Replacing valve guide bushing in old Briggs 5HP

[creia]

1967 Briggs "Koolbore", horizontal shaft
M- 130202
T- 135-01
C- 6712087

The exhaust valve guide is excessively worn as determined by my side-to-side "wiggle test". It needs a new bushing installed. I have read up on how to do it in my repair manual. That being said, it requires me to purchase a number of special Briggs tools (some NLA) so I am deciding to have a machine shop I have used for other tasks do the job for me.
Research shows that the replacement bushing is Briggs # 63709 (readily available). My plan is to purchase the OEM Briggs bushing and supply it to the machine shop.
Here is my question to those of you that have done this before...
Once the new bushing is installed, does the ID of the new bushing need to be reamed to get the proper clearance with the valve stem, or is it "plug and play" meaning that it requires no internal reaming and is ready to go with the proper clearance? If the former, what is the specified clearance/tolerance? Would the machine shop know what it should be or would they expect me to provide that spec to them?
Looking forward to the education, as always.
Michael

[RoyM]

The valve will go in nicely but the guide will still need to be finish reamed or said valve will seize when it gets hot. I learned that the hard way.

[KE4AVB]

I get the initial reamer size and the finish reamer sizes later this morning. Just got to wait until the coffee kicks in so I don't break my neck getting the reamer set for the 1/4" valves. They are in the bottom of my tool box as I haven't used them in five years.

I made my last bushings for an engine here as I want heavier side walls of the brass bushings. This requires a larger reamer to start with. At one time I was able to get some after market bushings that were already thinker than the Briggs bushings. But TEW has been out of business for sometime now. The Briggs bushing are fairly thin walled so you might want to get a couple for each guide as they can get damage on install and have to be replaced.

[creia]

I get the initial reamer size and the finish reamer sizes later this morning. Just got to wait until the coffee kicks in so I don't break my neck getting the reamer set for the 1/4" valves. They are in the bottom of my tool box as I haven't used them in five years.

I made my last bushings for an engine here as I want heavier side walls of the brass bushings. This requires a larger reamer to start with. At one time I was able to get some after market bushings that were already thinker than the Briggs bushings. But TEW has been out of business for sometime now. The Briggs bushing are fairly thin walled so you might want to get a couple for each guide as they can get damage on install and have to be replaced.

That would be extremely helpful (and appreciated) to have those reamer sizes. Then I could provide that to the machine shop.
Michael

[KE4AVB]

9/32 IN INITIAL REAMER WITH 1/4 IN FINISH REAMER.

[creia]

Thank you very much KE4AVB. That information is very helpful and appreciated.
I will admit that I am still developing my skills with the "wiggle test" of a valve in the valve guide, and as such I am rethinking my "wiggle test" results. I just have not done this enough to know how much wiggle is too much , so I took some good precise measurements to share with you all and welcome your opinions...

Brand new Briggs 5HP exhaust valve STEM diameter = 0.245" to 0.246"
Exhaust valve GUIDE diameter on my 5Hp engine = 0.252"
That is a difference (tolerance) of 0.006" to 0.007"
Is that badly worn or is it acceptable?

Just for kicks, I also checked with the infamous Briggs "Plug Gauge" # 19122 that you insert into the valve guide to check for reject (Yes, I know they are basically useless!) and it will not even begin to insert into the valve guide and the diameter of it is 0.265"

After seeing the numbers I posted above can anybody tell me if my exhaust valve guide is still within specs? Worn out?
Thank you in advance,
Michael

[KE4AVB]

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.

[bgsengine]

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?

[KE4AVB]

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.

[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.

Yup. Another hint that may help "eyeball" it is - with vale installed and roll engine to open the valve, see if it wiggles enough that you can push valve to one side and roll engine some more and see if valve may "catch" off-kilter as it closes, if it operates smoothly and you can't get valve to catch enough to "hold open" it's probably also fine. (Again it's a judgement call as to how much is too much, but it is better than trying to measure to some precise value of go or no go - a badly worn valve face or one that is heavily carboned can catch much more easily than a freshly new or reground valve face will, so sometimes simply replacing or refacing valve will solve that issue)