Thread: Very LOW compression RX DI
09-09-2010, 08:37 AM #1
- Join Date
- Jul 2010
- Rock Hill, SC
Very LOW compression RX DI
I have good buddy of mine who was riding (RX DI 951) with me this past Monday and had a bad failure. He is not exactly sure what happened but I will list what happened below.
1.Had trouble cranking ski after we ate lunch. He had to crank it a few time to get it to run. Once the ski started it ran great and was hitting full speed just like normal. (we had about a 45 min. ride to lunch and then had the skis shut off for about an hour while eating)
2.After ridding for about an hour down the lake he shut his ski off in a no wake zone a for few min. to take a break. When he tried to restart his ski it would spin over fine but would not crank. It would fire for a very brief second every once in a while but never ran.
After we towed it back to his house the next day he did a compression check after looking over the usual plugs and what not. The front cylinder read 70 PSI and rear cylinder read 15 PSI. It seems very weird that he would have burned up a motor being it was running great up until he shut off the motor. Is there something else that could be wrong? What all can cause the 951 DI motors to lose compression. My buddy is thinking it may be possibly something to do with the air pump for th RAVE valve system but I do not see how that would affect compression so much.
I am not exactly sure all the specs on the ski but I will list below some more info.
1.year of ski – I think it is an 04. I know it is a red RX DI with the 951 motor.
2.I think it has between 130-150 hours.
3.I know for a fact he ALWAYS runs the correct Sea-Doo synthetic oil and has owned the ski since it was new so it has never had the incorrect oil used. Always the correct Sea-Doo synthetic oil.
4.I think I remember one of the plugs being a little wet when pulled them out on the lake.
I will admit one thing that maybe he should not have done was about 6 weeks ago we were at the beach ridding and he put some 87 octane gas in the ski at a marina because he was out of gas and needed some to get back to the ramp. After pulling the ski out of the water then filled up with fresh 93 octane gas. I do not think he had much 87 octane in his tank but can low octane gas mess up a DI 951 motor??? This 87/93 octane mixture was still in his tank when we ridding the other day when his motor messed up but it should have been mostly 93. I am sure people who live on lakes fill up those Sea-Doo RX DI skis all the time at marinas with 87 octane???
What seems really weird is that both cylinders are so low on compression. As I stated earlier the front cylinder was 70 PSI and the rear was 15 PSI. The weird thing was the ski ran great until he turned it off. How could an engine with that low of compression just be running fine one moment and then after cutting it off for a few min not even start due to loss of compression? What all can cause loss of compression?
09-09-2010, 10:31 AM #2
- Join Date
- May 2010
- Savannah, GA
I am sure you will get the help you are looking for. But here is what I can tell you. I blow both my skis motors this summer. Both ran the best just before it let go. Think I got about 200 more RPM out of it before she went on my Seadoo.
As for the fuel lower octane does not burn as hot so lower would not caused any problems. At least I do not see how. Most motors that need the higher octane requires a hotter fire there for you get more hosepower and runs cleaner.
good luck and check your bottom end you may only need to redo the top end save some money.
09-09-2010, 11:18 AM #3
- Join Date
- Nov 2007
nine out of ten times it will be seized pistons and stuck rings, it wont start because of low compression ,when engine is running high rpm it still makes some horsepower as there is not time for all compression to blow by piston and rings, if he could get it started it might run ,but chances are youll need some oversize pistons and a bore job.hopefully your crank is ok but i would really make sure it is clean before doing top end, i just rebuilt a 951 with wisecos and it runs awsome!!>Marvin
09-09-2010, 07:33 PM #4
If it's red it's an 03. In 2004 the 4 stroke RXP replaced the RX.
09-10-2010, 12:50 PM #5
01 DI is the only year where high octane fuel is required. I guess you can look on the bright side. You didn't end up with a huge hole in the side of the cases somewhere.
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