96 Speedster Compression Question

[Cheap Engineer]

I've been chasing a problem on a '96 Speedster and I just did a compression check and I think I found the problem. On my port engine the mag cylinder is reading 150 while the PTO is reading 120. I've done the test a couple of times now and it comes out the same. Could this cause the engine to run rough and not be able to make full power? I rebuilt the carbs and the engine starts right up, but has trouble making power in the water. If I turn right and get the prop out of the water the engine rpm's come right up.

If the compression is a problem it looks like new piston rings are in order. I've done the carbs and wear rings on the boat. How hard is it to do the piston rings? Any special tools needed? Anything else I should replace while I'm in there?

Thanks,
Carl

 

[HodgesZ28]

I've been chasing a problem on a '96 Speedster and I just did a compression check and I think I found the problem. On my port engine the mag cylinder is reading 150 while the PTO is reading 120. I've done the test a couple of times now and it comes out the same. Could this cause the engine to run rough and not be able to make full power? I rebuilt the carbs and the engine starts right up, but has trouble making power in the water. If I turn right and get the prop out of the water the engine rpm's come right up.

If the compression is a problem it looks like new piston rings are in order. I've done the carbs and wear rings on the boat. How hard is it to do the piston rings? Any special tools needed? Anything else I should replace while I'm in there?

Thanks,
Carl

If your going to do rings you might aswell refresh the entire upper end. It could save you in the long run.

 

[kustomkarl]

Actually, the correct procedure is to use a Micrometer and check the clearance of the cylinder sleeve and piston to determine if the piston/ sleeve needs to be replaced or honed/ bored out. No sense just replacing the top end if you only need new rings and gaskets. Check out the top end by the specs in the manual and go from there.

Karl

 

[seadoo GTS 1993]

Hey man, I live rite by u... is that the green and purple speedster? Do you live by like 17 and hayes?

 

[Cheap Engineer]

I'll check the pistons and cylinders against the manual while I'm in there. I still wonder if the compression requires new rings. I read that Seadoo engines with compression that is more than 5% different should be reworked. Is that right? I'm at 17%.

Seadoo GTS 1993, I live a little further up the street at 21 & Hayes with a yellow and white speedster.

Carl

 

[kustomkarl]

Rule of thumb is 10% difference is about the correct difference allowed. I bet you could just re-ring it with a quick light hone on the cylinders should do it. It's not a race boat...so the budget should be an important factor.

Karl

 

[seadoo GTS 1993]

Oh ok.. different speedster im thinkin of then... and yea like karl said.. 10% difference is rule of thumb

 

[Chester]

I've been chasing a problem on a '96 Speedster and I just did a compression check and I think I found the problem. On my port engine the mag cylinder is reading 150 while the PTO is reading 120. I've done the test a couple of times now and it comes out the same. Could this cause the engine to run rough and not be able to make full power? I rebuilt the carbs and the engine starts right up, but has trouble making power in the water. If I turn right and get the prop out of the water the engine rpm's come right up.

If the compression is a problem it looks like new piston rings are in order. I've done the carbs and wear rings on the boat. How hard is it to do the piston rings? Any special tools needed? Anything else I should replace while I'm in there?

Thanks,
Carl

Take the head off and look inside. A compression test is not an accurate indicator of piston and cylinder wall condition. You can have a piston seizure and still show good compression. With only 120 psi you will see some damage to the cylinder walls. Post a picture of it. I'm sure you will need more than just rings.

Chester

 

[Cheap Engineer]

Okay pulled the head and here is what I found. Mag is on the left, PTO is on the right. From what I can figure it looks like part of the ring got loose and gouge up the head a little bit. I didn't have time to pull the cylinders, that is tomorrows task. The PTO cylinder had 120psi in the last check. At least I think I found the problem. Thanks for all the help so far.

Carl