Valve guide repair

bthughesOctober 8, 2010

I need to repair the exhaust valve guide on a Briggs and Stratton L-head, aluminum block, #220707. There is a bushing which is loose and can be easily removed. I figure the guide was repaired with a bushing and later the bushing came loose, or was never tight. The engine diagram refers to two different guides, one called "Guide -- Exhaust Valve" and the other, with a note "Guide -- Exhaust Valve or Intake (Brass)". When I look up these parts with the part numbers, they are called "valve guide bushings". I fully understand the bushing process and the tools involved. I do not understand what the guides in a new engine consist of. I have not found any reference to replacing the guide. Does the new engine have a guide pressed into the aluminum, which is repaired by reaming and bushing? Are a valve guide and a valve guide bushing the same thing? I would not expect a replacement bushing to fit any better than the one that is in there now.

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walt2002

Well tried to post a message earlier, will try again.

On consumer type B&S engines, the valve guide is milled into the block casting. When this wears out, you put in a valve guide bushing. It has been a while but I believe the brass valve guide bushings you mentioned are larger OD than the other ones and so a larger counter bore for them which should take care of the looseness you mention. Of course you need the correct tools to properly install these, counter bore reamer, driver (you can improvise this) and finish reamer. Both reamers must be used with the proper guides. Valve should be re-seated or at least lapped in afterward.

Walt Conner

    Bookmark   October 8, 2010 at 9:50PM
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bthughes

Thanks, Walt. In all of my research I have not seen any reference to an oversize bushing or any kind of insert that could be use to repair an existing repair. I do not want to buy every available bushing to see if one works. I was prepared to peen the old bushing in place just to see if it solved my problem of firing (backfiring?) through the exhaust. I decided to not mess around like that, but if I can't find a more high-tech solution, that is what I will do. If the engine works well, then I will continue to search and figure out how to restore the valve train to good condition. It is the original engine and I want it working like new.

    Bookmark   October 11, 2010 at 9:13AM
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walt2002

"In all of my research I have not seen any reference to an oversize bushing or any kind of insert that could be use to repair an existing repair."

It is simply a matter of the type of valve guide bushing used, it was not intended as an "oversize" bushing, just happened that way.

Walt Conner

    Bookmark   October 11, 2010 at 6:11PM
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bthughes

Walt -- I see how I could have worded that differently. Oops. I did clearly understood what you said, that there are several bushings, and you think that at least one of them may be fatter, and fit the hole better. I went straight from that and expressed my frustration at being unable to nail down some accurate data. The suppliers have to have accurate numbers when you order parts, type and code numbers are indispensable, the company gives you tons of specifications down to thousanths of an inch, every thing is quantified in no uncertain terms. But not this little thing (and probably some others). Come to think of it, I have not read of any other instance of a bushing coming loose. I guess I will have to become the expert on this situation. What I have decided is to get the tools -- I anticipate using them a lot -- and a sampling of bushings, and see if one will serve my purpose. So, many thanks to you, Walt, for helping me get closer to a solution, or to a plan at least. Please stay tuned. By the way, the bushing in question has a chamfer on both ends, and looks like the drawings of an iron sintered bearing, which someone said was discontinued because it caused various problems.

    Bookmark   October 11, 2010 at 9:28PM
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mforest

I had a very similar issue with my engine.

But I needed a short term repair and i didn't have the time to wait to get a new valve and bushing.

In any case I couldn't see how to get the old bushing out except by reaming it all away. I tried pulling it up abut it seems to be pressed into the block.

The wear on the valve stem was about 15 - 18 thou. and it allowed the valve to wiggle quite a bit.

So I got out my pinch knurling tool and simply knurled up the area of the valve stem that was worn really badly.
I was able to get about 12 thou. .

I then polished the knurled area and I ended up with a valve that wasn't so sloppy. I then lapped the valve into the seat.
It seem to work OK.

I expect that I can get 20-30 hours of running time before it all goes sloppy again.

    Bookmark   November 25, 2012 at 7:44AM
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mownie(7)

I may have missed something back in my early days when I was just getting into the automotive mechanics field. Back then we would knurl the INSIDE of the valve GUIDE and then run a finish reamer through it to accomplish what you did.
I never heard of anyone knurling a valve STEM. That must be one heck of a knurling tool to work a valve stem like that.
We also would knurl the skirt area of pistons to give them a tighter fit when they wore enough to need it.
Of course, that was back in the old days when I would occasionally hear a car owner brag that his car "has nearly 60,000 miles on it and is sill going strong. Yes sir, I've only had to replace the head gasket one time". :^)

    Bookmark   November 25, 2012 at 9:59AM
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mforest

I still face the task of removing the worn valve guide.
Do you think I could tap the guide with say a 5/16 thread ( the guide ID is 0.250 or thereabouts) and then pull it out?

    Bookmark   November 25, 2012 at 10:48AM
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mforest

Here's a picture of my pinch knurling tool.
It is handheld and squeezed onto the shaft while the shaft to be knurled is rotated. I can use a drill to rotated the shaft ( either hand held or drill press)
It might not be the most accurate thing in the world, but it fills my needs.

In the background you can see the Briggs.

    Bookmark   November 25, 2012 at 11:02AM
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mownie(7)

forest, the valve guide I.D. on your engine is 1/4" (as you said, .250).
The Briggs service manual states to use a 7mm tap to thread the guide for their puller.
Of course you can improvise by making your own puller if you are quite handy (and it looks like you might be).
If you do not already have the Briggs service manual for your engine, send me an e-mail and I will take care of that.

    Bookmark   November 25, 2012 at 4:03PM
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