looper overheat

[parrfive]

Ive got a problem that ive haven?t come across before. Im working on a 130 looper that has a overheat problem. We remover the thermostat covers after doing all the normal things and were getting exhaust smoke and pressure coming out of them. Leak down is fine. Anyone out there ever have this problem?

 

[ezeke]

Re: looper overheat

The thermostat area is cast-in, so you most likely have a blown cylinder head gasket or seal. Leak down tests on a 2 stroke looper (or crossflow) are of questionable value because you have to keep the piston above both sets of ports so you can't tell what is happening on the downstroke, period. What did you get on the compression tests?

 

[parrfive]

Re: looper overheat

I agree with you on your lack of faith with the leak down. It was simply done at top dead on all four to check heads and casting. I'm a Yamaha service manager and have been working on all models for 30 years and this is a first. The heads and the power head have been off and inspected with no visible signs of oil in the water jackets. Im beginning to wonder if this isn?t normal because of where the discharge water dumps in the exhaust guide. I don?t have access to the o.m.c. Rep line so im flying blind. Any other help would be much appreciated.

 

[Dhadley]

Re: looper overheat

We'll assume the pump is OK and you've probably removed the unit and installed a hose to make sure water can flow properly.

When you start the motor with the t-stat cover off, how long do you let it run?

 

[parrfive]

Re: looper overheat

Water flow is not a problem. I get exhaust smoke and exhaust pressure immediately after starting. Im sure the exhaust in the water jackets is what causing the overheat. it does this with and without the lower unit on.

 

[parrfive]

Re: looper overheat

The pressure I was referring to was out of the thermostat cover in case it wasn?t clear.

 

[Dhadley]

Re: looper overheat

OK, it takes a bit of time for those blocks to fill up and get water flowing out of the t-stat area with the covers off. Seeing some exhaust / smoke in there isn't unusual. It's coming up from the water exit rather than being in the incoming water. I agree with the leakdown, if it's holding then the head gaskets are probably OK. Good idea.

What is the issue? Is the hot horn coming on at some point?

 

[parrfive]

Re: looper overheat

Yeah the costumer complaint was almost an immediate horn. After 30 years it?s gotten very difficult to believe much they say weather it be ignorance or other. Tank tested and got a fairly quick horn. Temp gun reveled star head hot. Im on the lower TX. Coast with very warm water temps so everything down here seem to run on the ragged edge of an overheat.

 

[parrfive]

Re: looper overheat

I decided to have my mechanic reinstall the powerhead. Before he installed it we put two corks that were shipped with a reman powerhead I received last week in the two water dump holes in the exhaust guide. After starting no more smoke but still a bit of pressure. All I can figure is that it?s the design of the engine for the water psi to keep the exhaust out.

 

[Dhadley]

Re: looper overheat

It's not uncommon for those heads to get a film built up inside the water passage just like the Yamahas do. Usually some carb cleaner or CLR cleans them out. When we run into this with loopers we clean both heads and then put them back on opposite sides. If the overheat follows the head we reclean again or replace that head.

Don't worry about the pressure, it's coming back up from where the water would dump. It'll stop once water is flowing.

Are the vernatherms that you're using black or white?

 

[parrfive]

Re: looper overheat

They?re white and new and tested. Down here for lack of a better term the build up is called brown tide. I do about 50 sets of Yamaha heads a year because of it. I?ve also been for the last several years? acid flushing with great success. I don?t recommend that method for a layman as u can melt a motor. Thanks again for your help and input.

 

[Dhadley]

Re: looper overheat

White? Ok, they're probably the old style and need some attention. The original white ones had 3 little "feet" on the end where they go into the grommet. Salt & crud gets built up behind the grommet and grabs the "feet" which doesn't allow the vernetherm off the seat and let the water flow.

Couple solutions, you can trim the "feet" off so the cone of the vernatherm sits on the grommet, not in it, or get the new style black one. Hard to believe an old white one is still around. And it sure shouldn't be in that late of a model motor.