1994 Sea-Doo GTX rotary valve timing

[bevmale]

Looking for any help..Very much appreciated..I am totally stumped..Trying to maintain patience during my project.
For some reason, I can align rotary valve opening mark at 130 degrees, however, unable to align closing mark. Closest is 76 degrees I have tried turning valve..No luck..Followed correct procedure aligning 360 degrees on bottom of inlet for opening mark port and 360 degrees top of inlet port for closing mark..
Specs are:
OPENING 130 BTDC +-5
CLOSING 65 ATDC +-5

 

[POPPS]

Make sure your mag piston is at tdc. The valve is asymmetrical, so you can flip it over, and also that you have 5 degrees of variableness.

 

[bevmale]

Thank you..
Any source out there for a sea-doo p/n 295000065 TDC gauge?

 

[mikidymac]

Just buy a cheap dial indicator from Harbor Freight and drop it down the spark plug hole.

 

[POPPS]

Or, do what I have been doing for couple decades, put a 6 inch 3/8 extension into mag cylinder, remove your gray pto cover, and slowly rotate the pto/crank, till there is this small moment that the extension does not move, just slowly rock the crank back and forth, and bingo, you have tdc, since your valve timing has a variance of plus +/- 5 degrees anyway.

No problems doing this ever in 20 years.

 

[bevmale]

Totally stumped again..Appears the rotary plate on GTX has a 159 degree cut out angle..According to the manual, that is a XP valve..This motor has never been disassembled, repaired, etc..Obviously, this is the reason why I have been having issues trying to set timing at TDC...Any reason for this madness??.. Specs for this valve are:
OPENING 149 BTDC +-5
CLOSING 65 ATDC +-5

 

[AKnarrowback]

Was it the valve that came with the machine and has the machine run well before with the valve?

 

[AKnarrowback]

What type of motor is it? Meaning there is a black metal tag on the lower case next to the mag side cylinder, take a pictureof that tag. Also take a picture of the two carb holes in the rotary valve cover and a couple of the exhaust pipe. Send us those.

The reason I ask is that in 94 there were two versions on the 657 motor. Just want to confirm that, in the very remote chance, that machine did not get a motor swap at some point.

 

[bevmale]

Was it the valve that came with the machine and has the machine run well before with the valve?

Yes..Ran fine..

 

[bevmale]

What type of motor is it? Meaning there is a black metal tag on the lower case next to the mag side cylinder, take a pictureof that tag. Also take a picture of the two carb holes in the rotary valve cover and a couple of the exhaust pipe. Send us those.

The reason I ask is that in 94 there were two versions on the 657 motor. Just want to confirm that, in the very remote chance, that machine did not get a motor swap at some point.

 

[AKnarrowback]

Looks to be a regular 657, why the rotary valve is for a 657x is a mystery. I would look for the proper valve and put things back together according to specs.

What type of work have you been doing to the machine? Was there a motor failure?

The 94 XP had a 657x, 80 hp, motor. The 94 GTX had the 70 hp version of the 657. The 70 hp version was much smoother through the throttle range, the "x" version was a little more jerky at certain throttle transition points. If someone swapped to an "x" valve thinking they would gain more performance it was a waste of time, there were many other differences in the motors and their configurations.

I have both a 94 XP and 94 GTX. While more HP sounds like a good thing the factory calibration for the GTX was very spot on if the carbs and pump are in prime shape. It was a very user friendly machine with enough scoot to pull a double tube. Just 5 weeks ago I carried 4 full size adults on mine after my other gtx locked the pump up with a rock 10 miles from the boat launch.

 

[bevmale]

Looks to be a regular 657, why the rotary valve is for a 657x is a mystery. I would look for the proper valve and put things back together according to specs.

What type of work have you been doing to the machine? Was there a motor failure?

The 94 XP had a 657x, 80 hp, motor. The 94 GTX had the 70 hp version of the 657. The 70 hp version was much smoother through the throttle range, the "x" version was a little more jerky at certain throttle transition points. If someone swapped to an "x" valve thinking they would gain more performance it was a waste of time, there were many other differences in the motors and their configurations.

I have both a 94 XP and 94 GTX. While more HP sounds like a good thing the factory calibration for the GTX was very spot on if the carbs and pump are in prime shape. It was a very user friendly machine with enough scoot to pull a double tube. Just 5 weeks ago I carried 4 full size adults on mine after my other gtx locked the pump up with a rock 10 miles from the boat launch.

No motor failure..I have enjoyed for about 15 years..Has never had issues with the exception of cranking over and not starting in water last summer..I decided to rebuild carbs..Unfortunately, valve come off when I removed cover..Yes, complete mystery. The only possibility is the original owner had something done..I just find that highly unlikely due to pristine condition when I bought it. He purchased new...If I replace with correct valve, will I run into problems, i.e. carb calibrations, etc, due to the current valve in place all those years..Your info very much appreciated.

 

[AKnarrowback]

Do you know what top speed you have seen out of it? It seems odd that valve is in there. The old saying "if it aint broke don't fix it" comes to mind.

When you rebuilt the carbs did you take notes on the settings? Main jet, pilot jet size, seat size and pop off pressure?

If you say it ran fine for 15 years then I would say you are not going to have a problem throwing it back in and running it. If someone in the past did change it out, and altered any other settings, then changing back to the stock valve might be more trouble than it's worth.

The valve timing procedure is the same regardless of which valve you use, the valve you have is just going to stay open a hair longer. If the motor runs good, top speed is normal, plug color is good then I would stay with that valve until you can confirm if any other changes were made to the machine calibration.

Not a normal situation. My normal answer would be make that thing stock. But if it runs fine then maybe just keep going with it.

I'm used to sleds where anyone that gets into tweaking them NEVER has an all stock configuration so running things a little different, when it comes to calibration, is something I can accept.

My concern would be if the carbs are calibrated to get the most out of the longer duration valve then just throwing a different duration valve in could lean the mixture and hurt the motor if things go the wrong way. Knowing the carb details when you had them apart would help answer the big question of keep or replace the valve.

 

[bevmale]

Do you know what top speed you have seen out of it? It seems odd that valve is in there. The old saying "if it aint broke don't fix it" comes to mind.

When you rebuilt the carbs did you take notes on the settings? Main jet, pilot jet size, seat size and pop off pressure?

If you say it ran fine for 15 years then I would say you are not going to have a problem throwing it back in and running it. If someone in the past did change it out, and altered any other settings, then changing back to the stock valve might be more trouble than it's worth.

The valve timing procedure is the same regardless of which valve you use, the valve you have is just going to stay open a hair longer. If the motor runs good, top speed is normal, plug color is good then I would stay with that valve until you can confirm if any other changes were made to the machine calibration.

Not a normal situation. My normal answer would be make that thing stock. But if it runs fine then maybe just keep going with it.

I'm used to sleds where anyone that gets into tweaking them NEVER has an all stock configuration so running things a little different, when it comes to calibration, is something I can accept.

My concern would be if the carbs are calibrated to get the most out of the longer duration valve then just throwing a different duration valve in could lean the mixture and hurt the motor if things go the wrong way. Knowing the carb details when you had them apart would help answer the big question of keep or replace the valve.

Haven't paid much attention to top speed..Remember reaching 45/50 periodically..Have not rebuilt carbs yet..Just trying to confirm timing is spot on before I dive into carbs..As per manual, assuming I need to set to these specs due to 159 degree valve..
OPENING 149 BTDC +-5
CLOSING 65 ATDC +-5

 

[AKnarrowback]

View attachment 43585

Yes, just follow the manual.

Get both of your marks and then flip the valve to get the closest alignment to the marks, if they are off by a couple of degrees that is okay.

I know some engine builders that would dry fit the case halves to get the closest alignment, for the valve, they could by shifting the rv shaft one tooth at a time in relation to the crank before they sealed the case halves. The same builders would also advance or retard the disk timing on the rv shaft to gain more low end or top end performance depending on their needs. This is why I say running with the different valve, while not ideal, might still be just fine. The rotary valve was really developed to keep the fresh fuel charge from being pushed back out of the case when the piston is coming down.

 

[AKnarrowback]

When finding TDC always do your final setting by rotating the motor in the normal direction it would rotate while running, don't rotate past TDC and then turn the other direction a few degrees to get back to TDC. Remember there is a little slop between the crank and RV shaft, during normal running the crank gear is always pushing into the RV shaft gear. If you hit TDC and rotate back a hair the you have moved the crank but not the RV shaft depending on how far back you turned.

 

[POPPS]

Can some one answer this, I have the 96 shop manual, it has the specs for the 587, 720, and my 785,but no specs on the rotary valve for the 650 engine? And AK is correct, before I pulled the rotary valve on a rebuild, I would put the piston or rod to tdc, and index the rotary valve shaft valve, to save me having to remove, rotate a tooth, insert again, rotate a tooth, again, etc, till I was able to get my disc within specs.

 

[AKnarrowback]

No 657 engine in 96 as far as I know. What model and year are you working on?

 

[bevmale]

View attachment 43585View attachment 43587

Yes, just follow the manual.

Get both of your marks and then flip the valve to get the closest alignment to the marks, if they are off by a couple of degrees that is okay.

I know some engine builders that would dry fit the case halves to get the closest alignment, for the valve, they could by shifting the rv shaft one tooth at a time in relation to the crank before they sealed the case halves. The same builders would also advance or retard the disk timing on the rv shaft to gain more low end or top end performance depending on their needs. This is why I say running with the different valve, while not ideal, might still be just fine. The rotary valve was really developed to keep the fresh fuel charge from being pushed back out of the case when the piston is coming down.

Thank you..Due to the XP valve, assuming I have to follow 159 degree specs.

 

[AKnarrowback]

Yes.