MTD Tractor Starting problem

[lefty]

Sounds like a plan. I'll do it today and post back. Thank you.

[lefty]

So right now the clearance on the intake is .004.

I don't exactly recall what I set it at before but I think the specs are .003-.005.

Knowing how I operate, I probably would have picked .004 because it's in the middle. But I can't recall exactly the final setting was that because It always moves when I tighten down the screw and I have to do it like 5 times to get it to hold within spec range. So it's very possible that my target was .004 but it ultimately ended up at .005 and I accepted it.

Anyway. Maybe try it at a tight .006?

In the meantime, I'll probably pull plastic manifold for a good inspection and oring.

Can I use a gasket maker in lieu of a gasket for this valve cover? No going to be able to get one today or tomorrow either.

[Arkie]

Can I use a gasket maker in lieu of a gasket for this valve cover? No going to be able to get one today or tomorrow either.


Yep,

You Might even just leave the cover off and give it a crank and watch the intake valve movement and be ready to kill it if it starts. You can also right after you adjust the valve lash gently push up and down on the intake valve and see if the lash always comes back to the same on your gauge. Those valve springs are weak and you can do this by finger pressure or suing a tool to push on it. this is too make sure it's not sticking part open or?????
If your lash changes the valve stem is sticky

Have you tried removing the spark plug and squirting a spoonful of gas into the cylinder, apply full throttle with no choke and see if direct injection of fuel will make it hit a lick????

If it does hit a lick or fire this may indicate the intake valve is not always sealing and allowing a good suction of fuel into the cylinder when cranking for start.

All of these tests is too see how the engine acts when trying to start if it gets fuel into the cylinder.
You said before that the spark plug ALWAYS looked dry when it would not start.

[lefty]

I adjusted the intake to .006 and still the same. No problem with starter at .006.

I checked the valves several times and they seem to be holding their clearance. I worked the valves by hand and I'm not noticing any sticking. I also tried to inspect that when I had the head off to lap them. I was looking for any sticking or play.

But it did start right up after putting a little gas through the spark plug hole. So we're getting close. So I'm guessing this could be a problem with either valve? Exhaust not sealing during the intake stroke maybe?

I'm confused though because I just lapped the valves and am getting solid scores on my leak down.

I'm no engineer, not much of a mechanic either with my inexperience, but why wouldn't they put the decomp bump on the exhaust valve, especially with such a long intake manifold? Gas needs an Uber to get from the carb to the cylinder.

[Arkie]

I adjusted the intake to .006 and still the same. No problem with starter at .006.

I checked the valves several times and they seem to be holding their clearance. I worked the valves by hand and I'm not noticing any sticking. I also tried to inspect that when I had the head off to lap them. I was looking for any sticking or play.

But it did start right up after putting a little gas through the spark plug hole. So we're getting close. So I'm guessing this could be a problem with either valve? Exhaust not sealing during the intake stroke maybe?

I'm confused though because I just lapped the valves and am getting solid scores on my leak down.

I'm no engineer, not much of a mechanic either with my inexperience, but why wouldn't they put the decomp bump on the exhaust valve, especially with such a long intake manifold? Gas needs an Uber to get from the carb to the cylinder.

Just a couple thoughts.
I would probably hook up my leak down tester and get the engine 1/4 inch past TDC, (OR at the TDC area setting recommended by Briggs for when adjusting the valves on that engine) Lock the flywheel and inject air and use my finger and gently push open the intake valve and try to wiggle it slightly as it closed by it's own spring pressure. Do not let it snap shut hard. You are trying to see if the valve is always seating good and checking for guide wear.

OR maybe first keep on opening up the clearance on the intake valve to see if you can get it to suck fuel. Open it up to where the decompression is causing the starter to lock or hang then go the other way reducing the intake valve clearance.?????????????
If you do not ever get the engine to hanging up on the intake stroke maybe the lobe is worn on the cam or the decompression is ?????maybe someone with chime in with a second opinion.

If dumping fuel into the cylinder gets a run then you either have a intake valve issue or for some reason the decompression is coming in too soon on the intake stroke???????????

I would confirm that dumping fuel into the cylinder (by removing the spark plug) always gets a good startup first before testing other things, just to make sure I'm not getting side tracked and led astray. (which happens to me quite often)
Be gentle when re-installing the plug, I've know of some of them plug threads eventually stripping out if you tighten it little too much each time into the aluminum, they even strip sometimes coming out.

Also you are going to have to keep the bat charged up and do not overcrank the starter, you are probably about to lose the starter or the fiber bendix gear already from crank testing.
AND if you want to save your bat charger ALWAYS unhook one lead or unplug it BEFORE cranking the engine. (even if it's the type that says it's a crank charger) Cranking while the charger is connected is what wipes out (KILLS) 99% of bat chargers and if the manual even lists a warning as such it will say do not crank the engine over 5 SECONDS with the charger connected.
If a engine won't start after the battery is charged and the charger disconnected, the cranking system needs immediate repair before continuing, instead of burning up the charger.

[Arkie]

Might have to see if anyone knows how much the lift should be on the intake valve when at 0 clearance. If you could find out such you could actually measure the Cam lift at the rocker arm area to indicate that the cam lobe is ok or reject.
This lift measurement would let you know if the intake cam lobe is worn down enough to result in the intake valve not opening far enough and staying open long enough on the intake stroke which would allow the decompression to come in too soon and stay in longer resulting in fuel blow back in the intake manifold. (maybe) Just a thought ??????????????
If the cam lift is not enough you can probably never INCREASE the intake valve clearance enough to make any difference in making it SUCK gas. (because the decompression comes in too soon due to not enough lift)

If the cams lobe tip is worn down you could try to take the intake valve clearance to very minimum. Do make sure you always have some clearance or you will break/bend something.

[38racing]

Am I missing something here but doesn't increasing the valve clearance reduce the maximum opening height of the valve. I would think you would reduce the clearance to get maximum lift. Although there might be more compression release but that all happens just at the end of the compression stroke. If your problem is lack of fuel sucked in then you want to increase/extend valve opening on the intake stroke.

[lefty]

I can try that as well. Maybe I take the head off again and have another go at the valves?

[Arkie]

Am I missing something here but doesn't increasing the valve clearance reduce the maximum opening height of the valve. I would think you would reduce the clearance to get maximum lift. Although there might be more compression release but that all happens just at the end of the compression stroke. If your problem is lack of fuel sucked in then you want to increase/extend valve opening on the intake stroke.

Right we ALL seem too be missing something here trying to get a clue as to his start issues possibly due to weak intake suction.

At first I thought maybe the compression release was coming in too soon on the compression stroke with the lower valve lash settings for some reason. (like the cam lobe not correct or valve not repeating seating sealing correctly.

But since he says the engine is not kicking back or stalling like it should be doing with the valve clearance past max specs, after thinking about the possibility of the valve not opening up enough for some reason ???and not staying open long enough during the intake stroke he should try reducing the valve clearance to very minimum and give it a try. (since increasing the valve clearance did not even get a hard crank or starter stall on the compression stroke might be another clue that the engine is not even getting enough intake AIR to cause a compression lock stall.???????????? I would think that the compression should be somewhat weak if it won't indicate any compression stall.

I would not pull the head just too look. Check the leak down as suggested by opening and closing the valve manually while the leak down gauges are connected and injecting air with the engine locked in place securely. (could be a loose valve SEAT that you missed before)[/b]
IMHO: I would have to have more info before I just pulled the head again to look.

And maybe if none of the above produces any results see if you can find some specs on how much lift the intake cam lobe should have and the duration in degrees of how long the intake valve should stay open/closed. The amount lift can be easily checked once it's know.

But first leave all as is and direct inject gas again into the cylinder and test for a re-start.

[KE4AVB]

Anyone gave any thought that it maybe a worn cam lobe on that 793880. I just replaced my first one where the engine actually ran although not good where the exhaust was worn nearly round.