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Low Compression - Kawasaki FR730V
#1
S
scottchopchop
S
scottchopchop
Low Compression - Kawasaki FR730V
The engine is probably 10 years old.
Last mow of last season and suddenly one cylinder #1 stopped firing. (left, fuel pump side)
Pulled the valve cover off and the push rod was completely disconnected and also bent.
The bolt holding the rocker arm bracket to the head had become very loose, that bolt had almost completely backed out, and so the entire rocker assembly was flopping around.
Nothing else looked particularly dysfunctional.
Replaced the push rod and adjusted the valves on both cylinders.
However, it's not running quite right. It takes maybe 10 or 20 seconds for cylinder 1 to start firing. The engine starts up but with only cylinder #2 firing and then 10 seconds later before cylinder #1 finally kicks in.
Put on new coils and that didn't solve the problem.
Checked compression:
Cylinder 1 (low)
100 psi (cold engine) and it holds...doesn't drop pressure
125 psi (warmed up engine) and it holds...doesn't drop pressure
Cylinder 2 (within specs)
150 psi (cold engine) and it holds...doesn't drop pressure
170 psi (warmed up engine) and it holds...doesn't drop pressure
On that final mowing last season, when the problem began, I had been dealing with a bad bearing on a deck spindle, it had been grinding and that blade was rotating very slowly....just throwing this in the conversation because I suppose this could have been dragging the motor down and potentially caused overheating with my faulty cylinder #1.
The head gasket on #1 has been leaking just a bit of oil for a couple of years, but didn't seem to affect the compression or performance prior.
I pulled head #1 off and to my untrained eye, the only thing that seems obviously out of place was the blown head gasket...it was now blown in two spots.
To my eye, both valves seem to be seating fine and nothing with them seems loose, or sticky.
I do notice, when looking through the intake and exhaust ports on head #1, that the valve guide on the intake protrudes perhaps 1/8 inch, while the valve guide on the exhaust port protrudes perhaps 3/8 inch. I don't know the specs, perhaps this is normal? Or perhaps one or both of these valve guides got hot and slid out of place...and perhaps this is the source of the low compression?
Would that blown head gasket be enough to cause the low compression? Should I replace it and see what happens?
Or am I likely looking at something else wrong with the valves, seats, guides, etc etc...and I should go ahead and just replace the head/valves,etc with new ???
Pics of head attached.
Lastly, the cylinder itself looks great to me...no scratches, no scoring .... very smooth ...nothing obvious to indicate to me an issue with the rings.
My inclination is to just throw on a whole new head assembly, with new valves and seats and etc. Those complete head assemblies are about $300-$350 now....so a bit of an expensive experiment if it doesn't solve the problem.
Any thoughts or advice appreciated.
www.lawnmowerforum.com
The engine is probably 10 years old.
Last mow of last season and suddenly one cylinder #1 stopped firing. (left, fuel pump side)
Pulled the valve cover off and the push rod was completely disconnected and also bent.
The bolt holding the rocker arm bracket to the head had become very loose, that bolt had almost completely backed out, and so the entire rocker assembly was flopping around.
Nothing else looked particularly dysfunctional.
Replaced the push rod and adjusted the valves on both cylinders.
However, it's not running quite right. It takes maybe 10 or 20 seconds for cylinder 1 to start firing. The engine starts up but with only cylinder #2 firing and then 10 seconds later before cylinder #1 finally kicks in.
Put on new coils and that didn't solve the problem.
Checked compression:
Cylinder 1 (low)
100 psi (cold engine) and it holds...doesn't drop pressure
125 psi (warmed up engine) and it holds...doesn't drop pressure
Cylinder 2 (within specs)
150 psi (cold engine) and it holds...doesn't drop pressure
170 psi (warmed up engine) and it holds...doesn't drop pressure
On that final mowing last season, when the problem began, I had been dealing with a bad bearing on a deck spindle, it had been grinding and that blade was rotating very slowly....just throwing this in the conversation because I suppose this could have been dragging the motor down and potentially caused overheating with my faulty cylinder #1.
The head gasket on #1 has been leaking just a bit of oil for a couple of years, but didn't seem to affect the compression or performance prior.
I pulled head #1 off and to my untrained eye, the only thing that seems obviously out of place was the blown head gasket...it was now blown in two spots.
To my eye, both valves seem to be seating fine and nothing with them seems loose, or sticky.
I do notice, when looking through the intake and exhaust ports on head #1, that the valve guide on the intake protrudes perhaps 1/8 inch, while the valve guide on the exhaust port protrudes perhaps 3/8 inch. I don't know the specs, perhaps this is normal? Or perhaps one or both of these valve guides got hot and slid out of place...and perhaps this is the source of the low compression?
Would that blown head gasket be enough to cause the low compression? Should I replace it and see what happens?
Or am I likely looking at something else wrong with the valves, seats, guides, etc etc...and I should go ahead and just replace the head/valves,etc with new ???
Pics of head attached.
Lastly, the cylinder itself looks great to me...no scratches, no scoring .... very smooth ...nothing obvious to indicate to me an issue with the rings.
My inclination is to just throw on a whole new head assembly, with new valves and seats and etc. Those complete head assemblies are about $300-$350 now....so a bit of an expensive experiment if it doesn't solve the problem.
Any thoughts or advice appreciated.
IMG_20250305_070347201 (1).jpg
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