I placed an SBT engine in a 98 GTI this past August. My experience with SBT was great and I thought that the machine was running very well. We only managed to ride for about 15 hours before our northeastern US watercraft season has pretty much ended. I thought that as part of the winterization process, I would measure and record the compression each season.
This is where my surprise came. I measured the Mag cylinder first and got 140 PSI, then measured the PTO cylinder and only got 115 PSI. I assumed I must be doing something wrong so I decided to measure it several times under different conditions and got the following.
Engine Cold: .......Mag: 135 PSI ........PTO: 110 PSI
Engine Warm: ......Mag: 140 PSI .......PTO: 115 PSI
Warm with ..........Mag: 145 PSI .......PTO: 123 PSI
Sea-Doo Lube
sprayed in
Cylinders
Warm again .........Mag: 138 PSI .......PTO: 115 PSI
With Lube
burned off
I cannot vouch for the accuracy of my gauge, but the difference remained fairly consistent. I never checked the compression prior to this time, but the lower compression in the PTO cylinder correlates with my noticing that right from the start, whenever I checked or replaced the sparkplugs, the PTO plug was always darker.
Could this be the result of an engine assembly defect? Since I am not very hard on this machine (very little WOT) might the compression still improve on the low cylinder with additional ride time or is it sure to be broken in by 15 hours?
Typically when a question like this is asked, one of the first replies then asks about what did the original engine fail from. Well, I learned a lot with the purchase of this machine. The original engine failed a few hours of riding time after I purchased the machine. When a dealer friend and I tore the engine down we found a seemingly classic water ingestion induced crank bearing failure with bearing debris pitting on the head and pistons. The previous owner was apparently less than honest when I had asked if the machine ever experienced any water ingestion.
Sorry for the long post, but I wanted to accurately describe where I was at and looking for suggestions on what I might do next. Thank you in advance for your time taken to read this.
Tim
This is where my surprise came. I measured the Mag cylinder first and got 140 PSI, then measured the PTO cylinder and only got 115 PSI. I assumed I must be doing something wrong so I decided to measure it several times under different conditions and got the following.
Engine Cold: .......Mag: 135 PSI ........PTO: 110 PSI
Engine Warm: ......Mag: 140 PSI .......PTO: 115 PSI
Warm with ..........Mag: 145 PSI .......PTO: 123 PSI
Sea-Doo Lube
sprayed in
Cylinders
Warm again .........Mag: 138 PSI .......PTO: 115 PSI
With Lube
burned off
I cannot vouch for the accuracy of my gauge, but the difference remained fairly consistent. I never checked the compression prior to this time, but the lower compression in the PTO cylinder correlates with my noticing that right from the start, whenever I checked or replaced the sparkplugs, the PTO plug was always darker.
Could this be the result of an engine assembly defect? Since I am not very hard on this machine (very little WOT) might the compression still improve on the low cylinder with additional ride time or is it sure to be broken in by 15 hours?
Typically when a question like this is asked, one of the first replies then asks about what did the original engine fail from. Well, I learned a lot with the purchase of this machine. The original engine failed a few hours of riding time after I purchased the machine. When a dealer friend and I tore the engine down we found a seemingly classic water ingestion induced crank bearing failure with bearing debris pitting on the head and pistons. The previous owner was apparently less than honest when I had asked if the machine ever experienced any water ingestion.
Sorry for the long post, but I wanted to accurately describe where I was at and looking for suggestions on what I might do next. Thank you in advance for your time taken to read this.
Tim
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