98 ts 770

RLR · 10-05-2009, 06:24 PM

Hi, I just winterized the ski last week..And decided to take a compression test before fogging her...I dont know which is CYC 1(I figure its the one with the shortest plug wire) i got a reading of 95 psi, and the second was 110 psi...My question is, is this normal.. Would I have to be looking toward a piston rebuild kit...If so would I have to get the engine bored for the new pistons..How much would this cost? Or is even worth fixing.. Thanks.

engr146 · 10-05-2009, 07:35 PM

PM dank! for best info.and parts ,But my 98 770 TSL is 150# each cylinder standard compression Mag+PTO
Yes It"s worth fixing! top end ,is a very very common ,procedure ,they sell top end kits @ SBT 2 pistons rings and bearings gaskets in one kit,and many machine shop can bore .25 over
the new pistons come setup for your bored head.

dank · 10-05-2009, 11:19 PM

That sounds low but check your gauge on another ski first to see if it is accurate. 150 is normal and less than 105 will be very hard to start. If it is accurate then pull the head first so you can inspect the head gasket. It is normal for a 770 to need a head gasket after a few years. With the head off you can check the cylinder walls and the top of the pistons. Post pictures if possible for more advise.

RLR · 10-06-2009, 02:39 PM

Yeah, I figured the PSI seemed pretty low...It wont start without me giving it gas, and smokes a little... How would low compression affect performance? When I did have it in the water about a month ago, it seemed fine...Had it up to about 42mph...Well ill start tinkering with it now, before it gets too cold out here...Will post pics later....Another question am I better off pulling the whole engine out or doing the work with engine still intact.

dank · 10-06-2009, 05:35 PM

Low compression will give you an overall los of HP the more load on the engine the more it will show. On a TS770 42 is slow it should be @50mph if everything else is in good condition.

engr146 · 10-06-2009, 05:36 PM

I'm looking foreward to seeing pics!! I live in Lynn,MA real close to RI

RLR · 10-08-2009, 06:01 PM

Hey, I took another compression test since the first time I didn't open throttle...Now im getting a reading of 120/ 110..Anyways I still took of the head to take a look at pistons and cyclinder walls..Take a look and let me know what you guys think...

Oh and are the head gaskets suppose to be riveted together, shown on the last pic...

lownrangr · 10-08-2009, 06:14 PM

the first pic it looks like you had some overheating in that mag cylinder at some point in time. The pistons don't look bad, but that clean spot on dome on the head kinda looks suspicious. Which piston goes with the funky dome, the lighter or darker one? And which cylinder had 110 psi? How do your cylinder walls look?

RLR · 10-08-2009, 06:33 PM

The piston on the rear towards the shaft is the one that has the weird build up, and the front piston toward the bow of the ski is reading 110 psi...The cyclinder walls dont look bad at all, no scrapes of grooves on them...Are the gaskets suppose to be riveted together, or as two seperate pieces? There like aluminum or something...

engr146 · 10-08-2009, 07:40 PM

Thanks for posting Pics,Now I will have something to go by! I 'm waiting to here what
Dank and lownrangr have to say,after seeing these Pics!
THX

What's up w/the riveted gaskets,looks and sounds strange .