Just placed a fix kit on my sled, new pistons, rings, gaskets ect. Cylinders looked great, no issues with any parts. I ran a few heat cycles and have put 70 miles total on the sled sense the rebuild, runs fine no complaints. I had the hood off to clean up the belly pan and ran a compression test for the heck of it. Sled was cold, throttle was held wide open and I only got 100 psi in each cylinder. I tested another pro with the same gaugee/process 125 psi was the reading which is normal. I've had a few buddies tell me rings can take awhile to seat. Has anyone had this experience or heard of it? Any sugestions?
Low Compression
- Thread starter Riches336
- Start date
What fix kit did you install
I used CPI, with SPI pistons.
I used CPI's with SPI pistons
I
inspector01
Well-known member
What was ring gap?
The supplied rings "SPI" I beleive, standard gap. They were much tighter than the OEM pistons that came out with 1600 miles.
There isn't a "standard" ring gap. you put the piston ring in the bore squarely by itself and measure with a feeler gauge the gap between the ends of the rings.
Yes, rings do take some time to get seated and it takes even longer if your running synthetic oil. 70 miles isn't near enough regardless of the oil being used. "heat cycles" is a BAD idea on new pistons and rings. You need the cylinder pressure under load to force the rings out into the cylinders to get a good seat. when its just idling all you are doing is polishing the rings and making it harder for them to ever get a good seal with the cylinder.
Eric
Yes, rings do take some time to get seated and it takes even longer if your running synthetic oil. 70 miles isn't near enough regardless of the oil being used. "heat cycles" is a BAD idea on new pistons and rings. You need the cylinder pressure under load to force the rings out into the cylinders to get a good seat. when its just idling all you are doing is polishing the rings and making it harder for them to ever get a good seal with the cylinder.
Eric
Depends on the piston type and bore/cylinder clearance. I do agree that the sooner you can load the rings the sooner they will start seating. However, sometimes it is required to let the pistons run for a while first. Running an extra tank of fuel for break-in is better than scuffing or seizing a piston if it is required.
I don't know how the SPI pistons compare to the stock pistons on that model but on the 700 the deck height is shorter. If that's the case here, it would lower your compression from stock and also raise the port timing some.
I recently built a 660 and had a OEM piston and a SPI piston here to measure with. I cant remember off the top of my head what the measurements were, but the SPI was substantially shorter.
I recently built a 660 and had a OEM piston and a SPI piston here to measure with. I cant remember off the top of my head what the measurements were, but the SPI was substantially shorter.
Update on the low compression. I went to Pinedale WY over the weeken, sled now has over 100 miles on fresh topend. There were several long pulls and I actually rode the sled rather than trying to break it in. The sled ran okay, wasn't pulling the RPM range I'd like 77-7800 which could be clutching on some of the steep hills. Just wasn't super impressed for a sled with Carls clutching, full SLP system and a power comander. Came home tested the compression today and still 100PSI! Kinda frustrated as to pull the motor back down and see about different pistons or if there is just something going on with the exhaust valve decompresion ports? I just have a hard time thinking it's the motor with it being so fresh. I am running synthetic oil just "Polaris VES racing", I turned my oil pump up, premix my tank with a little oil and I run ethenol treatment... I worried the entire day if my sled went down were we were at I'd never get it out. A sled with 100 PSI doesn't seem like oll reliable to me. Any sugestions would be awesome.
Justin
Justin
X
xc6rider
Well-known member
Did you have the cylinders honed or deglazed? Didnt think i saw it mentioned...
pull it down to see if anything looks off. get cylinder deglazed, and slap her back together with new rings if ya dont see anything.
Or, run it a few more days and see if it seats in, which, i doubt it will at this point.
Double check ring orientation and gap also.
pull it down to see if anything looks off. get cylinder deglazed, and slap her back together with new rings if ya dont see anything.
Or, run it a few more days and see if it seats in, which, i doubt it will at this point.
Double check ring orientation and gap also.
