lonestar swingarm bearings, and help identifying stroker crank - Page 2 - Yamaha Raptor Forum
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post #11 of 18 (permalink) Old 09-02-2019, 01:55 PM
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A 4mm stroke will increase compression by .4 approx. So a 11:1 piston and 4mm stroker will yield about 11.4:1 total compression. Of course, this can be changed with the thickness of the base and head gaskets. I ALWAYS use a factory head gasket. 93 should be safe, maybe even 92 at sea level. If you're concerned about compression you could machine some of the 'dome' off the top of the piston.
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post #12 of 18 (permalink) Old 09-02-2019, 03:48 PM
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FYI, if your jetting is good for your intake and exhaust now, there is no need to change for any change to stroke, bore or compression.
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post #13 of 18 (permalink) Old 09-03-2019, 11:38 AM Thread Starter
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Originally Posted by DEZPERADO View Post
A 4mm stroke will increase compression by .4 approx. So a 11:1 piston and 4mm stroker will yield about 11.4:1 total compression. Of course, this can be changed with the thickness of the base and head gaskets. I ALWAYS use a factory head gasket. 93 should be safe, maybe even 92 at sea level. If you're concerned about compression you could machine some of the 'dome' off the top of the piston.
Awesome this is exactly the type of info I was looking for!!! I've literally searched for so many hours to no avail! I'm going to see what I can do to check out that stroker today I guess we'll see what I'm into lol

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post #14 of 18 (permalink) Old 09-06-2019, 03:20 PM Thread Starter
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ok so I finally got around to checking out the crank... turns out it's a +5mm it sets 2.5 above stock height (1.5mm above deck height, stock is 1mm below deck height) and exactly 2.5mm below the stock bdc... (87.92mm stroker/85.42mm stock) pictures attached!

I'm assuming I would need an offset piston for this, it came with a Ross 105mm and the top of the pin opening is 2.5mm higher than the stock piston, I'm not planning on running it with the stroker but hoping you can tell me about what compression that piston might be (pictured next to an 11:1 wiseco) I was thinking maybe 10:1?? that is the only time I've seen any mention of a Ross piston for a 660 he said it was a 10:1 compression 105mm (also hours of searching )

anyways I'm not too worried about the piston, as I was planning on a 102mm piston anyways to stay on the stock cylinder and not have to bore the case opening out... I might run it on a different build as a stock stroke 727, but idk... so my issue now is that the rod is rubbing ever so slightly on the case!! it's just enough to cause resistance and make a light light scratch on the case protrusion at bdc... the previous owners grinding is uneven on that portion of the rod, and it looks to be only rubbing on the one side, so I'm curious if I just keep it light and only take enough to make it clear would that be ok? and if so (or even if I have to trench? the case) how much clearance do I need in that one spot at bdc

thanks again!

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post #15 of 18 (permalink) Old 09-10-2019, 12:29 PM Thread Starter
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Originally Posted by DEZPERADO View Post
You would see the difference in the stroker pin being offset in the crank half's. But, be aware that a 4mm stroker will have the pin only 2mm difference. At BDC (bottom dead center) the piston is 2mm lower, and then at TDC (top dead center) the piston is 2mm higher, total of 4mm additional stroke. When mocked up with the stroker crank, stock piston and cylinder you'll want to check that the piston is at or slightly below deck height. If so, no spacer or extended timing chain is needed. Before final assembly it would be a good idea to 'clay' the valves to verify piston to valve clearance.
I keep reading this and thinking about what I'm going to do... I've been doing some more research and I can't find anybody that makes a 5mm stroker piston, so here is my thought...

I found a CP 11:1 +4mm stroker piston, if I do that I will be .5mm higher than stock, which should put me about .5mm below the top of the cylinder (stock with base gasket was 1mm below) and if I add an extra gasket (.25mm is OEM thickness correct?) that will put me at about .75mm below the top of the cylinder...

So even with an 11:1 piston If I'm only .25mm above the stock piston height there shouldn't be any clearance issues since I'm still .75mm below the top of the cylinder correct? Please feel free to correct me if I'm wrong lol...

But I am also going to re check my measurements when I get back home off the road just to double check my work and make sure I have the right numbers, even though I triple checked when I did it originally

Also if you or anybody else on here knows of any 5mm stroker Pistons out there I am all thanks!!

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post #16 of 18 (permalink) Old 09-10-2019, 01:36 PM
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Originally Posted by DEZPERADO View Post
Factory or aftermarket pivot bearings will fit your swingarm.

The crank is a little more complicated. It may be a longer stroke with a shorter rod and use a stock piston. Or, longer stroke and stock length rod and require a stroker piston OR a spacer plate under the cylinder and longer timing chain. You would have to mock up the crank in a case half, cylinder and piston. AND, check the bottom of the cases to see if some trenching (machining) is necessary.
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Originally Posted by MetalRox3 View Post
I keep reading this and thinking about what I'm going to do... I've been doing some more research and I can't find anybody that makes a 5mm stroker piston, so here is my thought...

I found a CP 11:1 +4mm stroker piston, if I do that I will be .5mm higher than stock, which should put me about .5mm below the top of the cylinder (stock with base gasket was 1mm below) and if I add an extra gasket (.25mm is OEM thickness correct?) that will put me at about .75mm below the top of the cylinder...

So even with an 11:1 piston If I'm only .25mm above the stock piston height there shouldn't be any clearance issues since I'm still .75mm below the top of the cylinder correct? Please feel free to correct me if I'm wrong lol...

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You originally said the Barker crank was a +4mm, why are you looking for a +5mm piston. But, as I said above, the "Barker may have a shorter rod, therefore using a stock piston". You should mock up your used parts to verify compatibly.

Yes, you can stack base gaskets, be sure to use sealer between each to prevent sliding, but that may make the timing chain to tight. I don't remember the deck height on a Raptor, but on Honda 2 strokes I would shoot for 0.050in, (Piston below TDC).

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post #17 of 18 (permalink) Old 09-10-2019, 02:14 PM Thread Starter
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Originally Posted by DEZPERADO View Post
You originally said the Barker crank was a +4mm, why are you looking for a +5mm piston. But, as I said above, the "Barker may have a shorter rod, therefore using a stock piston". You should mock up your used parts to verify compatibly.



Yes, you can stack base gaskets, be sure to use sealer between each to prevent sliding, but that may make the timing chain to tight. I don't remember the deck height on a Raptor, but on Honda 2 strokes I would shoot for 0.050in, (Piston below TDC).
hey I originally said +4mm cuz that's what the guy told me but after measuring it turned out to be +5mm with a stock length rod... I didn't quote you maybe that's why you didn't see it, I'm still learning lol... but check my previous post I took pics and measurements with a mocked up stock cylinder gasket piston, and both stock and the stroker crank...

That is why I was asking if you or anybody else can tell me about the +5 stroker piston so I don't have to worry about stacking gaskets or adding spacers etc...

thanks

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post #18 of 18 (permalink) Old 09-10-2019, 02:52 PM
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Originally Posted by MetalRox3 View Post
ok so I finally got around to checking out the crank... turns out it's a +5mm it sets 2.5 above stock height (1.5mm above deck height, stock is 1mm below deck height) and exactly 2.5mm below the stock bdc... (87.92mm stroker/85.42mm stock) pictures attached!

I'm assuming I would need an offset piston for this, it came with a Ross 105mm and the top of the pin opening is 2.5mm higher than the stock piston, I'm not planning on running it with the stroker but hoping you can tell me about what compression that piston might be (pictured next to an 11:1 wiseco) I was thinking maybe 10:1?? that is the only time I've seen any mention of a Ross piston for a 660 he said it was a 10:1 compression 105mm (also hours of searching )

anyways I'm not too worried about the piston, as I was planning on a 102mm piston anyways to stay on the stock cylinder and not have to bore the case opening out... I might run it on a different build as a stock stroke 727, but idk... so my issue now is that the rod is rubbing ever so slightly on the case!! it's just enough to cause resistance and make a light light scratch on the case protrusion at bdc... the previous owners grinding is uneven on that portion of the rod, and it looks to be only rubbing on the one side, so I'm curious if I just keep it light and only take enough to make it clear would that be ok? and if so (or even if I have to trench? the case) how much clearance do I need in that one spot at bdc

thanks again!

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With extra gaskets or spacers I doubt you would get a stock timing chain on, and a extended chain would be needed. There is a compony that makes thicker, copper, reusable gaskets, any thickness but I can't remember their name. You could machine the top of the piston but that may compromise the top ring land. Also the head could be machined to allow the piston to go higher, again compromising strength. Best option would be a stroker piston.

You would definitely have to take a Dremel to the case and allow extra room for expansion/contraction and 9,000 RPM's.

I'm not a expert on piston domes but I would suspect that's at least 12 or maybe 14:1

This may be a long shot, but Daniel at Cuervo Racing has been in Raptors for a long time and may have some insight of what works and where to get it.

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