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There are several threads proposing that the correct reamer for a 1/2” exhaust valve is the McFarland VGR-LC4. I suspect the better choice is the -LC3. My valve stem measures at 0.495 or slightly less depending on location and technique. According to the McFarland chart the LC3 is the better choice with a maximum cut of 0.499. Slightly undersizing the guide. It seems safer to slightly undercut at 0.4995 rather than overcut at 0.5005 as the LC4 does.
I believe 0.4995 which would be the size of the LC3. I can’t find the Lycoming reference I used.
This is good to know as most people seem to be using the LC4. Thanks for your info, I will do a bit of research to see if I can find any info. Perhaps a call to Lycoming to confirm the reamer size would be good.
Even using an electronic caliper, whether calibrated or standardized...you will get a much more accurate measurement on a reamer by measuring it with a 0-1" Micrometer, regardless of type or style. Most Digital Mic's today are capable of easily measuring down to .0001 increments, which is closer than we need to worry about.
The picture below is from SSP1775-5. I propose the min number of .4995 (LC3) as the better option, so long as the post procedure wobble check is within limits. If the guide continues to build deposits the process can be repeated. If the guide continues to wear, over time using the max (.5005) may reduce time before guide replacement.
Marvin,
Bavafa,
Thanks for the additional info. I also checked the reference guide, page 18, and looks like based on that the LC4 is the correct reamer size. I also understand and appreciate your approach here.
No I use 320 grit.
Ball hones are cheap and easy to find. No risk of cutting way guide material
Thanks. No fault with your logic here. A pilotted reamer is a great thing to help mitigate risks when reaming and much safer than a non pilotted version. However, a ball hone doesn't carry those risks, so no need for a pilot or guide. You just run it through a few times until you see the black turn to a metal color. Even if you go too far, a 320 grit hone just can't remove much material; It is designed for surface finishing and NOT surface removal. Think 320 grit sandpaper vs drill bit. A reamer on the other hand is a CUTTING tool. If not cautious, you can take away material you don't want to. IMHO, a ball hone is a FAR safer way to remove debris from the guide for an amateur.
Don't know if you know this but valve guides wear on one side of the guide and on the opposite side on the other. The rocker puts a side load on the valve in operation. The reamer will not clean up these areas and will leave carbon build up depending on how worn the guide is. The pilot does exactly nothing in this case. Ball hone will leave a crosshatch finish and conforms to the wear areas. I have never had a valve stick after using the ball hone to clean the guide. Its a better suited tool for the task and are inexpensive.
Bob,
The pilot starts on the end which is not round, therefore it's impossible for it to ream straight.
ok. good luck
Now that we know the tool, how about a short tutorial on how to use it? Any guide/insight on what speed the drill should run? Is there any chance of mishap if the hon's end exists from the other side of the guide inside the cylinder? I have never used a hone but interested to learn and may use it next time I need to clean the guides? I used the McFarlan's reamer and it was pretty straight forward, not so much pulling the valve back into the guide.
if no symptoms are present, I would perform the wobble test (moderately precise estimation of clearance) over complete disassembly and visual inspection (highly imprecise, unless using Micrometers and hole gauges). you can use the results to track progression as well as make decisions about remediation.
You see, this was a great tutorial and I thank you for that. I am going to save this guide as it will one day become handy.
How does the carbon build up get removed out of the piston?
Are you refering to what might fall into the cylinder? If so, nothing to worry about. While a reamer will take out chunks, the ball hone produces something like dust. Think byproduct of sanding or grinding vs drill bit shavings. It won't hurt anything in the cylinder. A ball hone uses an abrasion process.
Yup, fat fingers, not enough coffee. I do mean what may fall into the cylinder.
