mower17

valve job

My grampa has a 30 year old murray push mower with a 3.5 hp briggs. He did have trouble starting it and Cheese told me to check the intake valve clearance and sure enough there was zero clearance. So after adjusting that, it started on the second pull. I was pleased with the outcome and also me and my grampa cleaned the carb and replaced the gaskets and diaghram, and that was about one year ago. Well, now my grampa says that it takes about 5 pulls to start. I am thinking about taking the mower to trade school and grinding the valve and seat and then lapping the two together then checking to make sure that both valves are sealing correctly. Would this be something that is a good idea on a mower that is this old? I am sure that by now, the valves have pitted and warped and have some uneven wear. I am sure my grampa doesn't want to put a lot of money into it if any at all so doing a valve job seemed a good idea to me, what do ya'll think? I will also check the air filter and spark plug while I am at it. Anything else that can be done to get it started even easier? One other question I have been wondering, I know 2-stroke mufflers get clogged with carbon over time but do 4-strokes have this problem? Is there any way to clean them out? Thanks for the help!!!!!!!!!!!

jughead

I'd do a compression check to see if reworking the valves would be of any help. If you have 100 lbs of compression, grinding the valves would be good experience, but wouldn't help the 'hard' start engine problem much. If the valve head & seats are indeed nasty your valve guides will probably be worn out as well and will have to be replaced first. You could easily spend 25 to 50 bucks on such a project by the time you buy all the stuff you need.

mower17

I don't have a compression tester of my own so I have no idea what kind of compression it has. I am in the process of making my own leak-down tester. The plan is to just get it to start and run as good as possible for as long as possible since my grampa has two other identical mowers that are in as good or better condition so when this one bites the dust, then he does have two replacements. By any chance, would anybody know if this engine has the thick head gaskets that get damaged when any attempt to remove the head is made or does it have the thin metalic head gasket that can be reused?

snoman

mower17
If you're planning to do anything with a 30 year old mower...the first thing to look at is the piston rings. If they are worn beyond factory specs they will not produce enough vacuum at start up to bring the necessary fuel into the combustion chamber. This can be a main reason for not starting on the first pull.
Why not just do the whole motor,carb(which you said you already did)valves(if need be), seals, ignition,rings and/or piston assy and all gaskets. This way you know everything is going to be up to spec and it will be great experience for you.
I've just finished restoring a 1958 Choremaster mower and I did the complete motor and matched the factory paint and decals...it looks sweet.


snoman

cheese

I agree...it could be valve problems, or it could be a lot of things, like the automatic choke on that carb, or a spark plug, or bad rings and cylinder wear. Could be the ignition system too...30 yrs old, it has points unless it's been updated.

Yes, unless it has been changed in the past 10 years or so, it should have the thick head gasket. Chances are after 30 years, the valves are worn beyond acceptable, the guides probably are too, and the cylinder, etc... unless it has not seen much use during those 3 decades.

mower17

I removed the shroud and turned the flywheel backwards and there wasn't much compression. My grampa said that we will work on it when it doesn't run any more.