MTD Tractor Starting problem

[lefty]

Tough to tell given how it came off but that was the area that looked the worst.

While the head was off, I held it upside down and put some gas into it to see if it held. I saw a video online showing that this may a good way to see if the valves are leaking and since I was losing air out of the intake, sure enough, the fuel leaked out down past the valve into the intake. So I lapped the valves and it's doing much better but still leaking just a tiny bit. So I'll do it again tomorrow. Could this have been the problem? I was thinking about it while walking the dogs and given my need to understand exactly why with everything...I came to this conclusion (probably wrong as usual but here goes).

This machine has a 6" long plastic intake pipe between the carb and the head so during cranking, it takes a few revolutions of the cycle for a usable mixture to make it to the cylinder. But during the compression stroke, I'm getting air moving back out toward the carb. So I'm ending up with a combustible mixture sloshing back and forth too far from the head and never quite making it to the combustion chamber because of the air escaping out the intake valve. When I spray carb cleaner in there, it's enough to get things started, and once going, there's enough flow for it to run well. The times when it did start, I just got lucky in that when the engine last stopped, it happened to be at a point in the cycle that allowed enough mixture to make it there before it started getting blown back out.

Am I close?

[bgsengine]

You're close, but when you go to lap the valves again - make sure you carefully check the valve seats to see if they may have come loose. Also, carefully inspect valve guides - these engines are known for valve guides shifting out of place (if they do , it's usually pretty obvious) , and if you have loose seats, and/or shifted guides, you may wish to consider replacing the head. You'll also want to check the head gasket surface for flatness or warpage.

and yes, the leaking intake valve can cause your hard starting problem - based on your symptoms however, I'd want to look very carefully at the seats and be sure they are not loose - valve seats can pop out and hang valve open, then suddenly slip back in place and she starts up again.

[lefty]

I took another run at lapping the valves again this morning. Whilst having it apart, I inspected the seats and guides for any sign of movement or misalignment. Nothing jumped out at me as being out of wack. The seats appear to be firmly in place and wouldn't budge while pulling on them pretty hard with my fingers. Valve guides look strait and in place and seem to be firmly seated. Valve stems appear strait.

The lapping went well in that visually, everything looked smooth with no pitting or anything obvious to me. I tested again with gas in the upside-down head and this time it's leaking ever so slightly. I left the gas in there for about 20 minutes and when I came back, the level appeared the same. There was, however, a bit of a sheen to the stem when looking through the intake port. Indicating that the stem may be slightly damp but there was no fuel running down out of the port. So I'm guessing a tiny bit is getting by. This is a major improvement from where I started but not perfect.

Trying to figure out what to do next...take another run at it with lapping? I have a local shop that I'm sure if I brought the head to them, they would grind the seats for me and sell me a set of valves. Or I could replace the head, as you suggested. If we don't think a 3rd lapping is going to seal it off for good, should I give it a run as is? This is my own machine. Like I said, it's not my primary machine and I don't cut with it. This is hobby/learning time for me on this one.

Thank you.

[bgsengine]

doing that gas test with the valve springs installed? If all you got is a little dampness down valve stem after 20 minutes of sitting you're good to go as far as valves are concerned.. If it got to the point you were thinking of having a machine shop do things up and new valves (or if you found you might need new valves) I'd go with a complete head set (Last I knew of the head set came complete with valves already assembled and all new components for assembly - gaskets, a re-designed shroud, instruction sheet for the set, etc etc.)

[lefty]

Thank you Sir. I was hoping you'd say that. I'll button her up and see where we're at. Just waiting on my new head gasket.

[Arkie]

Just my 2 cents worth.

Don't let seeing the gas churning in the carb throat of those Briggs engines lead you astray, it's a normal thing on several of the Briggs engines even when all is correct and the engine just cranking fast.

[lefty]

I finished this one today and everything is running great. Thank you.

[Arkie]

I finished this one today and everything is running great. Thank you.

Lefty:
Just wondering what lap process did you use when lapping your Over head valves?
(did you use the rubber suction cup method of spinning the valves head with a variable speed drill or what?)

Redneck method I use for OHV type heads that reduces the manual labor and speeds the lap process:

Reason I asked is I use a short section of heavy wall gas line hose or hydraulic hose clamped onto the valve stem and a dowel bolt into the hose and connected to a bat operated variable speed drill and pull gently on the slow speed drill while spinning the valve slow. The hose connection allows for flex and you can just push the stem forward every once in awhile to check the valves face and apply the lapping compound.

Lapping the old l-head valves (valves in head) manually is not a fun thing and I usually end up using a bat operated drill but getting a good rubber cup connection to some valves heads in not easy. I have several different sizes of the rubber cups and usually have to keep testing until I find a cup that will stick good.

[creia]

Arkie,
Where do you purchase the "good rubber cups"? I lap a lot of the old Briggs and Tecumseh flatheads and find that the suction cups that come on those lapping sticks are not very good. Does anybody have a link to any lapping sticks that have GOOD suction cups?
Michael

[lefty]

I used the manual process. I saw the other process on youtube and was a little frightened by it. This is only the 3rd or 4th set of valves that I've ever lapped so I'm always a little timid. I'm learning that one of the big differences between an experienced and knowledgeable mechanic and a rookie is knowing how hard to hit things. Knowing how much force and speed is appropriate for each situation.

The suction cup has always given me a hard time but I've come up with a workable, but a gross, solution. I lick the cup. It hangs on for quite some time when I do that and when it pops off, a take another lick. Probably not the healthiest way to do it but it seems to work for me. I have the luxury of time as a hobbyist. I usually only have about 1 or 2 projects in the shop at any given time. I know a lot of you guys are running businesses and time is money.

All that being said, maybe I'll employ the drill next time.