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Low Compression

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Replied by Swoop56 on topic Low Compression

Another think you need to check .
Wiseco used to run greater piston to cylinder clearances than stock yamaha pistons .
Modern Wiseco's may run a closer tolerance than old style .
You need to find out what clearance Wiseco specify , to properly verify where you sit .
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21 Jul 2021 14:06 #21

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Replied by RT325 on topic Low Compression

Just had a thought--rare moment. If the rings were stuck in the grooves--& sounds like they were 'really' stuck from what you say--is it possible someone has used yamaha tapered rings in parallel grooves of the wiseco piston. Normally with no running "i think you said" they shouldn't be stuck or anything like stuck. & yes i forgot, wiseco run extra clearance by a little bit.
21 Jul 2021 14:46 #22

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Replied by MarkT on topic Low Compression

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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21 Jul 2021 16:15 #23

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  • Shauno
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Replied by Shauno on topic Low Compression

The rings are defo not tapered; they are parallel.
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22 Jul 2021 00:48 #24

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Replied by Swoop56 on topic Low Compression

Like RT 325 , I'd be a bit concerned about why the rings were stuck in the ring lands ,
when you haven't even run the motor .
Can you quote the Wiseco numbers for both the piston and rings .
Another query . The piston that you replaced . Was that also a Wiseco , or OEM Yamaha .
If you can also quote any numbers on the crown , it might help with identifying your problem .
22 Jul 2021 05:07 #25

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Replied by DT400FRANK on topic Low Compression

Rings will get stuck when an engine sits and the fuel and oil drys up and gets sticky. I had to boil an 50cc  two stroke Indian piston in oil one time to get the rings to come loose but they had lost there tension from being compressed and boiled. :)
22 Jul 2021 05:18 #26

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Replied by Shauno on topic Low Compression

Wiseco STD piston 85.5mm    75-78 232MO8550


Piston details
22 Jul 2021 06:11 #27

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Replied by Shauno on topic Low Compression

PS. just retested my compression with a new gauge as I broke my old one; and its now up at 130psi and that's with the decompressor disconnected. The bike now starts and runs OK; I've listened for piston slap and well not too shabby; I'm still gonna strip the head and barrel off and measure the jug properly though. However I now have a new challenge. The bike runs for about 30 secs and then dies. If I let stand for a while she will fire up again and do exactly the same. My thinking is that it running out of juice and maybe I've got the float setting wrong? any advice on how to set the float height correctly? or could there be another issue?
22 Jul 2021 06:19 #28

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Replied by DT400FRANK on topic Low Compression

Check compression right after it dies. Make sure you have a good flow of gas going to carb. I was working on a customers lawnmower at one time and it would loose compression after it warmed up and it would die. Possibly could even be the ignition coil breaking down. 
22 Jul 2021 11:49 #29

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