Compression Questions

[impulsive]

Hi,

Excuse me while as i post for my first time and i am unsure if it has been covered already. I do note the previous post but it is retrospect to a different engine.

I just completed a compression test on my 2005 seadoo gti le rfi.

Cylinder 1 - nearest to the front came in consistently at 140 psi.
Cylinder 2 - Came in at 120 psi

I would like to know the factory psi rating, however cannot find it anywhere in the online manuals nor can i find an acceptable level before rebuild is required. Is it rebuild time, do i sell up, or do i run with it

 

[El Toro 33809]

Welcome to the forum. The compression on this motor should be about 150 I believe. Above 135 would be okay for a while. You have two related issues here. First, the one cylinder is low at 120. Second, the difference in compression between the 2 cylinders should not be more than 10%.

The top end needs some attention.

 

[impulsive]

assuming the compression is low, the piston rings, valves, and head gasket would be in question correct?

 

[El Toro 33809]

This being a 2-stroke, there are not valves like you have in 4-cycle engines. The low compression would be due to ring, piston and cylinder wear.

 

[impulsive]

This being a 2-stroke, there are not valves like you have in 4-cycle engines. The low compression would be due to ring, piston and cylinder wear.

is that usually what causes it, worn rings? I could only imagine its not an overly hard excercise to refit rings etc if needed. however im assuming its def a motor out job.

$1800 i got qouted the other day for a top end rebuild. Can get the parts online for $200 at my door..

 

[El Toro 33809]

No way go with the $1800 quote. You could probably fly one of us over to do the work for you for that price!!!

It should be relatively easy for you to do yourself. It may just need rings, but you should measure the cylinder after you take it apart to determine the proper course to take. Good luck mate!

 

[impulsive]

thanks a lot for your help, i am going to a wet comp test tomorrow.. and take it for a run to see how its behaving, if its running well then i will probably keep it as is.. If not i will attempt to fix it.

I can only imagine the most damage that can occur is a little less power, and worn plugs all the time. would that be fair to say?

 

[LouDoo]

It sounds like it's time for at least a top end rebuild. Do you know how many hours are on the ski?

Ordinarily it's usually cheaper just to get a rebuilt engine, however I know that you are in Oz and rebuilds can be expensive. Try posting on one or more of the Aussie threads in the Regional Section of this forum and see what the locals say.

Lou

 

[impulsive]

yeah, i got qouted $1800 for a top end rebuild.. ridiculous i reckon. Just reading up now on the engine removal.

 

[impulsive]

yeah, i got qouted $1800 for a top end rebuild.. ridiculous i reckon. Just reading up now on the engine removal.

Forgot to ask, is it possible to replace the rings from inside in hull, basically without removing the engine.

Also if i have to remove the engine, is it essential to use an alignment tool? should replacing the shims etc be enough?

 

[LouDoo]

Yes, you can do a top end rebuild without removing the engine. Normally when you remove the engine you should use an alignment to to re-install, however on this new of a ski you might get by with just replacing the shims in the same place.

Here's another option that you might want to consider, you send these guys your cylinders, they will bore them fit new pistons, rings, etc. and provide you with all gaskets. Since the weight is a lot less it might be feasible freight wise. Personally I have not used them but a friend of mine has and it worked out great.

http://www.fullboreonline.com/sea_doo_720_top_end_rebuild_kits.htm

Lou

 

[Spimothy Leary]

I might get flamed for posting this, but oh well.
since one of your options was to sell it... and I rarely suggest selling a ski thats not 100% but lets face facts, its done all the time, sometimes because the seller has no idea whats wrong.
so with that said:
If your considering a sale, now is the time, especially if it run's well enough on the water, you can't always tell that its low on comp while riding unless your really in "tune" with your ski, and theoretically it could run for quite some time like this.
not saying to hide the issue, but I am saying that 80%-90% of your potential buyers will not bring a comp tester with them. I've sold more than a dozen ski's in the past 18 months alone, all with perfect compression, and I've had Zero Buyers do a comp test, Zero, and i've only had two buyers insist on a test ride a vast majority of the time the buyer will just want to start it on the trailer, see that it idles and make sure the gauges work and the hull isn't all beat up.

I've even had 3-4 sales where the buyer didn't even take more than a cursory glance at the inside of the hull, (they don't know what they're looking for: so to act cool, they don't look hard for anything), even after I've spent significant amounts of time cleaning and scrubbing the hull, painting the engine, replacing fuel lines & filters, etc, they lift the seat, glance around, and put it back quickly
(its a little disappointing sometimes since I feel that my efforts were unappreciated)

So just for the sake of discussion: this could be sold as a running ski, and you could move on to another model.

 

[impulsive]

well the ski runs great on water, maxing at around 83KPH today which is about right. Out of water it is a little more smokey, but starts and runs well.

I also spoke to a few mechanics around here and they said as long as the ski is giving you no trouble there is no real cause for concern. So all is good.

As for selling, that was my thought on the way home.. Sell it as an average, but running jet ski. But i think i will keep it, as i only paid $4000 for it in 2007 anyway. Unsure at the moment.

Can anyone tell me any other likely problems to look for? Is anything else a common issue other then top end rebuilds?