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Message |
    
Nick Champion
New member
Username: nickchamp
Post Number: 3
Registered: 08-2006
| | Posted on Sunday, October 07, 2007 - 06:07 pm: | 
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I have a P55 which I have been using for the last three years. The engine always starts very well but the No 2 cylinder oils up over time and eventually dies out. This happens more frequently after low speed running. Looking at the plugs it seems that No 1 cylinder is burning exactly as it should. The ST manual states that the twin engine will run evenly on one cylinder but mine does not. When No 2 dies and the engine is running on No 1 it sounds OK and revs seem OK but as soon as it goes into gear the lack of power is of course noticeable but this is as I understand it should be. If however, when the engine is running normally, I remove No 1 cylinder plug lead so the engine is running on No 2 the revs die right down and unless there is plenty of throttle the engine struugles to keep running.
My question is what is wrong with No 2? I do sometimes get spitting back through the carb but a problem here would surely affect both cylinders. Compression appears to be the same on both so the only thing I can think of is the rear seal although there is no sign of dirty oil in the gearbox oil. So, any ideas anyone? |
Peter Ogborne
Senior Member
Username: peterogborne
Post Number: 225
Registered: 09-2002
| | Posted on Sunday, October 07, 2007 - 07:05 pm: |
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Nick....you don't say if you have put a new set of spark plugs in .If not try a new set,I don't think it would be the seal.Along with a new set of spark plugs check the magneto leads. |
Nick Champion
Member
Username: nickchamp
Post Number: 4
Registered: 08-2006
| | Posted on Monday, October 08, 2007 - 03:56 am: |
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Hello Peter
Thanks for the response. I've tried new plugs and of course when No 2 oils up I need to change the plug to get it going again. At winter maintenance last year I also renewed the HT leads and plug caps as well as cleaning out the expansion chamber. It's a magneto driven engine so I am assuming that the spark is as good on one cylinder as the other as I also put a new distributor cap on and there is only one set of points (which I have not replaced although I did check the gap).The exhaust is clear as it uses a waterlock system and so doesnt foul up much and in any case I cleared the waterlock out completely. I have also tried a hotter plug in no 2 (I use NGK plugs) but it did not make a difference. The boat is now out of the water for the winter but I want to avoid having to take the engine out and do a complete strip down if it can be avoided. I probably would not do that at this stage anyway as No 2 can so far be brought back to life with a change of plugs, but this of course is not ideal, especially where I normally sail with strong tides. What I don't understand is why one cylinder should behave differently when everything would appear to be equal between the two. |
Peter Ogborne
Senior Member
Username: peterogborne
Post Number: 226
Registered: 09-2002
| | Posted on Monday, October 08, 2007 - 06:47 pm: |
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Nick.....have you considered taking off the cylinder head .Check the gasket ,could be a small water leak that is fouling the spark plug. |
Nick Champion
Member
Username: nickchamp
Post Number: 5
Registered: 08-2006
| | Posted on Tuesday, October 09, 2007 - 01:51 am: |
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Peter
Mmm, possible and one I had not considered. Would I still have good compression if the gasket had a leak? Compression is about the same on both cylinders.
It's certainly easier to remove the head to begin with rather than lift out the entire engine I guess as I think I can probably do that in situ. It would give the opportunity to clean out the head waterways properly as well. I have time on my side for a change as I'm now laid up for winter. |
miro forest
Senior Member
Username: miro
Post Number: 295
Registered: 11-2001
| | Posted on Thursday, October 18, 2007 - 01:05 pm: |
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Another possibility is that the number 2 cylinder is too cold while number 1 is good and warm. Most marine engines, in my experience proabaly run too cool.
This difference in cylinder temperature might be enough to make the mixture in number 2 , too rich while the mixture is good for number 1.
Balancing them would be a matter of installing some form of restriction to the cooling water for number 2.
miro |
Nick Champion
Member
Username: nickchamp
Post Number: 9
Registered: 08-2006
| | Posted on Thursday, October 18, 2007 - 01:29 pm: |
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Thanks Miro
It's a possibility I had not considered. The thermostats which ST used, as you probably know, are no longer available anywhere which is why todays head gaskets have some of the waterways blocked. I have not had the head off the engine which is in the boat so I don't know what the gasket is like. If I get to the stage of stripping the engine, which it is starting to look like I shall, it's certainly a point to check. I have tried a hotter plug in No 2 but I don't think that would have an effect if the cylinder is too cold and in any case is probably the wrong way around for this problem. |
Peter Ogborne
Senior Member
Username: peterogborne
Post Number: 227
Registered: 09-2002
| | Posted on Friday, October 19, 2007 - 06:34 am: |
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I still say it is a leaking head gasket.Stuart Turner engines preheat the cooling water by puting it through the exhaust outlet first .I dont thing there would be a temp differential that would effect the running.Take the head off and have a look at the gasket. |
Mike Hodgson
Member
Username: orwot
Post Number: 18
Registered: 10-2005
| | Posted on Friday, October 19, 2007 - 03:26 pm: |
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"Stuart Turner engines preheat the cooling water by putting it through the exhaust outlet first"
Not quite correct
The water is first circulated around the expansion chamber and then to the cylinders and exits outboard via the exhaust.
"Take the head off and have a look at the gasket."
I agree. Do that and you can also check bore/rings water passageways etc
Mike.H |
Mike Hodgson
Member
Username: orwot
Post Number: 19
Registered: 10-2005
| | Posted on Friday, October 19, 2007 - 03:47 pm: |
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Check the exhaust port on No2 is clear and not partially blocked with carbon deposits.
Any restriction here will seriously impair performance .
Mike.H. |
Nick Champion
Member
Username: nickchamp
Post Number: 10
Registered: 08-2006
| | Posted on Friday, October 19, 2007 - 05:55 pm: |
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Peter & Mike
Yep. It looks like I'm going to have to get the head off to check. Trouble is I will need to remove the engine to do this as space is a bit tight but I'm now out for the winter so I shall have time in the next few months.
I don't think the problem is blocked exhaust ports as I managed to clean out the expansion chamber last year and the ports were clear then. I've only run about one hundred hours since so it should not have gummed up too much in that time.
On a slighly different note I may replace the P55 when I take it out with my rebuilt P66 and then totally strip the 55. However the 66 has a "new" 73 type gearbox and the 55 is the old tram handle type. This means a new shaft as the length is less but does anyone know if the actual alignment is the same between the engines, which is what I am hoping as then I just need a longer shaft and drop the 66 in on the old 55 bed fixings. What drawings I have from the standard manuals don't make it clear (at least not to me). |
Peter Ogborne
Senior Member
Username: peterogborne
Post Number: 228
Registered: 09-2002
| | Posted on Friday, October 19, 2007 - 07:11 pm: |
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I wont argue about the degree of correctness except to say that the cooling water enters the exhaust outlet first and then goes to the expansion chamber.
However this is all academic and does not really have much to do with Nicks problem......must be very ''tight'' in the engine room if it hard too get the head off. |
John Archibald
Member
Username: john_archibald
Post Number: 26
Registered: 08-2006
| | Posted on Friday, October 19, 2007 - 07:28 pm: |
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Maybe you can run the engine or turn it over with some soapy water on the head / cylinder interface and watch for bubbles. Might not need to take the head off then.
Archibald
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Peter Ogborne
Senior Member
Username: peterogborne
Post Number: 229
Registered: 09-2002
| | Posted on Saturday, October 20, 2007 - 07:43 pm: |
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Sorry John what i mean to convey is that there might be a water leak from the water jacket into the combustion chamber on number 2 cylinder.Experience has shown that corrosion occurs around the edges of the water ways in the head and it is not the best seal on the gasket when it gets to a certain stage. Small leaks externaly would not present a big problem,not the sort that Nick is having.....a little water into the combustion chamber will sooon short out the plug |
