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Discussion Starter · #1 ·
Just finished the top end rebuild in my 05 600HO today - used SPI piston (single) ring kit. Sled fired up great after a few pulls for the first time and I was stoked - sounded good!

However, compression (engine warm) was somewhat lower than I would have expected (about 130 PSI) both sides - this was slightly lower than before the rebuild when the sled had almost 7,500 miles on it! Initial compression prior to rebuild was about 140 PSI both sides - all factory original pistons, etc.

Obviously, was slightly dissapointed in the new compression reading. Is this just due to rings not being seated yet, or is something else going on? any suggestions?

(* Note: I just realized that my compression reading was without the throttle wide open - does that really matter?)

Thx,
 

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Discussion Starter · #3 ·
Did not do anything special to cylinders... they looked mint! Cleaned them up and lubed them with some mineral oil prior to setting them over the new pistons/rings. Also checked ring clearances prior to assembly and set end gap to .016.

What is involved in deglazing? and is it too late to tear it back down and do that? Is it required for cylinders that already look really good. I followed some of the DIY walk throughs in the FAQ area of Dootalk and none of them mention the "deglaze process."

New to this as it is my first rebuild and I thought it went pretty smooth - your help is appreciated.

Thx,
 

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Well. Deglazing involves a trip to the machine shop. They use a special hone on the nikasil coated cylinders. not to go back on what i said before, but u might not need to. If comp test b4 rebuild was around 120 or lower i'd be concerned. Something else isnt right. I'm not overly familiar with this new of a motor so hopefully the experts on here can help.
 

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It will come up with some use too, the rings seat after a couple runs. As long as the compression is the same on both sides you are good. Unless you have a high end (snap on) compression tester, most of them are not very accurate and read low.

Mine came up after a couple rides and it reads 145 in both holes on a china compression tester.
 

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I wouldn't have even checked the compression until the rings were seated.

Like said above, it should creep up some more. If your concerned, try a different gauge. They all read a bit different.
 

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I agree. Let the piston's take a seat and I'm pretty sure your compression will come up. I installed the SPI dual ring kit and I'm getting 150 psi cold. I'm worried for the opposite reason. Set my gap as you did and had the cylinders deglazed. Both reading 145 hot.

Let it snow.
 

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Discussion Starter · #8 ·
Thanks guys... I'll run it for a while and get it broken in good before I worry any further.

MBrett - sounds like those dual rings seal up real tight - I would say as long as you had checked clearances in cylinder and end gap, you should be fine. Was a little nervous about going to the dual ring pistons on the 600HO since they haven't been tried/tested long in real world riding on the 600HO's. Maybe next build I'll give em a shot. Let us know how it goes this season with them.

Now we just need some snow!

- BlyDoo
 

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Thanks guys... I'll run it for a while and get it broken in good before I worry any further.

MBrett - sounds like those dual rings seal up real tight - I would say as long as you had checked clearances in cylinder and end gap, you should be fine. Was a little nervous about going to the dual ring pistons on the 600HO since they haven't been tried/tested long in real world riding on the 600HO's. Maybe next build I'll give em a shot. Let us know how it goes this season with them.

Now we just need some snow!

- BlyDoo
I hope so. I was very meticulous during the rebuild. The guy that did my cylinders is one of the best in the area and only charged me $ 15.00 to deglaze both. She sounds good, can't wait to get some riding in. I'll post as soon as I have so good info.

Let it snow!
 

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DOUBLE CHECK TO MAKE SURE YOUR RINGS ARE INSTALLED CORRECT. A MARK, THE WORD TOP, SHOULD BE TOWARDS THE PISTON CROWN. CONCAVE SIDE UP. SEE IF THIS HELPS YOUR COMPRESSION. ALSO CHECK THE THICKNESS OF YOUR BASE GASKET. THIS WILL PLAY WITH YOUR COMPRESSION READINGS. SEE IF ALL THIS WILL HELP YOU OUT.
 
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