Score!!!!!!! Looky what I got!

[spx787]

Yea wide open throttle

 

[AdamXP800]

No warm up on that reading. My gauge reads 5-10 psi low always



96 XP800!
Keep the 2 strokes alive!

 

[spx787]

O

Yep, 120psi is low for an 787 but have you started and run it yet? Someone said their brand new reman from SES was only blowing 120psi and TOM told them that's the pressure he expected.

I guess what I'm saying is if it's been rebuilt the rebuilder may have detuned it slightly.

One thing that comes to mind is supposedly they become hard to start in the water if compression is too low.

Yes the engine will start up and run.

 

[Sportster-2001-951C-Stock]

I measured my 951 both ways (hot and cold), because everyone wants a cold compressions test for some reason... WUWT? Anyway, result was it blew the same pressure (122psi).

This "hot" test was immediately after running 3 minutes while in the water at 3000~3500 RPM

 

[Sportster-2001-951C-Stock]

O

Yes the engine will start up and run.

Thing is, if there's too much combustion gas blow-by due to worn rings, piston, or cylinder wear the oil film between the cylinder wall and piston can fail and cause seizures, often this starts with partial seizures where bits of molten aluminum slough off the piston and stick onto the iron cylinder wall.

 

[AdamXP800]

O

Yes the engine will start up and run.

Running on land and running in water with a load is 2 entirely opposite scenarios



96 XP800!
Keep the 2 strokes alive!

 

[spx787]

It's rare to have both cylinders drop evenly in compression. If they are both dead on 120 your probably ok.
Did you do fuel off throttle wide open when testing?



96 XP800!
Keep the 2 strokes alive!

Hoping you're right. The engine runs well out of water but I won't be able to tell anything till I get it in a ski and out on the water for the ultimate test. Since you can rebuild the top with the engine in the ski, I may just wait and see how it does. Of course, this is all off in the future. I don't even have a hull yet.

Is there some sort of plate or something I can remove to take a look at the bottom end? I just want to make sure there is no silt or debris in there.

 

[Davidgsx]

Dude!! Way easier to to a top end with motor on bench!!


Sent from my iPhone using Tapatalk

 

[spx787]

Dude!! Way easier to to a top end with motor on bench!!


Sent from my iPhone using Tapatalk

Ok then. I'll just go ahead and do it then. Where is the best place to buy a top end rebuild kit?

 

[Spimothy Leary]

i'm a fan of full bore, their prices are about the same as SBT's dealer rate and I think they do better work. Send them in, they return originals, I assume turn around would be pretty reasonable this time of year. FB's prices are very similar to what you would spend buying a piston kit and having a shop do your bore, same price, less effort.

 

[spx787]

But the whole thing is, others have said in this thread that some reman engines are only doing 120psi. Both cylinders were pretty much DEAD ON 120 both times I ran the test. From what some are saying, that usually points to the guage being off. If I understand correctly, normally if the top end is bad you'll have one cylinder reading significantly lower than the other. That's why I was saying that maybe I'll just try it out before spending $300 to rebuild the top.

I don't have another gauge as this one was a loaner from Vatozone. I guess I could take it back and ask if they have a different one I can use to make sure.

 

[Sportster-2001-951C-Stock]

If you don't know whether or not the gauge is accurate, just compare the reading with your other 787's and motors, seems obvious. If they all blow low probably the gauge is out of calibration. Then, find an air source such as your air compressor with a gauge on it (most have gauges, right?) for a quick comparison.

If you're gonna run 2-strokers or even marine engines you have to monitor their health so a compression gauge is mandatory, Harbor Freight sells some that are adequate.

 

[Sportster-2001-951C-Stock]

Any idea of how many hours are on this ski? Not that low hours means it's not worn out but high hours can mean it's got wear.

If the hone marks are still in the cylinders it's got to be pretty fresh, thus if hone marks are mostly there I'd conclude it's probably been rebuilt. Also look for other signs it's been rebuilt, might have a warranty tag on it or overheat pills attached, there should be some clues. The oversize pistons will have the new bore size on their crowns, if the number is larger than factory bore there's that could be why (head work, or thick cylinder base gasket).

Just trying to help you figure it out, not make you toss a bunch of hard-earned cash into the motor if/when it's unnecessary.

 

[Sportster-2001-951C-Stock]

i'm a fan of full bore, their prices are about the same as SBT's dealer rate and I think they do better work. Send them in, they return originals, I assume turn around would be pretty reasonable this time of year. FB's prices are very similar to what you would spend buying a piston kit and having a shop do your bore, same price, less effort.

I tend to agree with this, FB does good work with the RV motors from what I've read about.

Not sure if they chamfer the cylinder ports or leave it up to the buyer but at least look it over before assembly b/c you don't want a ring to snag in the ports.

 

[CReynoldsMIZ]

Yep, 120psi is low for an 787 but have you started and run it yet? Someone said their brand new reman from SES was only blowing 120psi and TOM told them that's the pressure he expected.

I guess what I'm saying is if it's been rebuilt the rebuilder may have detuned it slightly.

One thing that comes to mind is supposedly they become hard to start in the water if compression is too low.

That was me. Tom said they come from his shop blowing 140 psi and that is the compression they came from the factory with. His words not mine

 

[Brian J]

A top end might be easy to do but how much does it cost? (honest question, I don't' know).

Let's remember this thing was in a flood, before you dump money into an engine that will still have the old 'been in a flood' bottom end can you put it all together into a hull and test drive it? Earlier posts made it sound like you're getting a hull for free.

If it was me I'd ride the thing until it lets go and then buy a reman motor. Or before you get too deep into this project, how much does a water ready SPX with good compression cost in Texas in November..... I know that goes against what this thread is all about but it's something to think about.

 

[Sportster-2001-951C-Stock]

That was me. Tom said they come from his shop blowing 140 psi and that is the compression they came from the factory with. His words not mine

Okay thanks, I wasn't sure exactly the details, memory not so good anymore.

The pressure they blow not only depends on ring seal but the combustion chamber volume as well of course so the root cause needs to be determined b/c blow-by is the phenomenon that can cause the oil film to fail and low(er) compression is just one of the symptoms.

We can see the above pic of Adams showing 145psi on a healthy motor that is most likely broken in properly and has hours on it, seems to be ~145 psi in his case.

 

[spx787]

Basically, I am looking to build a ski and come in at a cost considerably lower than buying one outright. I got this thing for $250. I got a lead on a hull right now that I could get for $50 or less that still has everything except the engine and electronics in it.

4 months ago, I paid $1300 for my SPX and a POS homemade trailer. I'm trying to come in at $800 or under by the time I'm done with this project. I do realize that I may end up spending more but I enjoy working on things (I am an aircraft mechanic but now I teach the trade). There's something to be said and a sense of satisfaction when you do things like this yourself. The whole "built not bought" mentality that goes along with a project like this.

 

[Sportster-2001-951C-Stock]

Yep, I guess it's your call on whether or not to rebuild the top end. Could be the crankcase has silt in it and if that's the case the crank bearings will be contaminated and the crank will need to be replaced.

If it was a 951 I'd be leery of tossing a connecting rod through the block and destroying the case, this is one of my fears for my motor but so far it's hanging in there.

All 2-strokes are destined to seize eventually and ideally should be rebuilt before that day arrives.

 

[soccerdad]

I would put the motor on your bench and remove the RV cover. Then look in there at the crank as good as you can. Look for rust and/or silt. Also, dump out the oil from the RV gear case section. Does it look like it has water in it? You can also put some solvent/gas, etc into the lower end through the RV opening. (fire extinguisher handy )spin the motor over by hand a few times with the plugs out. Then turn the motor upside down and pour it back out. Look at what comes out. Should just be solvent and oil. That should give you the warm fuzzy on the silt issue.

Then just compare the gauge reading on this motor to your good other ski and that will tell you the rest of the story. That takes the gauge out of the equation quickly.

 

[spx787]

I just had a guy contact me from my craigslist ad with a 96 GTX with a blown motor. Awaiting pics. He told me it's been sitting for years and is sun faded. He thinks his son put the wrong oil in it. It started knocking really bad and then died and has been sitting since. It is a complete ski though and shouldn't require much more than a motor swap.

Also have a guy with a 96 XP hull but his is empty and he is gonna be an 8 hour round trip to go pick it up.
[MENTION=69521]soccerdad[/MENTION] Yeah, I'll probably start pulling the motor this weekend and will definitely try the things you suggested.

 

[spx787]

Just got pics and it's actually a GSX.

 

[Sportster-2001-951C-Stock]

Is he throwing in a trailer to seal the deal?

 

[spx787]

It's a double trailer with another ski on it so I don't think he's throwing that in lol

 

[soccerdad]

A 96 GSX is a great ski! Lou will back me on this. Don't ask David, he tried to get rid of his... But we talked him out of it. But seriously, the GSX would be great. Just swap motors and you will have almost a full spare ski worth of parts. Is the GSX a good price?