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10335 Possibly low compression?

#1

E

EdBrown

I recently purchased a Lawnboy 10335, and it really looks good. It ran okay, but I put in a new ignition coil, since it had the original from 1999 when new. After replacing coil, and new spark plug, it will not start. It seems to be that it has low compression when I use the pull cord.

If the compression is low, what has to be replaced to bring it back up? I can fix some things on the Lawnboys, but this has stumped me.
Any advice will be appreciated very much.


#2

Two-Stroke

Two-Stroke

Did you change anything else when you installed the coil and plug? It had good compression before those changes -- right?


#3

E

EdBrown

Two-Stroke said:
Did you change anything else when you installed the coil and plug? It had good compression before those changes -- right?
Click to expand...

I am not sure. It did start when I got it, but the pull was not as strong as I think it should be. I installed only new spark plug, and the coil, and these were installed correctly. I was just wondering if the compression is low, what causes that? Thanks.


#4

P

Phototone

You got 2 things to be concerned about, firstly the compression of the cylinder/piston which is determined by the rings and wear on the piston and cylinder walls. Secondly you have the reed valves which have to seal tight on the pistons down-stroke, and the crankcase has to be air-tight, which means the crankshaft seals have to be good. If you didn't change the seals, then I would change them. While you have the crankcase split, take the part the reed plate is attached to (that the carb screws into), and clean or wipe off the surface, and put your mouth to the hole where the carb is fitted. Blow and suck on the reed assembly. It should let you blow, but you shouldn't be able to suck much, if at all. If this condition is ok, then just replace the crankcase seals, if the reeds pass air both directions, then replace the reeds too. Don't forget to apply sealer to the crankcase halves before re-assembly. I use form-a-gasket #2, but that may not be the best thing, but it works for me. I have found Lawnboy 2-cycle mowers will run moderately well with weak compression if the whole intake process is good and tight. (reeds and seals), and the carb/intake gasket is good and airtight. I use form-a-gasket on this paper gasket to help get a good seal too!!


#5

impalass

impalass

Phototone said:
You got 2 things to be concerned about, firstly the compression of the cylinder/piston which is determined by the rings and wear on the piston and cylinder walls. Secondly you have the reed valves which have to seal tight on the pistons down-stroke, and the crankcase has to be air-tight, which means the crankshaft seals have to be good. If you didn't change the seals, then I would change them. While you have the crankcase split, take the part the reed plate is attached to (that the carb screws into), and clean or wipe off the surface, and put your mouth to the hole where the carb is fitted. Blow and suck on the reed assembly. It should let you blow, but you shouldn't be able to suck much, if at all. If this condition is ok, then just replace the crankcase seals, if the reeds pass air both directions, then replace the reeds too. Don't forget to apply sealer to the crankcase halves before re-assembly. I use form-a-gasket #2, but that may not be the best thing, but it works for me. I have found Lawnboy 2-cycle mowers will run moderately well with weak compression if the whole intake process is good and tight. (reeds and seals), and the carb/intake gasket is good and airtight. I use form-a-gasket on this paper gasket to help get a good seal too!!
Click to expand...
I have a lawn boy engine with 55psi and it will run but no power.


#6

E

EdBrown

impalass said:
I have a lawn boy engine with 55psi and it will run but no power.
Click to expand...

Thanks very much for your advice. This is probably over my head to do this, and I may just take to Lawnboy dealer. It is a good mower, and I wanted to use it next spring. Thanks again.


#7

turfboy1997

turfboy1997

EdBrown said:
Thanks very much for your advice. This is probably over my head to do this, and I may just take to Lawnboy dealer. It is a good mower, and I wanted to use it next spring. Thanks again.
Click to expand...

This model is a Tecumseh four stroke if my research is correct. If my memory is correct compression is supposed to be between 60 and 90 psi to run. If you are having issues it might be better to find a donor mower with another similar engine or a briggs if you don't want a 2 cycle. I have had experience switching all of these engines to the silver series self propelled decks with little of no issues. My best advice for you is to become your own lawn boy mechanic because they are going to laugh at you when you take it in the door or they are going to try to rip you off for repairs. I have a complete engine just like that in my back yard with plenty of compression. I will never use it because i only bought it for everything but the engine. If you want it message me and we will make arrangements to make it yours. But first i would go get a compression checker at an auto parts store and see what the reading is. Hope this helps!


#8

E

EdBrown

turfboy1997 said:
This model is a Tecumseh four stroke if my research is correct. If my memory is correct compression is supposed to be between 60 and 90 psi to run. If you are having issues it might be better to find a donor mower with another similar engine or a briggs if you don't want a 2 cycle. I have had experience switching all of these engines to the silver series self propelled decks with little of no issues. My best advice for you is to become your own lawn boy mechanic because they are going to laugh at you when you take it in the door or they are going to try to rip you off for repairs. I have a complete engine just like that in my back yard with plenty of compression. I will never use it because i only bought it for everything but the engine. If you want it message me and we will make arrangements to make it yours. But first i would go get a compression checker at an auto parts store and see what the reading is. Hope this helps!
Click to expand...


Good news. My 10335 starts just fine. I rechecked my newly installed coil, and one of the screws to tighten it down has slipped back a little. I thought I had tightened them okay, but apparently not enough on one. Anyway, when I regauged it with a business card, and tightened it good, it roared back to life like it did before. Evidently, was not low compression, as it runs very good now.

Many thanks to all for the advice. I certainly appreciate it.


#9

beg

beg

techumseh 4 stroke?Buy a compression tester.that motor has a tedency to eat head gaskets.


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