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Post by mikboatman on Jul 19, 2006 18:36:58 GMT 1
anybody able to tell me a accurate way to test if a head gasket is blown,need to know what a leak test is any help would be great.
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Post by capnjack on Jul 19, 2006 22:58:02 GMT 1
what engine is it
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Post by mikboatman on Jul 20, 2006 9:03:34 GMT 1
yamaha 30 hp,went out the other day it was pinking a little under load then died,started up again after fifteen minutes.
it was not to hot,paint was not burning so i am not sure if gasket has gone.it was pumping loads of water, impellor three months old .
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Post by malroy on Jul 20, 2006 12:25:43 GMT 1
Using a compression tester can help go some way to diagnosing a blown gasket but it is not foolproof.
When compression is down on recommended readings it can be caused by several things:
Faulty/worn rings, faulty valve gear (4 strokes), damaged porting or leaking gaskets etc.
Following the gauge manufacturers instructions carefully can help point you in the right direction.
The old gas leaking gas test can sometimes help, i.e. put washing up liquid all around the outer edge of the gasket and any bubbling should show a leak to the outside. It will not detect leaks to internal water cooling chambers.
The only real way though is to actually take the head off and look carefully at the gasket.
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Post by mikboatman on Jul 20, 2006 13:57:02 GMT 1
thanks,i have just had a look over the engine today,first chance since the trip.
as i only brought the engine 4 weeks ago second hand.saw it running when i brought it and had tested it once before the problem occured,had a good look plugs dirty/black and no thermastat fitted, one thing i did not think to check when i brought it,so i think engine may have big problem.any advise greatly welcome,accept take up shore fishing...
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Post by malroy on Jul 20, 2006 16:55:08 GMT 1
You do not say, but is it 2 or 4 stroke.
You really need the compression checking. Once you know this is sound then its got to be either fuel or electrics at fault.
Sounds though like fuel starvation.
Pinking is pre-ignition normally associated with incorrect engine timing. Excessive amounts of pinking will lead to overheating and a piston melt down.
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Post by mikboatman on Jul 20, 2006 18:00:07 GMT 1
thank you malroy, it's a 2 stroke 50.1 mix,mix was pre done before filling tank before anyone ask's.
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Post by capnjack on Jul 20, 2006 21:50:14 GMT 1
what fuel are u using how old is the engine approx
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dreadfish
Experienced Full Member
we need a bigger boat
Posts: 98
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Post by dreadfish on Jul 20, 2006 21:53:27 GMT 1
hi capn,engine 1989 model petrol from esso normal unleaded with quicksilver 2 st oil at 50.1,never buy petrol from tesco/asda,etc
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Post by capnjack on Jul 20, 2006 22:10:43 GMT 1
try super unleaded petrol over the years has had octain ratings dropped this can give the impression of poor timing we ave simillar problems with cars
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Post by malroy on Jul 21, 2006 9:17:25 GMT 1
Being a 2 stroke the things I would initially check (some may seem obvious ) would be as follows:
Fuel tank is beathing properly
Fuel line and priming bubble is fully servicable with no air leaks
Fuel pump - I would dismantle and check all is clean and diaphram has no splits.
Carb(s) - dismantle and clean thoroughly, so many get gunged up when left standing over winter without being drained properly.
Check plugs(s) for condition & gapping, check HT lead(s) are dry, clean and not tracking
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Post by mikboatman on Jul 21, 2006 13:45:40 GMT 1
thank you all very much.do you think running engine without thermostat will have caused internal wear?.
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Post by malroy on Jul 21, 2006 14:14:35 GMT 1
The answer regarding wear is double edged.
The thermostat is a control valve to regulate when additional water is let around an engines cylinder block for cooling.
Not having one means that all the cooling water is allowed to fully circulate in the engine from the outset.
Years ago many people used to take them out of their cars in winter so all the water circulated quicker around the cylinders to allow them to warm up quicker.
On the negaitive side it can mean that the engine never reaches its optimum operating temperature quickly which I suppose could result in additional or accelerated wear depending on temperatures.
On the positive side is should mean that an engine is never likely to overheat.
When the "tell tale" stops passing water thru' on an outboard, most people put this down to a worn or faulty impellor, however if you have a thermostat fitted which doesn't open properly (as I have done in the past) this will also keep the water outlet thru' down to a trickle, so not having one at all is better than this situation.
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