AJS & Matchless Owners Club

Trying to be brief. Ha ha! Has anyone experience of these little engines?

History
Friend was given a Flymo Rotovator as part payment for some work. Wouldn't start there was a suspicion it had been given two stroke mix instead of straight petrol. I need use of rotovator so said, get it to the lock up I'll get it going.

Cleaned filthy plug, healthy spark. Hardly any fuel in so topped up with fresh petrol and shook it around a lot. It tried to kick but no start. Plug pretty much dry. Poured a little very small amount of petrol in plug hole. Started and ran but not very nicely. Plug completely fouled up again.

Today
Go and try again after downloading manual. See there's problem with the choke, PO had also altered carb spring arrangment for vane type governor and removed and taped over the cut off. No start and arm getting tired. Get exasperated as just want it running to try and get the carb right. Pour a little petrol in the plug hole again. Pull string several times. Faint puffs of smoke but not kick in. A little more petrol in plug hole. Pull string, engine locks up and string handle pulled out of hand as a result. Surely not enough fluid to hydraulic the engine!

Now have the head off, loads of carbon. Valves out, exhaust valve and seat black as pitch inlet not to pretty either. Piston stuck two thirds of way up bore. Lose patience, get the rubber mallet, put it on piston crown and tap with very small ball pein hammer. Piston moves down a bit. Spanner on crankshaft end, a bit of movement. Tap, jiggle. Tap, jiggle. Everything frees up. Bit of oil in bore, which is ok - ish. All smoothly turning.

Tempted to just clean the valves up, lap them in, stick it back together, amend the carb as per manual instead of PO arrangement and see what happens. Only thing that puzzles me is the odd extension piece that is shown in the parts list as bolted to the big end cap and I wonder if something has "gone wrong" in the crankcase but not inclined to explore it or really do anything too much because I think that it needs new valves, guides if there are any and a carb refurb kit.

Shout at me.

Johnny B

If it has a weird "extension piece" on the big end, it's probably one of those primitive splash oiler things. I think it's called a "rod dipper". Amazes me how they don't break off...

I have a similar 3 1/2 hp B &S engined Hayterette Mower.

It can be temperamental at times.


Have you checked the carb diaphragm? If it hasn't split, it needs to be tensioned slightly on reassembly. Obviously blow all the orifices out as well, preferably with carb cleaner as well. Keep carb cleaner well away from the diaphragm.


I also suggest trying to start it without the air filter element, maybe with a little choke. It sounds a bit weird, but even when the mixture is ok this will get mine going normally.


The next thing to check is the mag, and then the points/condenser if it's an older model. You'll need a flywheel puller for that. Briggsbits is a great source of parts too.


Andy

Smash that engine to bits with a 7pound sledge hammer. You will immediately feel a zen calm pervading your central core. Replace it with a Honda static engine equivalent and live the rest of your days in contentment. It's the only way.

I'd realised that it was probably a oiler type thing later that night afytr making the original post.

Also realised that although I may've (?) put more petrol in than I thought there was no way I could hydraulic it as the valves were so crap they would have just let it squirt by.

14 pound lump hammer has previously been close to coming into play before, BMW R65, not near that yet. If I can just get a couple of days use out of it that will do. Honda engine would be no use as the B&S forms the backbone of the tool and all the ancilliary bits structured to fit.

Johnny B

John, I've got the impression that you said the engine locked up/piston stuck in cylinder but that seems unlikely unless there's some serious breakage.
It occurs to me that p'raps it was the pull-start mechanism that was jamming, not the engine itself..............

Just what I thought, Sprid, so I took the recoil starter off and applied a spanner to the end of the crankshaft with no joy.

As often happens, this further discussion has made me wonder if something had got jammed in the alternator. They are quite exposed with a simple tin cover. At home at the mo' but will take a look for witness marks tomorrow. Hope I find some!

Charging up the battery drill so I can get a wire brush on the valves at the lock up. Those keyhole type valve spring retainers are fun.

Thanks for the interest.

Johnny B

UPDATE

Valves cleaned up, lapped in (just about) and replaced. Re-assembled and started although again only with a teaspoon of petrol down the plug hole to get the initial go. Running better than it was but clearly, as Dave T suggests, there's work to do on the carb.

The manual(s) I've downloaded are a bit short of carb info. I assume that there's some kind of suction arrangement as the carb is immediately above the tank. Also puzzled by the tube running from the valve chest to the carb as if that plays a part is really loose at the "rubber" connectors.

I'll do some more internet searching.

Johnny B

Dave T wrote:Smash that engine to bits with a 7pound sledge hammer. You will immediately feel a zen calm pervading your central core. Replace it with a Honda static engine equivalent and live the rest of your days in contentment. It's the only way.

and if you need a witness, I know someone who will be for a small consideration.

56G80S wrote:UPDATE Valves cleaned up, lapped in (just about) and replaced. Re-assembled and started although again only with a teaspoon of petrol down the plug hole to get the initial go. Running better than it was but clearly, as Dave T suggests, there's work to do on the carb.

John, it's too easy with an unknown engine to go off at a tangent with diverse diagnoses and become distracted from the basics. Clearly the valves were in a sorry state, but I agree that it sounds like a fuel shortage problem. If the machine had been fed two-smoke mix as is suspected and then stood for some time the petrol will have evaporated leaving oil blocking up the carb jets and drillings (never mind the ethanol gum problem). I'm not sure if it's relevant but I believe that two-smoke carb needles are a different profile from those for 4-strokes.
The pump diaphragm may also be split.