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  #11  
Old 06-03-2021, 09:05 PM
BillL BillL is offline
 
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Location: Central IL
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For $90 it might be worth transplanting the camera to the 180deg head of the (my) VA400.

My Teslong borescope for .22 cal bores has excellent resolution.
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  #12  
Old 06-03-2021, 11:51 PM
mtnflyr mtnflyr is offline
 
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Location: Boulder, Colorado
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Quote:
Originally Posted by BillL View Post
For $90 it might be worth transplanting the camera to the 180deg head of the (my) VA400.

My Teslong borescope for .22 cal bores has excellent resolution.
I take it you arenít happy with the VA-400 resolution.
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  #13  
Old 06-03-2021, 11:52 PM
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Dan 57 Dan 57 is offline
 
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Looking at it now, Iíd also try the lapping.
The wobble test would be an indicator of the guideís condition, values published in SB388C, probably 0.30 for your engine. The SB also states If valve stem movement is in excess of the maximum limit listed in the table, the valve and guide must be replaced.
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  #14  
Old 06-04-2021, 12:19 AM
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rv8ch rv8ch is offline
 
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Quote:
Originally Posted by mtnflyr View Post
I take it you arenít happy with the VA-400 resolution.
The VA-400 resolution is much lower than the pictures shared above, but it articulates. Waiting to hear what Dan thinks of the VA-800...
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  #15  
Old 06-04-2021, 06:57 AM
664781 664781 is offline
 
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Default Pull Cylinder

With a compression test at 30/80 and running rough I would pull the cylinder!
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  #16  
Old 06-04-2021, 07:03 AM
BillL BillL is offline
 
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Default More is expected.

Quote:
Originally Posted by mtnflyr View Post
I take it you aren’t happy with the VA-400 resolution.
Clearly - - the mark-1's have been inspecting internal engine parts for 50 yrs and this just falls short of desired. Still quite useful, and the articulation is really needed, but since low cost CMOS with proper focal range is available at a reasonable cost it seems reasonable to expect more. Reasonable? Two much?

If Teslong made one that articulated, based on their other products I have seen, it would be 3-10X the resolution and same cost.

To the OP - as stated, wobble test is recommended - read the SB closely - likely .015 or greater is recommended. .030 is the limit (likely). You can spin the valve an get a better view of the seat with the valve sitting in the bore. If it looked nice and even there . . . Honestly, I would not lap until it had been checked and run for 5 hrs or so at cruise (not in the pattern). That's just me, and it's not that much time to de-cowl and get it back apart.

I recently helped TTHrew do a wobble test and hone, It was not difficult at all. There is a very good YT tutorial on the process that relocates the valve to the bottom of the cylinder then pulls it back into the guide, 15 seconds is all it took for that step. A strong magnet through the guide, good light, and snap-on two prong mechanical finger ($22). Do make a little hook from 0.040 safety wire to handle the valve through the upper plug hole an it can be viewed through the upper plug hole all the while. Following rocketbob's advice on the hone, it worked nicely.

Here is a David Clark short clip on his wobble fixture. YMMV but the valve did not exhibit a clear burning in some region, it looked even all around. Was the valve tight when you rotated it? Did you remove the the spring to make the video? Tell us more to determine if it is just a sticky valve with a tight guide.
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Last edited by BillL : 06-04-2021 at 07:20 AM.
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  #17  
Old 06-04-2021, 07:30 AM
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Dan 57 Dan 57 is offline
 
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Quote:
Did you remove the the spring to make the video?


Apologies for the thread drift:
VA-880 borescope Mickey... tested yesterday to inspect some tank installation on a T-51 Mustang project. Very happy, yet to test on an engine.
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  #18  
Old 06-04-2021, 10:33 AM
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Vividia quietly updated the VA-400 scope to a higher resolution - and also updated the price accordingly.
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  #19  
Old 06-04-2021, 11:01 AM
mtnflyr mtnflyr is offline
 
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Quote:
Originally Posted by BillL View Post
Here is a David Clark short clip on his wobble fixture. YMMV but the valve did not exhibit a clear burning in some region, it looked even all around. Was the valve tight when you rotated it? Did you remove the the spring to make the video? Tell us more to determine if it is just a sticky valve with a tight guide.
I did remove the valve spring to check the valve guide and push the valve in enough to get a good look at the seat. The valve moves freely in the guide with very little wobble. I'm making a wobble test fixture today and will measure that according to the Lycoming Service Bulletin 338C just to make sure I have a good guide.

Based on the responses, I'm planning to give the lap-in-place procedure a try. Seems like nothing to lose there and it just might fix the leak - at least temporarily. I'll post images of the result.

I have the custom exhaust valve guide reamer from McFarlane showing up today and plan on running that down the guide if the wobble test shows a tight clearance. They don't give those reamers away . . .

I haven't seen any comments on cleaning the base of the valve stem. That seems like the place where lead deposits would lead to a sticky valve. Since I'm messing around in there, I'd like to clean that part of the valve. Any recommendations on what to use? Purple Scotch-Brite?
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  #20  
Old 06-04-2021, 12:06 PM
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bruceh bruceh is offline
 
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I would keep any abrasive like Scotchbrite away from your engine! Mike Busch has a webinar on valve stickiness. He has some thoughts on the valve stem build up of crud and what can or cannot be done.
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