rotaxrule1
Well-Known Member
Hi folks,
I've been doing a top end rebuild on my 2001 RX DI over the winter, I am completely baffled at this point. If any of you DI experts out there can chime in, I would be so thankful. Let me try to explain as briefly as I can.
Thanks in advance, sorry for the long story.
I've been doing a top end rebuild on my 2001 RX DI over the winter, I am completely baffled at this point. If any of you DI experts out there can chime in, I would be so thankful. Let me try to explain as briefly as I can.
- Ski has about 100 hours on it, it looks new and has run like a race ski over the past 2 years that I have had it EXCEPT the occasional hard start when warm (didn't think anything of it at the time, now I know I should have taken that as a warning sign...)
- Last fall on our last ride out, it was occasionally sputtering and cutting out. My nephew warned me, but I said to keep riding it as I assumed it just had some bad fuel or would "clean itself out"
After a while of riding around, they brought it back and it wouldn't start back up after shutting off. - Compression tests showed 110 on PTO cylinder and 60 on the mag cylinder, bingo.
- Pulled top end apart
- Mag cylinder had massive signs of detonation and had a missing chunk about a half quarter size along the crown.
- PTO side was intact but also showed signs of light detonation and obvious lean burn (piston also was considered damaged since it was pitted on the dome)
- Both cylinders are scored pretty badly, more so with the mag side.
- I inspected the lower end the best I could and got it cleaned out. Given the lower hours on the ski, I decided to go with a top end rebuild (I obviously accept the risk if it grenades on the lower end, I got this thing for $1300 so
) - While I have it apart, and given the symptoms it had before the meltdown, I thought it would be crazy not to rebuild the air compressor, so I bought the SBT rebuild kit and put the new sleeve, seals, piston rings in. (the compressor condition was surprisingly flawless, no signs of failure but nonetheless...) I learned that I couldn't replace the whole thing without pulling the motor and rear balancer out, which may as well be a full engine overhaul at that point, so I stopped there.
- Given the condition of the cylinders, I had to have it bored out to 89.4MM via my local powersports shop (matched up to wiseco oversize) Had rave valves cut to match.
- Bought a SBT full gasket kit, I assume it comes with a 5 hole base gasket.
- Installed everything, and this is where it gets interesting.
- Recommended "CC test" from shop manual indicates 43CC liquid capacity in each cylinder, spec is 44.5-46CC, which I interpret as too high of compression
- I then did the easier to interpret "squish test" and originally saw about 2.55MM using the 5 hole base gasket
- To confirm I am not measuring something wrong, I put the fuel rail on and performed a compression test, 90PSI exactly on both cylinders (way low)
- Thinking I had a base gasket that is too thick, I bought a 3 hole 951 gasket and installed it and performed my tests again
- Skipped CC test this time, performed squish test and got about 2.3MM (reduced but not substantial)
- Compression test: 95PSI exactly on each cylinder
- Though the service manual doesn't specify, and the CC test sort of contradicts my findings, I have seen the squish gap range needing to be about half of what I am seeing, which would correlate to my low compression readings (I'd expect about 120+ at my altitude of 4300 ft, which is what it had before the meltdown)
- Thinking it must be the wiseco pistons, I took them back to the shop that did the cylinder work and had them take measurements of the original pistons and the wiseco pistons, compression height and all specs are identical, so I guess a "wrong piston" is ruled out, or is it? ShopSBT indicates a different part number for the carb 951 vs DI pistons, is it just because of the protective coating on the DI pistons? Are they sized different at all?
Thanks in advance, sorry for the long story.
