RG250 Big bore

[Sable]

Hi, I posted this in General Bike Ravings but I'm going to post this here too. I have a set of RG250 barrels on maximum factory oversize but there's still heaps of liner left, and I'm looking for any information I can get on bigger pistons. I hear things about RM125 pistons, but they only have a single piston ring, and I have a pair of TS125ER pistons (56mm vs RG250 54mmstd) but the piston pin hole is smaller. Does anyone know anyone who knows anything?

[koba]

Hi, I posted this in General Bike Ravings but I'm going to post this here too. I have a set of RG250 barrels on maximum factory oversize but there's still heaps of liner left, and I'm looking for any information I can get on bigger pistons. I hear things about RM125 pistons, but they only have a single piston ring, and I have a pair of TS125ER pistons (56mm vs RG250 54mmstd) but the piston pin hole is smaller. Does anyone know anyone who knows anything?


There are lots of catalouges available oin the net, add "Filetype: pdf" into your seaching and see how it goes.
Don't forget the piston pin height, and interactions with the ports. (eg. reilef area on side of piston and skirt shape etc.)

[RDjase]

Hi, I posted this in General Bike Ravings but I'm going to post this here too. I have a set of RG250 barrels on maximum factory oversize but there's still heaps of liner left, and I'm looking for any information I can get on bigger pistons. I hear things about RM125 pistons, but they only have a single piston ring, and I have a pair of TS125ER pistons (56mm vs RG250 54mmstd) but the piston pin hole is smaller. Does anyone know anyone who knows anything?

RGV are 56mm , and have two rings, i dont know if the gudgeon height is the same as rg tho, i have one at work i can measure,
what are all the sizes of your pistons?

[Sable]

Thanks RDJase. Turns out the wrist pin for the RG fits after all, even though the hole looks smaller. I have absolutely no measuring equipment, not even a ruler, and I am a novice to engine rebuilding/tuning. Attached are the two pistons I have, on left the RG piston, right the TS125.

[RDjase]

Thanks RDJase. Turns out the wrist pin for the RG fits after all, even though the hole looks smaller. I have absolutely no measuring equipment, not even a ruler, and I am a novice to engine rebuilding/tuning. Attached are the two pistons I have, on left the RG piston, right the TS125.

No worries, I will get the measurements and try and find out what the RG250 ones are, Google to the rescue lol,

www.rgv250.co.uk may have some info too mate

PM me if i dont post sizes for you, im fairly busy at the mo

[Sable]

The gudgeon pin feels looser in the TS than the RG, while stiff it is possible to rotate the pin in the piston. Perhaps get TS wrist pins and machine out the small end bearings ever so slightly..?

[Sable]

I found this (http://www.bitzforbikes.co.uk/1.50_O--Size_Piston_Kit_%2855.50mm%29-ref-525-508-289.html) but it's made by KHC and what little I can find on them appears to be complete shit. I'm not after performance, I'm just trying to resurrect a heap of crap.

[F5 Dave]

That sounds fine, old pistons get a bit tight, the bearing is the moving part so no drama.

I installed TS125 pistons in my X7 'back in the day' (oh dear, transformation into old duffer commencing). All good fun, & suzi stuff is often very similar (as the RG was to the X7) but you will need to be careful with the bigger pistons. You will need to give the ports some generous chamfers & possibly as the person doing the rebore to give you some lead in at the bottom of the bore if the existing one disappears with that large an oversize (just to ease slipping pistons in).

But then you come to the top end. Here you may find that the piston height is the same, but we will need to check that. The head gasket will likely be too small diameter & you may need to get a copper one made. Also the head may be too small diameter for the pistons if they protrude into the squish area, these may need to be opened up a little. They were 1 piece head yeah.

You will want to make sure you don't raise the compression too high. keeping a generous squish clearance will see to that. when together put some solder down the plug hole & turn the engine over & pull out & measure. You will want it to be somewhat over 1mm else the comm will be too high esp with the bigger bores. Don't want to stress that old crank.

If it has been sitting for a tickle more work I'd be keen to replace the crank seals. they get hard with age & any leak here will seize your fresh engine. They are cheap enough & remarkably easy to work on with horz split case.