4th Engine in 99 TSL 770

[Seapg]

I just bought a 99 ski with 770 engine. The engine has been replaced 4 times by the previous owner (professional installation) using SBT engine. Rear cylinder keeps failing. I got it cheap because the current low hour engine lost power and compression in rear cylinder (135 front, 70 rear) and owner was tired of paying the installation costs. I pulled head and the gasket was blown. Cylinder looked good, but plug was almost clean. Front plug looked good and plenty of oil there apparently. Only has one carburetor. What could be causing this repeated failure? Oh, I noticed that it had two head gaskets on it? What is the reason for this? To reduce compression? Do I need to replace with two gaskets? Plan to go premix once I replace gasket. Maybe this will help. Perhaps one of you experts out there can save me here. Thx

[Technical Support]

Re: 4th Engine in 99 TSL 770

If the oil pump has not yet been replaced or removed, that would be my first guess. Without good digital pictures of the pistons and other parts, no one can give you much further direction.


We do not use two head gaskets, it's a double layer gasket.

[Seapg]

Re: 4th Engine in 99 TSL 770

This is a very low hour SBT motor. I replaced the blown head gasket and compression was good at about 140 each cylinder. Installed a block off plate and ran 40:1 premix. Ran beautifully for about 10 gallons of gas....then blew head gasket again....this time "zero" compression in rear cylinder (was 60 first time). Will pull head soon for further inspection. I am thinking that the surfacing should be milled on head and block since it isn't oil related or overheating. Is this a problem with Tigershark 770 motors?.....Only one carb...not two. Thx

[Technical Support]

Re: 4th Engine in 99 TSL 770

There are no common 770 problems, but you obviously have something external causing it. As I said 3 months ago, we needs pics of the pistons and parts.

[dank]

Re: 4th Engine in 99 TSL 770

I have seen cylinder heads on the 770's become warped from overheating. When you have it off take it to a machine shop to get it resurfaced.

[Seapg]

Re: 4th Engine in 99 TSL 770

Thanks, Dank. My thoughts too. Plugs were nice and dark/oily. Don't think it is a lean condition or lube related. Cylinders were pretty. I'm thinking the block should be surfaced, too since it has some small imperfections in the spot where it failed before. This is an awesome ski and I want to get beyond this problem.

[titanic]

Re: 4th Engine in 99 TSL 770

After smoothing the head cover, I used copper gasket sealant around the new head gasket after blowing through a replacement in 35 hours. After that, never a problem.

[Seapg]

Re: 4th Engine in 99 TSL 770

Oh, boy! Thx for the responses so far. Guess I've got some other problems. I pulled the head and the copper gasket sealer was pretty awesome...head gasket not blown this time. Found a hole in center of the rear piston with cylinder walls nice and smooth. Will pull engine the engine and see if I have any other piston damage. Doesn't look like it at this point. Something in this ski is eating motors. One carb....so will pull it apart, etc and make sure I have no obstructions and look for air leak source. Perhaps a cracked intake manifold or something. I feel it is external to basic motor since this is 4th engine. Plenty of coolant water coming out and engine didn't seem hot at all. Whew! Any ideas such as getting a larger hi speed jet in carb? Premix oil/gas already.

[Technical Support]

Re: 4th Engine in 99 TSL 770

I agreee, that sounds like an air leak, possibly in the intake, possibly the carb itself. Your crank is toast also, if you burned a hole though.

[Seapg]

Re: 4th Engine in 99 TSL 770

I've just now gotten around to pressure testing my engine prior to teardown. There was a good size air leak on either side of the front oil seal along the crankcase seam. But the rear piston had the hole burned in it. Does this sound right? No leak found in rear that I could see. Question....When pressure testing, how does the air get to both front and rear through the one pulse fitting? Through reed valves and intake manifold? Thanks for any input.

[Technical Support]

Re: 4th Engine in 99 TSL 770

You don't pressure check through the pulse in that case. You have to have a block off plate with an inlet, and block off the pulse.