MHR bored and stroked

[LMH]

So I burnt up my piston for my MHR race cylinder and instead of putting another MHR piston and rings in for 90 bucks, I bought the Wiseco 47.5mm piston for the yz80 off of a guy on another forum. I think the kit number is 477p2, but when I search it its hard to find anything relative.
It is a little taller than the malossi, so to make up for this I plan on stroking it. Has anyone done this yet? Or at least stroked a MHR race cylinder? Its going to be interesting, I will do it on a spare block I have sitting around and try it out on a stretched and reinforced 89 elite. I need an extra long throttle cable and a 28 MM carb now.
For everyone running CHT gauges, make sure they seal, I learned the hard way. I did a pressure test before installing it, not after, too lean for a 122 jet and a big air leak.

[LMH]

Wiseco specs from a pdf
displacement 81cc
bore 47.5mm
oversize 0.02"
piston MS 416-4772
Piston MFG # 477M04750
---Specs from the seller---
47.5mm
12mm pin
54mm tall
21.5mm pin to dome
21.5mmpin to skirt

[kingkamehameha]

Throw it away you already ruined the whole
Bore. Also you can only ministroke it wich is a bad idea

[Red Eft Performance]

There is a very good chance the cylinder is still good. The lining in these cylinders is very durable. If cylinder is still good just get new malossi piston and try again.

[LMH]

The cylinder is good for sure. It only melted a little of it on it, no scoring just melted aluminum. As soon as it hit 390 something I shut it down but it was too late, I started it up and it felt weak so i shut it back down. I just dont want to spend another 90 on a piston if I can just use a better piston. It seemed as though the piston is the same one used in the normal malossi cast kit. I have a corsa also and that piston is extremely nice.
Is it not possible to bore this cylinder? What option do I have for honing it if not also? I would just let the machine shop do the honing and chambfering after boring I figured.
This piston will work with a spacer or multiple gaskets and shaving down the piston skirt its not far off. If I end up just honing the MHR I will save it for a different 47mm kit that I have and do it with that one I suppose.

[veedubh20]

main is too small. go 140 then work down out

[LMH]

Ya I know that now for sure, everyone said 122 was going to be too rich. 135 is probably what it should have been, I knew better.

[Red Eft Performance]

The cylinder is good for sure. It only melted a little of it on it, no scoring just melted aluminum. As soon as it hit 390 something I shut it down but it was too late, I started it up and it felt weak so i shut it back down. I just dont want to spend another 90 on a piston if I can just use a better piston. It seemed as though the piston is the same one used in the normal malossi cast kit. I have a corsa also and that piston is extremely nice.
Is it not possible to bore this cylinder? What option do I have for honing it if not also? I would just let the machine shop do the honing and chambfering after boring I figured.
This piston will work with a spacer or multiple gaskets and shaving down the piston skirt its not far off. If I end up just honing the MHR I will save it for a different 47mm kit that I have and do it with that one I suppose.

The piston that comes with the MHR is NOT the same piston that comes in the cast kit. Honestly Your not going to find a better piston than the piston that comes with the kit. An air leak/detonation will melt any piston you put in it. If you mini stroke it you are going to mess up the port timing and it wont perform as good as stock stock. Just my suggestion. Keith

[LMH]

Thanks for clearing that up, can you post pictures of both pistons for me? I keep seeing a different style head than the one I got from you for this MHR kit every where I look. This head doesn't have a high temp coating like them, Im not concerned as much as confused. I know you where going to call them and ask but I haven't hear back from you about it.
Ill get some money to my friend and Ill order another piston from you, but whats the best solution for cleaning up the aluminum cylinder? With the old cast iron malossi I just used a flex hone and called it a day, that engine is still running great. The replacement piston and rings for that was only $48 from ebay. I may have found the same piston for this MHR for $70 also but who knows about what and when Ill get it. I leave for home in 2 weeks, do you know when it might arrive?
I ordered another Polini Corsa from Daywot for $292.50, when I get it I will take pictures this time side by side of the MHR vs the Corsa, the cylinders at least... I don't know if Patrick from Daywot will give you that kind of deal but $293 shipped is the best price Ive found for them so far, it cant hurt to ask. Hes who I got my first one from for 325, I put that on an elite and sold it to a friend for $1200, who still flogs it daily. You can floor it non stop and it loves it.
So I guess I will try the new piston from redeft first and if all else fails Ill weld that bore to the piston and make a MHR ashtray out of it, a $330 ashtray.
Also to add, I do air leak pressure checks and compression checks before installing any 2 stroke engine. Its just too easy to do. Not positive but I think I had an air leak through my CHT sensor, but I do know it was extremely too small of a main for 10k+ rpms also.

[Red Eft Performance]

Here is pics of corsa and MHR viewtopic.php?f=16&t=19815