Low compression question

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27
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Location
Chicago
Water Crafts
00 FTC rfi
99 gp800
#1
Is it possible to get a low compression from a weak battery?
Long story short I need to rebuild my gp800 and a guy is selling one super cheap that revs out of water but only 2k in water. Changed plugs but didnt make a difference. I'm thinking of buying his and taking the parts I need but will test his ski with my battery if that could be it.


Thanks in advance!
 


etemplet

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Louisiana
Water Crafts
1996 SPI, 1996 GTX, 1997 GTX
#2
Charge the battery and do a compression check as you say. Usually the engines spin over pretty easy with no plugs installed. If the skis doesn't revv in the water certainly compression is a concern. Then again, good compression readings don't mean the cylinders and rings are healthy. I got 145psi on a cylinder that had half the bottom ring missing.
 

mikidymac

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Water Crafts
2003 GTI
2001 XP
1997 GSX
1996 XP
1996 HX
1996 SPX
01' Superjet
#4
Keep in mind the Yamaha 800 has plated cylinders so you can’t just bore them oversized for new pistons.
 
Messages
27
Likes
4
Location
Chicago
Water Crafts
00 FTC rfi
99 gp800
#6
Keep in mind the Yamaha 800 has plated cylinders so you can’t just bore them oversized for new pistons.
Yeah I got quoted 200/ea cylinder with replating... but I'm sure I'd end up needing a new piston too.

All the refurbished engines seem to be sleeved...
 

mikidymac

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Staff member
Moderator
Messages
8,548
Likes
540
Location
California
Water Crafts
2003 GTI
2001 XP
1997 GSX
1996 XP
1996 HX
1996 SPX
01' Superjet
#7
Yes the refurbished ones are sleeved which makes them run hotter. Yamaha intentionality plated the aluminum for better heat transfer.

Either way you will need new pistons and rings so that isn’t a factor.
 

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