sv emulator fork oil quantity, and single ring on prox pisto

Technical questions and answers

sv emulator fork oil quantity, and single ring on prox pisto

Postby paul g » Thu Jan 14, 2016 11:06 pm

Firstly sorry to bombard the forum with Newby questions but I can not find the answers anywhere else!
My tzr race bike is fitted with sv emulators, I have a leaky fork seal and wondered how much oil should be in each fork and what grade please?

Secondly I removed the top end today and noted I have prox pistons but only running the top ring, is this ok?
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby Higgsy » Fri Jan 15, 2016 10:30 am

Hi Paul, it used to be a trick to use just one ring, the idea is to cut down on friction. Personally i don't think it makes much difference having two rings on the piston and with one ring I reckon it will wear more negating any friction advantage. Just my opinion of course, but i'd be examining the pistons and at least re ringing them anyway.

The emulators in theory take a little air gap up, but it's fairly minimal. 444cl and 10wt I would have thought. With the emulators the fork oil weight controls the rebound damping and the emulator the compresion damping. If you feel it needs more rebound damping i.e. the forks are coming back to position too quickly, then go up on the oil weight
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby paul g » Fri Jan 15, 2016 11:13 am

Thanks Higgsy great info....
Also noticed its running 2 base gaskets on each, when measured together they are about 1 mil in thickness

Going to take the top end over to pat seagers in Ipswich to inspect and measure up clearances. Any one else used him on here?
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby Higgsy » Fri Jan 15, 2016 11:09 pm

Oh yes, we know pat very well :lol: lol
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby Denzil » Fri Jan 15, 2016 11:20 pm

Higgsy wrote:Oh yes, we know pat very well :lol: lol



Just make sure you have a spare 2 hours when you go, he likes to talk :lol:
He knows his onions though
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby Higgsy » Sun Jan 17, 2016 4:29 pm

2 hours. Blimey you were lucky, had him on the phone for longer than that :shock:
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby Malc » Sun Jan 17, 2016 5:43 pm

Higgsy wrote:... having two rings on the piston and with one ring I reckon it will wear more negating any friction advantage.

I don't think one ring wears quicker - after all, the single ring is still covering the same "distance" as one ring of a pair has to. Definitely agree on the reduction of friction though, and more, when you consider only one ring is "scrubbing" the cylinder, there is less wear on the cylinder wall too. The benefits of one ring over two it would appear are several. The downside is of course the potential loss of compression as there is only one ring end gap - any gasses escaping past this won't be caught by the second ring. But then again, as the end gap shouldn't be any more than half mil, losses are minimal.

Just my take on one versus two...
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby Higgsy » Sun Jan 17, 2016 7:19 pm

I can see the argument for one ring Malc. Certainly there is a heat and friction disadvantage with two. We all use either Mitaka or TKR pistons with RIK rings, they always seem to be well over the minimum ring gap, at least the ones I've fitted have, so having two should increase the seal against the piston wall and decrease the amount of blow past. In fact another old trick, particually in the lc days was to use a ring set.25 over the piston size to enable the ring gap to be filed to perfection, I do wonder if the ring in this case could 'bulge' into the port though.

I still think one ring will wear more than two. My reasoning: One ring mx pistons are supposed to have their rings changed every meeting to retain optimum performance for instance, the ring is getting battered from both sides, it gets hit from the top by the combustion process then whacked from the bottom by the intake charge. Having two rings must help the longivity of the components by sharing the load so to speak, and therfore keep optimum performance over a longer period. Agreed it's travelling the same distance, but I think it has to work harder to do it. The ring to bore seal, and that's what we are trying to achieve to get good power must be better with two rings I would have thought, particually with a cast liner

One reason why I personally would always run two rings on a TZR is the pistons have a habit of dropping the ring peg down the exhaust port, in my mind anything you can do to minimalise this would seem a good idea, it's the rings fluttering against the peg that wears it until it falls out, I reckon there would be less ring flutter with two rings. Although i guess you could argue that two rings have twice the chance of doing this, I've never personally seen a bottom ring peg let go, possibly because it flutters less and runs cooler? (que YPMer telling me theirs has let go :roll: )

Saying all this, proper two stroke race bikes generally only have one ring, as do top end 2t mx bikes, but the maintenance shcedule is far more intensive than we do with the TZR

My conclusion: Although I'll conceed there is a friction disadvantage in running two rings, I think that would be offset by better compression over a longer period, unless you can get the single ring gap down the the absolute minimum. I've done near enough four seasons on my barrels and you could still see the original honing up to the last rebuild, so although i can see the argument for less wear with one ring it seems that the rings wear more than the barrel.

It's an interesting technical argument, anybody else got a take on it?
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby tzr_andy » Sun Jan 31, 2016 4:13 pm

My take is that racing two strokes are designed to be maintained almost hourly, whereas the pistons we use are designed for road use (i.e. changing every 10,000 miles or so). So...does that mean using a single ring and then doing the normal maintenance...I'm not sure. I've always run both rings and the spring washer underneath the scraper ring to ensure everything is as it should be.
The advantage to using two rings is that there is more in contact with the cylinder wall, and it probably provides a bit of support to the piston skirt as it touches the wall during the stroke. Notwithstanding reduced friction, I think that there is likely to be some heat transfer from the piston (low thermal mass compared to the cylinder) which can only be a good thing.
My view is that the marginal gain from this (and arguably other modifications) 'could' make a difference, they are likely to be offset by the quantity of lager and junk food consumed the night before most races, and are likely to make the bike more susceptible to mechanical gremlins. Keep them relatively standard, without super tight head clearances, or aggressive porting and on sensible jetting and its likely to run for longer and not break down. As someone once said...'to finish first...first you have to finish'.
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Re: sv emulator fork oil quantity, and single ring on prox p

Postby paul g » Sun Jan 31, 2016 8:32 pm

Pat Seeger phoned me about my top end Friday...

He told me my pistons were still in A1 condition and bores were good just needs a hone, clearance will be a tad over 3thou which he said is fine for this engine and would be a waste boring to the next size at this stage,on the ring front tho, he said they were worn and needed changing, he recommended fitting both top and bottom ring but leaving out the expander, so with his advice this is what I have opted for...

On another front I picked up another bike last weekend in boxes, was going to use it as spares, however upon unpacking I found it in such nice condition iv been building it back up, the engine is fitted with some rather nice f3 parts , it has f3 crank,f3 ignition, f3 cdi,f3 expansion chambers, f3 rev counter, f3 carb kit. Top end is graham file tune.... its not been ran for a few years so may be taking this to Pats to look over
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