Replacing valve guide bushing in old Briggs 5HP

[creia]

Yeah what KE4 said - but I'd say 6 or 7 thou ain't enough to worry about as far as measurements go (with less clearance, one could easily have valves too tight and bind in guides when engine gets hot! consider thermal expansion rates, I'd want minimum .003 clearance, which means maybe .003 wear, divide by 2 (since you're measuring 2 sides of wear when checking diameter) , and you have maybe .0015" of wear... ) - but as mentioned, the wiggle test comes from experience, and I can attest what KE4 says, you can only really know with more confidence after getting a new valve guide put in (or have a new engine block or short block to compare with) - Once you have done enough comparisons you get a real feel for it , but if I had to really think hard about it how .010" total wear might feel I think it would be getting close to where I might consider new guides, depending on what I expect of the engine in the future (Running hours, type of use, etc) - The plug gauge itself, obviously, allows for .020 total wear (.010 on a side) which to me is rather insane... Also, consider the length of the valve guide itself - a shorter guide will allow a lot more wiggle with less wear than a longer guide will.

I can say, that when I first started doing valve guides (since I had the tools, and it was MY shop so I didn't need boss approval) probably 85% of the ones I replaced didn't need it (In fact, on a couple early ones, the wiggle test got noticeably WORSE after I installed new guides.) Again I never paid that much attention to specs (I didn't have tools to measure bores that small!) but if you really do have just .007 of wear, I think your guides are fine. - Consider, as you said the plug gauge itself means Briggs has a wear limit of .020" on valve guides... so you're well within Briggs' specs, right?

OK- understood and GOOD NEWS! Perhaps I was a bit too conservative on my "wiggle test" conclusions? For now, I will hold off having a new exhaust valve guide installed. First, I'll get the engine running and see what the performance reveals (especially any evidence of oil burning/smoking).
Michael

[creia]

And I just thought of another reference point to compare the wiggle to and that to the amount the intake wiggle in reference to the exhaust. They should have about the same amount when both are new.

FWIW: The INTAKE valve guide measured 0.249" and displayed slightly less "wiggle".
Michael

[bgsengine]

And I just thought of another reference point to compare the wiggle to and that to the amount the intake wiggle in reference to the exhaust. They should have about the same amount when both are new.

FWIW: The INTAKE valve guide measured 0.249" and displayed slightly less "wiggle".
Michael

Sounds about typical for wear - exhaust will usually wear faster than intake, kinda obvious when you think about it..

[creia]

And I just thought of another reference point to compare the wiggle to and that to the amount the intake wiggle in reference to the exhaust. They should have about the same amount when both are new.

FWIW: The INTAKE valve guide measured 0.249" and displayed slightly less "wiggle".
Michael

Sounds about typical for wear - exhaust will usually wear faster than intake, kinda obvious when you think about it..

But of course- HEAT!!
Michael

[Arkie]

It is a judgement call. But consider this, valve guides can wear like cylinders where they are good on one end and bad on the other end. IE tapering and ovaling. This is why go by the wiggle test and just forget that plug test gauge.

I had exhaust valve that would pressurize the crankcase but according the Briggs test plug were fine. This is cause by back pressure in the exhaust. Most of the techs around initially think it got to be a blown head gasket when over have the time it is a worn exhaust valve guide.

Personally if you think it is a lot of wiggle it is most likely worn heavily. Really after doing your first valve stem guide you get a better idea if it is/was or not. You just need a little experience on this.

Good info here about the exhaust valve guide causing the crankcase to pressurize when running. (instead of vacuum)
Never thought of that one.
I've seen guys overhaul a small engine and ignore the valve guides and the engine still smoke and use oil. (intake guide bad usually cause the smoke and oil burning)

[KE4AVB]

I've seen guys overhaul a small engine and ignore the valve guides and the engine still smoke and use oil. (intake guide bad usually cause the smoke and oil burning)

When I first repairing mower for others I would customers swearing they had a bad head gasket or rings when it was just a worn out exhaust valve on the L-head pushing oil out the breather into the carb. Of course they always got a new head gasket.