HELP !! Compression test question

[Riixxii]

Re: HELP !! Compression test question

If genuine Rotax rings were used in the rebuild it will take longer to seal to the bore. Most rings have a teflon coating on the outer edge of the ring that permits quick sealing to the bore. The hard chrome face of the top ring requires more time to seal to the bore. That could be your extra 30lbs of compression.

[Bill O'Neal2]

Re: HELP !! Compression test question

More than likely, it is the guage he was using or the battery was charged more..

[Technical Support]

Re: HELP !! Compression test question

The break-in time of the engine and/or brand/type of the rings has nothing to do with a 50 lbs. low reading, period.

[Riixxii]

Re: HELP !! Compression test question

You might want to do a little research on the "nothing to do with it period" if you're the so called professional. I've compression tested all of your SBT engines before the initial water test and also when they come back for 20 hour checks. There is a difference after they've been run for a while. Or is there not? And furthermore a 130lb. reading is well in the range for a 6.1:1 compression ratio on the 951 Xp. I'll be testing the next 951 we get at the shop and if it doesn't have at least 150lbs. plus I'll be sending it back then.

[Technical Support]

Re: HELP !! Compression test question

I didn't say it doesn't change - I said a 50 lbs. difference.

[schultztec]

Re: HELP !! Compression test question

folks,

I cant buy the fact that it was a faulty guage because i used two different guages and got 100 psi with both guages, However the battery being charged more and the rings seating could be a possibility ?? Question, could the power valves effect compresion reading ???
Chris

[Riixxii]

Re: HELP !! Compression test question

The P.V.s would not effect the readings as the compression is determined at the top of the stroke. That is your "squish" Different base gasket thicknesses,milled head surface and/or different cc domes will vary the lbs of comp. Bill definately has a point on the battery issue though, if the ski sat for a while and you did the comp test, it wouldn't crank as good as with a fully charged battery. The last test you did resulted in 130psi. both cylinders is acceptable for that engine.

[Bill O'Neal2]

Re: HELP !! Compression test question

If the power valves are opened when you test the compression, you will see lower compression than if they are closed. Don't believe it? Hold one open or remove one and do the test.
The reason that the power valve effects the compression is that you will have more volume of air being compressed into the chamber when the power valve in closed.

[Riixxii]

Re: HELP !! Compression test question

I'll try it. Learn somethig new everyday.

[schultztec]

Re: HELP !! Compression test question

Thanks for the good info, I was still planning on a rebuild this winter because of what I have found to this point, who knows what else is messed up. UNLESS these are some performance tuning secrets that even Bill O and TS are not aware of, "you know the old non working PV's and unsynced carbs":emoticoni . But in reality I was planning on a coffmans pipe, rev limiter Novi carbs and a Miler head and I want to be sure I have a good top end to start with. I would think from what I have read this setup should still be fairly reliable..
Chris

[Bill O'Neal2]

Re: HELP !! Compression test question

I would only consider it a good price *IF* that is all of the money that you need to spend and that you end up with a very good running XP.

If there is more money to be spent to get it right, them pass on this ski. There are lots and lots of available used watercraft in America. Some at good prices, others not so good.

[Riixxii]

Re: HELP !! Compression test question

If you we're only lookin for a ski to "build" you shouldn't even be worried about the compression and plan on building it from square one the RIGHT way. There are a lot of sites to give you info on what components you need, hell, Bill can sell you the complete setup with some porting included for less than what it will cost you on the street. Right Bill? Hook him up and quit wasting our time on compression issues if you plan on having the ski tweaked out.

[98xlt]

Re: HELP !! Compression test question

OK, I had to ask. Did you get a trailer out of the deal too??

[schultztec]

Re: HELP !! Compression test question

sure did

chris