Leaky Valve Seat

[KE4AVB]

Briggs 12J707-1753-E1

What I have appears to be a leaky intake valve seat. It not loose that I can tell but the leakdown indicates a leaky intake. Resurfaced valve and seat using valve grinding compound and also set valve clearance which cure part of the problem. Compression went from 30 to 45 psi after I did the resurfacing of both valves but the leakdown still indicates leaky intake and the only I can think of right now is a valve seat leaking around its outside mating surface.

The service manual talks about pinging in a loose new valve seat and wondering if this would work with the old seat that appears to leaking.

Now the history of this engine is that it is used in very harsh conditions at a nursery. They have already ran it without oil twice, warp the head from overheating due lack of air flow, and broke several pull ropes all in the last 6 months. When it came this week it would not start with the operator barely able pull the engine over. What I found was oil that is as thick as 90w gear oil, another blown heat gasket and this intake leak. Once I got that thick goo was clean out of the engine at it now will pull through; although, it still feel tight. For what this engine been through the cylinder is a lot better shape on this 98 than the 2013 that they also brought in running rough.

I feel just like wringing their necks some days.

[bgsengine]

why not do a liquid test? set engine so valve heads face up , pour in a bit of rubbing alcohol, (or gas I guess but careful with that) and watch where the liquid leaks through. - Even cutting the valve seat and refacing or replacing the valve, and lapping it in is no guarantee of a good seal if the guides do not hold valve true to the seat

[KE4AVB]

Maybe I should used a torch to see if it was leaking.

That the strange thing about it liquid isn't seeping through as I done tried the fuel test just leaking under air pressure; of course, the liquid test is a gravity test. That's why I wondering what is going here as air is definitely coming of the intake at the carburetor and not PCV line so it not piston blow by.

Hmmm, it may be a worn valve guide but I did cycle the valves several times and don't see the valve hanging or wooble as it closes after installing the springs before doing the liquid test.

I can an put in a valve guide and new valve. The current aluminum guide currently is only slightly loose and would easily pass the no go test; although, I have seen exhaust guides to cause smoking problems even when they pass the same test. It will probably be Thursday before I can as the valve and gasket set that I ordered should in late Wednesday unless the Briggs warehouse backorder them.

[KE4AVB]

I came up another to test for the leak which show it leaking all around the seat or valve face to various degrees under pressure. Will try the new valve guide and valve. If that don't and considering the cost of the tools to do a one off seat replacement I think I see if customer is willing to install a new engine instead especially since it needs a complete overhaul. It they had oil in them this time. 7 engines and counting this year.

The only thing is they are going to need two engines as when I look at the Husqvarna 325HWT that is only a couple years old it needing replacement too. Cylinder damage too great to cleanup. It had a completely clogged air filter and looks like dirt got inhaled pass it somehow. The pre-filter is actually mud caked. Here's what I found in the filter box.

[Arkie]

IMHO:
If I seen someone CONSTANTLY neglecting engines PM (ran low on oil, no oil changes, breathers clogged and them knowing the engines are running in a harsh environment that requires PM or anything else like that I would not even consider doing a major repair on their engines or equipment unless they can readily accept the fact that new equipment replacements are going to be required to keep them up and running. It would be just asking for future problems about being blamed that their worn out eq was not being repaired correctly, etc.
I would just tell them in a nice way they need new engine replacements and maybe they would finally see that it's their fault for the failures instead of the guy doing the repairs. It appears that they think their time is better spent making money elsewhere and therefore they need to pay the price for their neglect IMHO.

[KE4AVB]

Totally agree...There is only so much miracle work we can do.

[bgsengine]

I came up another to test for the leak which show it leaking all around the seat or valve face to various degrees under pressure. Will try the new valve guide and valve.

Consider the possibility of a weak valve spring?

[KE4AVB]

Customer killed the project as the engine was in need of overhauling or replacement. They can get a complete mower for less less what a replacement engine would have been. They are just going to replace both mowers at the same time.