Briggs 500 Series - Interesting troubleshooting case for the pros. help needed.

[motormonkey]

I don't feel that .003 is too great a clearance, but I would like to kno how you got that. You should have measured the valve stem with a mic at multiple places in the travel area. There should be no more than .001 difference in any of the measurements. You the measure the valve guide at the top, center and bottom with a small hole guage and mic. Again you should have no more than .001 difference between any measurements. The difference between the valve stem measurement and the valve guide measurement is your clearance.

Second, you never said what was the cause of the valve sticking in the first place and what corrective action you took. If the valve was bent or the guide tapered, you are spending a lot of time and effort for nothing.

Rivet, you are right.... I didn't say the cause of the valve sticking did i?

I know this much.. the issue is in the head... the valve wasn't bent, and the tappets aren't bent either... the cam.. showed some wear... I will try to get a few pictures tomorrow of the pieces... I am going to tear it down again....

I DID clean it up thoroughly(Head and piston head/block also the cylinder wall is spotless.)... sanding the valve stems lightly and lubing them before putting them back in.. after that, they moved beautifully in the valve guide.

This is a unique situation as I am currently traveling in a third world country... and I cannot get replacement parts here can't order them in either... international shipment costs like $100 bucks just to get a letter.

I was lucky to find a business that custom makes gaskets so I took the old headgasket and they made me a new one.

Update on the problem: I unstuck the valve via the valve spring access door and got the mower to run horribly for 30 seconds...
then to restart it I had to continue pulling the rope to kind of Help it stay running.. (it was running very slowly, obviously slow enough for me to pull the recoil along with it every 3 seconds to keep it running)


I guess it is also possible I got the valve tappets reversed... though that wouldn't explain the valve sticking in the head.. the only thing I can think of is the head is warped... and something happens with the expansion of the metal(perhaps exaggerating the warp in the valve guide when it heats up...?

this is frustrating trying to get it diagnosed correctly.. again, i'll try to take some pictures perhaps tomorrow maybe that will lead to some insight.

thanks everyone for your replies in the discussion.

 

[reynoldston]

I all my years of doing this work I never seen a valve stick unless there was a reason for it. rust? Broken valve spring? valve guide got hit some how? If the valve stem or valve guide aren't damage and you do have some stem clearance its something I sure don't understand. You said you are using homemade gaskets, maybe the gasket is too thin and the valve is hitting? A valve in a valve guide is a very simple mechanical thing. I am sure someone here has your answer.

 

[motormonkey]

I all my years of doing this work I never seen a valve stick unless there was a reason for it. rust? Broken valve spring? valve guide got hit some how? If the valve stem or valve guide aren't damage and you do have some stem clearance its something I sure don't understand. You said you are using homemade gaskets, maybe the gasket is too thin and the valve is hitting? A valve in a valve guide is a very simple mechanical thing. I am sure someone here has your answer.

reynoldston,

I should have clarified... the gasket I had fabricated was done by a professional gasket maker.. they used the same material as the stock gaskets. that metal material in the middle with the gasket material surrounding it. same mic thickness.

I will try to get a video of the head while turning the flywheel.

 

[motoman]

Motor, Reread your original description...When the Intek cam was replaced I had to press off the drive gear from the cam. I don't remember exactly, but it must have been keyed. Could your cam have somehow sheared the cam drive gear key. So depending on heat the gear is spun outside the cam , making an index sound. Then when heat/cold allows the cam operates the valves, but out of time??:confused2:

 

[motormonkey]

Motor, Reread your original description...When the Intek cam was replaced I had to press off the drive gear from the cam. I don't remember exactly, but it must have been keyed. Could your cam have somehow sheared the cam drive gear key. So depending on heat the gear is spun outside the cam , making an index sound. Then when heat/cold allows the cam operates the valves, but out of time??:confused2:

motoman,

That is a VERY interesting question.....

I will check that I have to tear it back down today...

Here is the video of manual rotation of the flywheel with the head off... i know this doesn't do a lot for us except we can see the timing etc.

 

[hsherm]

After reading and re-reading your post, it sounds like the valves are not getting enough oil on them, thereby causing them to heat up and expand just enough to stick. Something you may want to check.
Just an observation is all.

 

[motormonkey]

Well hsherm,

UPDATE: I worked the valve over with WD-40 and it doesn't stick any more...

I wish I would have gotten a video of how it started up, because I can't find anything on youtube or the web in general that acts like it nor info on other similar cases.

but.. when I try to start the mower, it half-way starts up... I don't know how to describe it... basically.. I can pull the starter rope and it fires and runs for 1 second VERY slowly, (the Speed of the pull is the only way I know to describe it) then it dies.. I can almost keep it running if I keep pulling on the rope in time with the mower... it's going that slow.. and I dont get a LOT of resistence..

SO.. I am thinking my head-gasket is bad. I don't have any other conclusion if I had a compression gauge I would know but I don't right now.

I'm having a head gasket made for it and will be picking it up monday. (it's hand-made by an Artisan since there are none available and it costs $100+ in shipping to get one in where I am at right now)

After reading and re-reading your post, it sounds like the valves are not getting enough oil on them, thereby causing them to heat up and expand just enough to stick. Something you may want to check.
Just an observation is all.

 

[hsherm]

Thanks for sharing the video! I just watched it a few times (actually, quite a few times), and noticed a couple of things. The timing seems to be off by one "notch". (degree?) For example, the exhaust valve starts to open just before the piston reaches Bottom Dead Center (B.D.C), allowing for air and oil to be drawn into the combustion chamber. (The chamber acts as a vacuum at this point due to the combustion.) This then throws off the intake valve by the same amount; thereby lessening the amount of fuel that can be drawn in. I also noticed a slight amount of oil in the piston cylinder. This could be caused by bad rings, but it's more than likely caused by the "vacuum" effect drawing in air and oil through the exhaust port due to the exhaust valve opening before B.D.C.
It's been awhile since I've actually worked on small engines (mainly due to health reasons), so I'm making these observations from memory.
I hope this helps.

 

[motormonkey]

hsherm,

I am going to take another video of the timing for you while I have the head off.. I did get my head gasket back today though.

I think I am going to have to tear it down and re-time it because it seems way farther off than before.. and I might have to put a different cam in it (I think I have one from an identical spare parts mower.) though it did seem like it would have ran great if it weren't from low compression. I'll try to make a video and post it for you to see what you think.

Hey don't worry about making the observations from memory, I appreciate any ideas/help I receive.


Best Regards.

Thanks for sharing the video! I just watched it a few times (actually, quite a few times), and noticed a couple of things. The timing seems to be off by one "notch". (degree?) For example, the exhaust valve starts to open just before the piston reaches Bottom Dead Center (B.D.C), allowing for air and oil to be drawn into the combustion chamber. (The chamber acts as a vacuum at this point due to the combustion.) This then throws off the intake valve by the same amount; thereby lessening the amount of fuel that can be drawn in. I also noticed a slight amount of oil in the piston cylinder. This could be caused by bad rings, but it's more than likely caused by the "vacuum" effect drawing in air and oil through the exhaust port due to the exhaust valve opening before B.D.C.
It's been awhile since I've actually worked on small engines (mainly due to health reasons), so I'm making these observations from memory.
I hope this helps.

 

[Polaraco]

knurl valve guides to reduce the ID

Now that you said something about it I remember that also. Its been a few years back for me and my memory isn't as good anymore. I still got the tools to grind valves but don't remember the last time I used them. On the small engines I just clean them up with grinding compound any more, I think they make valves and seats of better material now then in the older days. I don't care what is said older isn't better newer is.

I was going to say that. Thanks

When you put the valve back in the head, did slide up and down OK

Did you put some oil on the valve stem when you put it back in?

Poor mans valve grinding compound. Sand and grease. If it's an over head valve, you can use a electric drill. There's a 62 Chrysler 413 running around for 10 years now with that done to the heads.