Low compression: rebuild now or take the chance??

[Redneck_indy]

I have a 2015 indy 600 with 8800 miles on it. I did a compression test on it just for kicks and giggles. On the mag side I had 125psi and on the clutch side i had 100-105 psi. I've always heard you want to be within 10% of each other. The sled is running great tho. I'm supposed to be in Houghton Friday morning. Do I cancel my trip/rent a sled or should I ignore it for now since it's running great and refresh the top end at the end of season if I make it that far lol. Your thoughts??

 

[garageguy]

Run it its middle of Feb. Allready

 

[snake]

run it,wouldn't hurt to try some "ring free" in fuel and test again after the trip.....might get lucky with it being just a carboned up ring

 

[old abe]

A very good Poo dealer stated to my good friend, on a Liberty 800, compression at 110, do not hesitate, take it down, and REBUILD!!! 600???

 

[indy_500]

A very good Poo dealer stated to my good friend, on a Liberty 800, compression at 110, do not hesitate, take it down, and REBUILD!!! 600???

Gauges vary.... A LOT! With MY GAUGE I’ve never owned and/or checked a sled that has more than 115 psi. And the gauge has been used on at least 15 sleds. More CCs doesn’t mean more compression. In fact all of the 600s I’ve owned have generally been between 110-120 with my gauge, and both of my 800s have never been over 110. My 15 Indy 600 at 9000 miles with my gauge had 105 psi on each side. After I tossed fresh pistons in I’m now at 110. To answer the original posters question, I would be slightly concerned that you’re 20 psi off from one side to the next. That’s kind of a lot. I wouldn’t feel that warm or fuzzy if it was anything more than 5 psi different side to side. BUT, if you’re looking to run it for 1 more trip and calling it a year afterwards, I personally would chance and give it a go. But I don’t think it has an entire month of riding left in it, but you never know.

 

[old abe]

A good friend just recently bought a super clean, well cared 2015 Liberty 800 sled. He didn't ask on the Poo 600, however Poo dealers say "Liberty 800" should run out at 120-130psi. Around 140 brand new. When at 110 psi replace pistons/rings, and check cylinder bore to avoid big problems. Keep close check after 4K, 4.5K miles is a good idea. I wood reason the 600 should compare very close on compression psi. My Doo's run at 130 psi+.

 

[Cirrus]

Very interesting thread....I had the same questions/concerns when I bought a demo 800 for the wife, so I got my hands on a full test kit from A&E Tools, with all the attachments. (My place of employment)
I talked to quality control and the engineers about the accuracy of the gauges, and how to test.
First of all, you need to test COLD, not warm, to get the best base line reading.
With a brand new gauge, on a cold test, at 700 miles, the sled was reading 116-118 consistently. Test it hot, you will get higher readings.
Oh - and the other thing you want, is both cylinders to be within 1-2 PSI of each other.

 

[old abe]

Very interesting thread....I had the same questions/concerns when I bought a demo 800 for the wife, so I got my hands on a full test kit from A&E Tools, with all the attachments. (My place of employment)
I talked to quality control and the engineers about the accuracy of the gauges, and how to test.
First of all, you need to test COLD, not warm, to get the best base line reading.
With a brand new gauge, on a cold test, at 700 miles, the sled was reading 116-118 consistently. Test it hot, you will get higher readings.
Oh - and the other thing you want, is both cylinders to be within 1-2 PSI of each other.

Agree

 

[timo]

my 2 cents is to rent one.
Being 20-25 psi difference is big and on top of having 9000 miles on it. Maybe do another compression test to confirm.
I know I wouldn't want to go to the UP with a group of guys knowing i could be riding a time bomb and ruin their weekend when it blows. also if I had a guy in our group go riding with us and he knew he had this issue and came anyway and it blows i'd be a little upset.
Now if your riding local it's not that big a deal.

 

[fish633]

The procedure for testing compression is often done improperly resulting in incorrect readings.
With the engine cold hold the throttle wide open and crank until gauge pressure stops rising,thats your #.
if the crown of the piston has a build up of carbon that will affect the outcome as well.
20 psi difference is not a big deal if both cylinders are within normal operating range
Have you pulled the head and checked out the cylinder for scoring or plating wear?
9k without a top end thats getting a bit sketchy

 

[Redneck_indy]

Well after 9k miles the sled is in rough shape lol. Made it through most of the weekend. It still runs but misses like crazy and been running on one cylinder half the time. Kills everytime I land a jump. Time for the rebuild, any suggestions on what kit to buy? How about forged pistons vs cast?

 

[indy_500]

Well after 9k miles the sled is in rough shape lol. Made it through most of the weekend. It still runs but misses like crazy and been running on one cylinder half the time. Kills everytime I land a jump. Time for the rebuild, any suggestions on what kit to buy? How about forged pistons vs cast?

I’m a big believer in cast pistons only in sleds. Forged struggle with temperature swings and require perfect warmup procedure, too many what-ifs for me in a liquid cooled machine operated in below freezing temps relying on snow to keep it cool... I just put SPI’s (now re-branded as SP1, same thing just changed from an I to a 1) in my 15 Indy 600 at 9500 miles, just rolled over 10k today and is running awesome. I have the axys 800ho SPIs with the oil grooves in my 16 pro rmk 800 as well, 500 mountain miles later it’s still running great also. I have installed SPIs in close to a dozen sleds and to my knowledge none of them have gone down since. Over 2k miles on my 04 pro x that I just sold to a buddy since I put SPIs in that sled. As you can see I’m a fan of the low cost SPIs. The cost savings alone would be my deciding factor in a 9000 mile sled. Chances are it needs a lot of other wear items replaced that will likely fail before a set of SPI pistons would.

 

[Redneck_indy]

Pulled it apart and found a chunk of the piston broken off and smashed it into the head. Head is shot along with cylinder and obviously piston and rings. Just gotta decide if it's worth rebuilding or just trying to find a new motor. Or even rebuild at all cuz I was thinking of pre ordering a sled next spring and looking to go a longer tracked sled. So not sure what I'm gonna do yet

 

[old abe]

Pulled it apart and found a chunk of the piston broken off and smashed it into the head. Head is shot along with cylinder and obviously piston and rings. Just gotta decide if it's worth rebuilding or just trying to find a new motor. Or even rebuild at all cuz I was thinking of pre ordering a sled next spring and looking to go a longer tracked sled. So not sure what I'm gonna do yet

The compression difference you stated in your first post indicated a real possibility of piston/ring problems that had already occurred. I absolutely agree with indy, nothing wrong in using SPI 1 pistons. I agree with him on "cast" vs "forged". Good luck with what ever you do!

 

[ezra]

Pulled it apart and found a chunk of the piston broken off and smashed it into the head. Head is shot along with cylinder and obviously piston and rings. Just gotta decide if it's worth rebuilding or just trying to find a new motor. Or even rebuild at all cuz I was thinking of pre ordering a sled next spring and looking to go a longer tracked sled. So not sure what I'm gonna do yet

It is a 15 you got to rebuild . Not that much even if you need a new jug and head some spi slugs and let her buck
If you hurry you can get still get her sold so you have a few extra bucks to snow check or get in on the almost no use spring deals