motor for a Zuma the adly moto 90 cases are the same length as a Zuma just the shock Mount is farther back like the longcase clones and all the big stuff drops rite in. Just can't get a belt for the overrange and the belt cover is adly specific. I've got a set of cases on the floor I need to build up

Sent from my SPH-L720 using proboards

[2strokd]

More pics of the Ape build.








Got the cases cut and shaved pretty nice. I dont like that what looks to be an oil galley in the trans tunnel but it will have to stay for now as time nor budget is allowing it to be filled

[2strokd]

The bottom pic is me cutting the skirt off. A hose clamp kinda helps me keep a straighter cut.
All is filed and smooth in the end.

[nelson]

Very nice work! Are you going to run that technigas pipe that came on it? Looks like the same one I have, I saw plans for a custom built pipe in your pics

[190mech]

Lookin Good!Ya got him a bigger Del carb?Might need some mo-better reeds too..Stock iggy?

[2strokd]

We are using one of Johns Peace Pipes on this one. Big long mid belly section with a long "kick stand" header. Should work out well for this one on the streets!

21mm PHBG carb with some CF reeds in the stock cage for now. Stock ignition.
Intake is still up in the air? It had a very tight fitting small intake and carb stock and i am not sure i will get the 21mm and a better intake to fit and still get a hose for the inlet on?
I might need to go "rear face" with it all?
One nice thing about this build is no time crunch! Ive had it plenty long enough though, so ide really like to get it buttoned up soon.
It still needs taller final drives and money for any type of rear facing carb. But for now my major concern is using the parts i do have

[2strokd]

I dont see it in the pics, or i fixed it that well but man, i had the dremel take off on me once when my hand cramped and i thought i had all but fookered up the mating surface to the cylinder case base . Thankfully its ok. A bitter sweet reminder of just how easy it is with a good cutter!

[2strokd]

More work on the Ape.





Opened up the "scallop" cut for the boost trans and matched it all best i could.











With the supplied base gaskets i was getting around 180/120 degrees duration. I took the thinner gasket and swapped it for a thicker one i had to get almost 5 more degrees duration. I think this will be a good start for this build. I dont know the squish number yet but it looks close according to the piston at TDC.

[2strokd]

Bearings are in and i am about ready to pull the crank out of the ice box and seal this puppy up!