It's not astronimy related.. or is it?

[bojan]

Recently I made a mistake when I tried to clean the rotor of my lawn mower so I leaned the machine at 90° angle (to the wrong side?) and the oil from carter went into cylinder (via valve compartment ?).
I had to expel the liquid through the spark plug hole to be able to use it at all (obviously, the presence of oil prevented the piston to move when both valves were closed).. The motor was working for some time after that mishap.

But.. it died on me last Friday.. Wouldn't start again, no compression at all.

The theory is, a solid piece of burnt oil (there is a lot of it in the cylinder, see pictures) went into a gap between exhaust valve and head ( I didn't find it, yet).

Is there an easy way to remove the stuff without damage to the head and block ?
Also, there are two scratches (marked) on the cylinder.. I can feel them with finger.. not sure if they are the other cause for low compression.


PS
How is all that related to astronomy? Well.. The day has only 24 hours.. and If I am using available time on repairing this engine, I can't do astronomy :-)

[Leo.G]

If the scores are big enough to feel you will have compression issues, even new rings and piston won't fix that. If the cylinder isn't too badly scored with fingernail catching score marks a quick hone and a new set of rings could improve compression.
The solid carbon you can remove with a scraper or soft wire brush. If it's not the gasket mating surface you don't need to be as particular as to how gentle you are and a wire brush on a drill will do it as long as you don't gouge it into the alloy.

I'm sure you'd know the old trick of a little oil down the plug hole, if it boosts compression the rings are shot.
If the score marks aren't too bad even just new rings may give your engine enough life to mow and maintain the yard without bothering to hone the bore.
As mentioned lower, let me know which engine and I can see if I can hunt a standard ring set up, if they are laying around as old stock I may be able to get them cheap or free.

EDIT: Top left side of head (gasket surface) just below head mount hole (second image), that isn't a crack in the cylinder head is it?
It could just be a hair or something but if it's a visible crack as it appears the head is shot and you'll never get compression.


To remove the solid oil/carbon possibly jamming the exhaust valve open turn the crank until the exhaust valve is opened and use a compressor to blow the obstruction out. You can also spray carby cleaner in which will help break the carbon up, I use brake cleaner or carby cleaner to do that, whatever is at hand. Just flush the crank out with old oil before putting fresh oil in to use the mower.
Oh, WD40 will also break it up slowly.
If it's carbon build up on the valve seat your are best off removing the valve. Few people lap valves these days, I'm past it but you could use a soft wire brush and carefully clean the seat, or grab some fine to medium valve grinding paste (very expensive now) and a lapping tool and clean it up that way.
You could have some laying around, it's also used to frost glass (or used to be used for that).


Always tilt the mower to the exhaust side (carburettor up) to prevent this issue with 4 stroke mowers.


A friend who owns a local mower shop has 34 acres with so many old mowers for parts. If you were in Sydney the chances are I'd be able to get you a good replacement engine basically free. Freight to Victoria would be a killer.


If you give me the engine model I'll see if I can hunt up a service manual online?
They are mostly available free for Briggs and Victa engines.


Good luck!

[Saturnine]

Hi Bojan
The motor doesn't look very healthy, at the very least it needs to be stripped down, cleaned and reconditioned. The scratches in the bore would need to be honed or lightly skimmed as well though the loss of compression may not be critical.
May well be nearly as cheap and less work, to buy a new machine, how long have you had the current mower, looks a "few" years old, Briggs & Stratton motors did have a good reputation .

[bojan]

Thank you both for the replies..

Yes, this is pretty old machine a friend gave to me 10 years ago because he didn't want to throw it away :-)
Maybe I should give up and leave it on the grass in front of the house.. but first I will try to clean it, after all the test can be done after only 8 screws are to be tightened ...

[Leo.G]

Torque the head down properly to do the oil compression test or leak down test (compressed air in spark plug hole via one way valve).
Though that wouldn't tell you anything if the valves are leaking, it wouldn't hold any pressure.

[fsphotography]

Blown head gasket Bojan.
Frank.

[bojan]

After cleaning and close inspection yesterday, I found a spiral burr in the cylinder emerging under the piston.. My guess is, broken ring(s), and new scratches of the the cylinder are the culprit for the lack of compression...
Definitely the time for new lawn mover.
I am thinking of electric one (Bunnings, 1.5kW, 240VAC, $150), my lawn is not that big so this machine should do.