palle
New Member
SR500, 2J4, 1978
Posts: 14
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Post by palle on Apr 23, 2007 14:33:51 GMT -5
Hi,
I am taking my motor apart to replace the cylinder head (sparkplug thread is gone...) and piston rings.
However, it did come up with some surpirses!!
On top of the piston it says 1,5 so I guess it is 1,5mm oversize? However, biggest standard Yamaha oversize is 1,0mm.
I guess it must be some kind of non-standard oversize piston (Wiseco?).
Also, the head gasket is made of 1mm thick copper!
How do I identify the piston type, so I can get new rings that fits?
Is it necesarry to use a new copper head gasket, or can I use a standard Yamaha gasket? Would that be compatible with the 1,5mm oversized piston?
Thank you for your help. It is highly appresiated
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Post by colinjay on Apr 23, 2007 17:25:15 GMT -5
Hi Palle,
You are correct, Yamaha pistons only go to 1mm oversize. I would suspect that you may have a WISECO piston fitted, as I have one in my spares collection and they are / were fairly coomonly available.
I would suspect that the copper gasket was fitted as a "performance" mod, which is / was common practice when fitting oversized / bigbore pistons to these engines.
CJ
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palle
New Member
SR500, 2J4, 1978
Posts: 14
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Post by palle on Apr 24, 2007 1:34:08 GMT -5
Hi Palle, You are correct, Yamaha pistons only go to 1mm oversize. I would suspect that you may have a WISECO piston fitted, as I have one in my spares collection and they are / were fairly coomonly available. I would suspect that the copper gasket was fitted as a "performance" mod, which is / was common practice when fitting oversized / bigbore pistons to these engines. CJ Hi, Thanks a lot for your answer. I think you are right about the Wiseco. I'll try if I can source some rings for it. Why would you fit a thicker copper head gasket for performance? I don't know much about tuning, but I would think you should fit a thinner gasket to increase compression (at least that was what we did in the "old days" to increase performance on our small 50cc bikes) ;D Do you know if I could fit a standard head gasket instead, or maybe even reuse the copper gasket? |
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Post by StewRoss on Apr 24, 2007 4:37:37 GMT -5
Hi Palle, Yes it could be a Wiseco for sure, they do make an 88.5mm piston. However there are a number of other pistons around as well such as Venolia, J&E, Arias, Protec, etc...are there any markings on the piston at all? Underneath etc? Different manufacturers may use different ring thicknesses...and ring types...If it is Wiseco you should be able to get rings fairly easily. Part number 3484XC... www.serco.com.au/pdf/WisecoPDF/WisecoSectionCOMP-screen.pdfYou could possibly re-use the copper gasket by heating it to cherry red a few times and cooling it under water...softens up the copper again. Can't recall how thick the standard gasket is but 1mm isn't real thick in any case... Anyone have a measurement for a standard one? SR  |
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lurch
Full Member
Posts: 217
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Post by lurch on Apr 24, 2007 13:44:04 GMT -5
Stew
Just measured the head gasket from my new "ATHENA" gasket kit
its 1.52mm
LURCH
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Post by StewRoss on Apr 24, 2007 22:08:31 GMT -5
Thanks for that Lurch, Ah so it possibly is a HC gasket then...the standard gasket would crush down a little...Palle I'd probably just heat soften it and re-use it again. SR |
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palle
New Member
SR500, 2J4, 1978
Posts: 14
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Post by palle on Apr 25, 2007 6:50:49 GMT -5
Thank a lot for your help. I have now taken out the piston, and here are some pictures: 4-f.dk/oben.jpg4-f.dk/seite.jpgOn top of the piston is says 1.5, but you can also see a 'C' stamped in to the crown. I hope someone can positively id it from this info? Thanx. |
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palle
New Member
SR500, 2J4, 1978
Posts: 14
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Post by palle on Apr 25, 2007 6:53:55 GMT -5
Thanks for that Lurch, Ah so it possibly is a HC gasket then...the standard gasket would crush down a little...Palle I'd probably just heat soften it and re-use it again. SR What is a 'HC' gasket? Well, I actually checked the measurement now, and it is 1,5mm thick and with a totally flat surface. I'll do the suggested heat treatment and reuse it. |
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Post by StewRoss on Apr 26, 2007 3:28:32 GMT -5
Hi Palle, Just my way of saving typing...high compression...have you got a pic of the inside of the piston under the dome? I'll compare it with a damaged 88.5 Wiseco that I have here...mine has a big hole in the top... SR |
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palle
New Member
SR500, 2J4, 1978
Posts: 14
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Post by palle on Apr 26, 2007 14:34:53 GMT -5
Hi Palle, Just my way of saving typing...high compression...have you got a pic of the inside of the piston under the dome? I'll compare it with a damaged 88.5 Wiseco that I have here...mine has a big hole in the top... SR Here is a picture of the inside. 4-f.dk/inside.jpgHope it helps |
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Post by StewRoss on Apr 27, 2007 3:00:56 GMT -5
Hi Palle, Mate I am still not 100% sure... Just by comparing the two pistons...yours and mine (with the big hole in the top)...it doesn't seem exactly like a Wiseco, (...there are some similarities in design)... Things like the oil holes don't line up with mine on the underside of the gudgeon bosses, the scraper ring oil holes are in a different place to mine, your piston has the relief for removal of the circlips mine doesn't (Wiseco's usually have spiral retainers that don't need the relief), the machining grooves on the piston sides above the top compression ring is not there on the Wiseco...etc...of course it may possibly be a Wiseco that is of a different design to mine... It is a forged piston by the looks of it at least...sorry I can't assist any further Palle. It could also be a J&E, maybe an Arias or a Venolia...etc. Good luck with the rings...if you still have them you could take the measurements and see what is around of the same dimensions to fit. SR |
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palle
New Member
SR500, 2J4, 1978
Posts: 14
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Post by palle on Apr 27, 2007 3:41:16 GMT -5
Hi Palle, Mate I am still not 100% sure... Just by comparing the two pistons...yours and mine (with the big hole in the top)...it doesn't seem exactly like a Wiseco, (...there are some similarities in design)... Things like the oil holes don't line up with mine on the underside of the gudgeon bosses, the scraper ring oil holes are in a different place to mine, your piston has the relief for removal of the circlips mine doesn't (Wiseco's usually have spiral retainers that don't need the relief), the machining grooves on the piston sides above the top compression ring is not there on the Wiseco...etc...of course it may possibly be a Wiseco that is of a different design to mine... It is a forged piston by the looks of it at least...sorry I can't assist any further Palle. It could also be a J&E, maybe an Arias or a Venolia...etc. Good luck with the rings...if you still have them you could take the measurements and see what is around of the same dimensions to fit. SR Ok, thank you for your help. |
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palle
New Member
SR500, 2J4, 1978
Posts: 14
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Post by palle on Apr 29, 2007 7:15:40 GMT -5
I have now measured the piston rings.
They are 1,00mm and 1,20mm.
Don't know if it helps any further?
Thanx
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