30hp tohatsu rebuild

[daniel944]

Hi all

I have a 2006 30 2 stroke tohatsu. Faults are it refuses to idle but does everything else fine. I have always serviced this motor myself so tried to tune it up. New plugs fitted and tried to tune the carb to nil effect. Compression test reveals 120psi in the top cylinder and 150psi in the bottom

So I'm hoping all she needs is a head gasket (there is a small amount of corrosion around the area the head meets the block). 

I have rebuilt heaps of 4 stroke automotive engines but no 2 strokes. Does anyone have any advice? 

[daniel944]

How would blocked jets cause one cylinder to be down on compression? 

[jeffb5.8]

The blocked jets or carby issue would be causing the non idling issues. 

The reduce compression in the top cylinder would just be reduced performance and possible contributing to the idle issue, I doubt a head gasket would fix the compression issue, would probably need rings done or a rebuilt.

i guess you need to weight up the cost to rebuild Versus sell the motor and replace and update the motor.

 

[daniel944]

Hi all, I pulled the carb off and apart. Looks like new inside so I put it back on and restarted. Straight away I noticed she was worse and no amount of carb adjustment made any difference. I got the compression tester out again and the top cylinder had dropped another 10 psi. That was enough to convince me that the head gasket is definitely leaking. 

After disassembly the problem is very clear. I must say I am shocked. This is a motor that has been flushed after every single use and aren't tohatsus supposed to be bullet proof??? 

 

Edited February 13, 2017 by daniel944

[jeffb5.8]

how many hours on the motor, what do the Pistons and bore look like.

Edited February 13, 2017 by jeffb5.8
Pictures worked

[macca02]

I have a 2007 25hp 2 stroke tohatsu, which I believe is the same motor. So probably should check the compression on mine aswell! That's a bit of a worry, I'm not too mechanically minded but is it just the gasket that needs doing or does it need to be rebuilt?

[daniel944]

Not sure why pick aren't visible, I can see them?

Rebuild is definitely required. I have shown engine to a machinest today and he has picked up some light scoring of the bottom cylinder saying the rings have started grabbing. Interestingly it was the top cylinder that had the head gasket blow through. 

Also I noticed the thermostat had a lot of crud around it, even though it.was letting water through when flushing perhaps it was constricted. Either way a new thermostat and water pump will be fitted. 

Carb was cleaned and blowen out with compressed air. As I mentioned before it looked like new inside. 

Edited February 13, 2017 by daniel944

[jeffb5.8]

3 hours ago, daniel944 said:

Not sure why pick aren't visible, I can see them?

Rebuild is definitely required. I have shown engine to a machinest today and he has picked up some light scoring of the bottom cylinder saying the rings have started grabbing. Interestingly it was the top cylinder that had the head gasket blow through. 

Also I noticed the thermostat had a lot of crud around it, even though it.was letting water through when flushing perhaps it was constricted. Either way a new thermostat and water pump will be fitted. 

Carb was cleaned and blowen out with compressed air. As I mentioned before it looked like new inside. 

Sounds like your on the right track, be a good project thread to watch the build and progress to the end.

[kingfishbig]

The head gasket should be replaced after 10 years as a precaution. Ie a failure is on the cards after 10 years of use. If it fails it can let water into the engine. If the crankshaft bearing start to rust then the engine won't last even if the pistons and bores are rebuilt. So I would ask your mechanic about this before spending anything on the motor.