RG150 power valves with oversize bores?

[pouakai]

I have just somewhat got to the bottom of a problem but that itself raises new questions....

I few months back I brought an RG150 for my son to complete his 6L upon, not long after we had it it seized and spat him off. Problem was a smashed limiter collar on the power valve which subsequently crashed into the piston and ground out the piston bore clearance to 0.5mm!!
We rebored the cylinder to 0.75o/s fitted a new piston, reassembled the power valves (replacing the broken collar) and tried again. Within 100km near seizure was evident again. I pulled the top the top end and found the piston badly rubbed with the ring grooves nearly closed over.
I looked for an explanation, oilways are good, oilpump was working, jetting is standard.
I had the cylinder honed and ring end gap is good and clearance is generous. It was a puzzle until tonight.
I put the new engine together yesterday gave it a run - nice down low but wont pull past 10K so first suspect must be the power valves aren't opening. I pulled the cables and went for a run manually manipulating the power valve cam. Power valves open I re-found the power above 10K so obviously I assembled something wrong, BUT with power valves closed I could feel the piston hitting the power valves !! So the cause of failure is found !!
So the questions are:
When one rebores what is the procedure for ensuring that the power valves are trimmed to clear the larger piston ?
Should the engineer take care of this ?
Should I just trim up power valves with a Dremmel tool ?
Should create new limiter collars for the power valves with shallower decent ?
Is there an after market collar for this situation ?
Is this only ever a problem when one goes past the factory O/S of 0.50mm ?

Once I decide upon a resolution for the above are there any gotchyas when refitting the PV drive cables ? I've done it right before but not quite sure how I got it wrong yesterday.....


P

[koba]

The description you give and the questions you ask convince me you will figure it out.

I mucked about with streetstock RG150's but never went that far oversize.

If I was having a go then I would have hit it with the dremmel but that would have been at my own risk.
I must also mention I have about 5 rooted RG pistons lying about the place...

I'd want to check it all with the head off and the cylinder torqued down to get an idea of the level and position of interference.

I'm not sure if 'oyster' still logs in here but he may have some helpful suggestions if he does.

[pouakai]

The description you give and the questions you ask convince me you will figure it out.

I mucked about with streetstock RG150's but never went that far oversize.

If I was having a go then I would have hit it with the dremmel but that would have been at my own risk.
I must also mention I have about 5 rooted RG pistons lying about the place...

I'd want to check it all with the head off and the cylinder torqued down to get an idea of the level and position of interference.

I'm not sure if 'oyster' still logs in here but he may have some helpful suggestions if he does.

Thanks Koba

It was always an issue that crossed my mind, I gave it a visual check for interference and it looked clear but in hindsight I should have measured it !

Oyster ? Yeah he still about although I think posting only when a thread really interests him. I paid a visit recently and it was with his sage advice that I rebuilt the power valves for the second time - they should be good for a while this time....Many thanks Oyster!

: )
P

[oyster]

A common problem is that the screws holding the power valves fall out but the motor keeps going ok. So what happens is the steel "stator" vibrates back and forth, wearing itself into the barrell. so when it's all rebuilt, with or without oversize, the stator can be up to 0.4mm further in, fouling the piston. To check, you must assemble all the parts and put a stright edge like a 150mm rule along the bore and using a feeler gauge confirm at least 0.2mm clearance to the stator and the moving parts. Yes, dremel, file whatever to carefully make fit. The crews should be replaced by grade 12.9 socket head screws, m5 x 16. Run a bottoming tap right down to the bottom of the hole. A touch of loctite and I have never seen a loo
se assembly again
I have seen many rg's that have had power valves touching, even broken off ones eaten away big time by the piston and the bike still runs fine! A lot of these have had a tidy up of the piston/ groove and back in service racing with no loss of performance.
If you are using a 0.75 piston, it's inevitable this is not genuine suzuki. Some aftermarket ones ares fine, but others are a complete waste of time as the alloy used has the wrong expansion rate. So the sieze without apparent reason. The only answer is to run them with big clearance but that means lost power, especially mid range, and they rattle like a concrete mixer. Hope this helps!

[imdying]

Just grind them back. I have an RGV with 61mm bores, Cougar Red CNC valves, and Stan Stephens stage 3 tune. They've all been ground, shaped and flowed to suit the (huge compared to 0.75) oversize increase, so big deal

When you put it back together, you'll want to set the powervalves at their open position, as the closed position matters not so much. Just rev it up, chop the power, remove the expansion chamber, stick your finger up the port and adjust the cables so it sits in the right spot. The closed and mid positions, you could care less about.