Varnish build-up: How-to?

[Terry Caron]

May be terra incognito and the first time anyone's asked how to get some.  
My "new" McCoy .35 RH, crock-potted, has low compression after a run and topped out well under 10K w/10x5 wood Zinger and 6% nitro.
I've tapped the piston dome, slightly dishing it, to no avail.
I'm running 28% all-castor/0 nitro (my nitro mixes all have synth, and I've read as little as 3% prevents build-up) trying to build a varnish, but how best:
Sloppy 4s?
4 breaking  to 2?
Leanish 2 for heat?
Short lean 2s for more heat?

Thanks.

Terry

[Jim Kraft]

Most McCoy Red Heads do not have or will have the compression of a Fox 35 where they will hold it for a minute or so. If it pops when flipped as when starting it should run OK. As far as rpm on any prop I have no data. The funny thing about these engines is that they can have little compression and still put out the power of one with seemingly good compression. It just makes them harder to start. You can tap the piston again and lap it back in and it will probably be better, but you can break them also. I use Dupont #7 polishing compound for that with a little oil.

[Terry Caron]

Hi Jim -

It pops nicely enough cold, just basically runs 1K below my Fox Stunts.
I was expecting maybe 1K more.

In a earlier thread, Brett Buck suggested a varnish build-up was in order, and that made sense.
However, your comment brings to mind that reports are they were commonly lowish in compression and still ran well "back in the day".
When most if not all fuels were all-castor, if I'm not mistaken.
So maybe varnish isn't going to help.

Now I'm befuddled for sure.

I guess I need to try a love tap on the piston with a larger punch.

Update tomorrow, weather permitting.

Terry

[Terry Caron]

So, a few more taps on the piston didn't help.
I ran it with 10-6 APC/9N-63M-21C-8Synth and it tops out ~9100 rpm, 1700 less than the Foxes on the same fuel/prop.
I've also tried oven heating with no improvement.
I'll try the propane torch growing you've mentioned elsewhere Jim.

Terry

[Andrew Tinsley]

Hi Terry,
Most things you have done should work. It makes me wonder if you have either a head or crankcase gasket leak. Check your glowlug, I have known these leak through the fritt seal.

[Terry Caron]

Hi Terry,
Most things you have done should work. It makes me wonder if you have either a head or crankcase gasket leak. Check your glowlug, I have known these leak through the fritt seal.

Hi Andrew -
I've made new gaskets and tried 8-10 plugs, trying to find a hot one (I'm apparently out of 'em right now), but run characteristics remain the same.
And I don't see any leaks anywhere.
I don't know what proper specs should be but there's <.001" difference between cylinder/piston diam.
I need to dig out my mic and hole gauges to get exact measurements.

FWIW, I don't know if I'll ever put it on a plane, I'd just like to have a proper running McCoy RH for my engine accumulation, preferably the '57.

regards,

Terry

[Balsa Butcher]

Those sound like pretty good numbers to me. Those Foxes you are running are certainly stronger than the ones I have and MCoy 35's are seldom as strong as Fox 35's regardless. I think you have a good engine especially if it is only going on a shelf. If you want to varnish it up, put it on a Ringmaster and get some Powermaster GMA 10/29 (all castor). It won't take long. 

[Terry Caron]

Hi Pete -

Your words are music to my ears. 
Truth to tell, my expectations were based on comparing the old Chinn and Martin reviews of these engines (~10K Fox, ~11K McCoy, 10-6 prop).
They had new ones of course, but mine are all used so I expected generally comparative results.
So I'll just run it more, see if a build-up helps or be satisfied that it's at least normal. 

Thanks to all.

regards,

Terry

[Andrew Hathaway]

 

I tried Jim's methods on a junk McCoy 35, and promptly cracked the piston and broke the crankshaft.  Nothing wrong with Jim's methods, I just didn't have the finesse and respect for the job.  Shortly after I took the remaining bits and my other junk McCoy 35, and passed them off to Jim to see if a fair engine could be salvaged.  The result was a decent enough engine, it has enough compression to start and run reliably, but it's definitely not a Fox. 

[Brett Buck]

Hi Jim -

It pops nicely enough cold, just basically runs 1K below my Fox Stunts.
I was expecting maybe 1K more.

In a earlier thread, Brett Buck suggested a varnish build-up was in order, and that made sense.
However, your comment brings to mind that reports are they were commonly lowish in compression and still ran well "back in the day".
When most if not all fuels were all-castor, if I'm not mistaken.
So maybe varnish isn't going to help.

Now I'm befuddled for sure.

   I hope that wasn't because of anything I said. We are all speculating what, if anything, might be wrong with it.

   I wouldn't overlook the varnishing issue, There wasn't anything like synthetic model airplane oil  in regular use at the time, so it definitely varnished up, and I am pretty sure it has a sintered metal piston.

    But, as in the same thread on SSW, McCoy quality control was not even up to Fox standards, and they were known to vary from copy to copy. The Fox is wimpy compared to modern engines, but it was reasonably powerful comared to other engines at the time. It may really be  1000 rpm off a good Fox. So there may well be no problem at all.

  Break it in for a decent time with all-castor, then run it and see.

   Brett

 

[Terry Caron]

Brett - I wasn't dismissing your advice, far from it, and McCoy QC noted.
It just occurred to me that many posts have remarked on loose McCoys running ok (w/o particulars) and I was expecting more "ok".
(Glad it's not a Cub .29 OK!)  
More running is definitely in it's future; I enjoy that anyhoo.
(And I wasn't trying to hide from you on SSW - I know you're there too  ; some posters there don't post here. )

I confess, Andrew, I don't know how this piston has survived my ministrations.
I'd likely be excommunicated if any of you saw me "tapping" on it.
With a 12 oz hammer.
Did disappointingly little good though.

Terry

[Chris Wilson]

..... I'd just like to have a proper running McCoy RH for my engine accumulation,........
regards,

Terry

Possibly get the liner hard chrome plated and re- lap the piston back in.

This should outlast the lacquer from varnishing.

[Jim Kraft]

I have tried heat treating McCoy pistons with no luck. It may harden them but does not grow them any at least for me. I would sure try Bretts idea and run some all castor fuel through it for a while. I run several 35's and 40's, and I have some 40th anniversary Foxes that will out power them on the same fuel. The Red Heads do run better on profliles a lot of times because I think they vibrate less or just a different harmonic. A good one will 2-4 as good as anything out there. Brett is also right that they do have sintered iron pistons and it could actually be leaking through the metal itself. Like said above, put it on a Ringmaster or clone and fly it on good fuel and a 10-6 APC prop. Most of them seem to like a good prop load and may have more torque than the Foxes, just at a lower RPM. I run 12-6 APC props cut down to 10-1/2 yo 10-5/8 on my 40's to get more blade width, and they pull good. I just cut them off square and round the corners a bit. Of course, I am flying them on Magicians that weigh 35 to 38 ounces.

[Terry Caron]

I've thought about that Chris, and there's probably a shop around Nashville could do it.
I'm also thinking of delving into homebrew electro-nickeling, as much for funzies as anything.
Might not work/last long, but Hey! Who wouldn't like to electroplate at home?!!?  

In any case, for the time being I'm going with more running, as advised by so many.
Flying weather's coming, so I may even put in on the SterlingFlite RingStreakster, which flies well with a Fox.

Terry

[Brett Buck]

Possibly get the liner hard chrome plated and re- lap the piston back in.

This should outlast the lacquer from varnishing.

   This seems a little over-the-top for something that appears to be running more-or-less as expected. Even with a perfect fit will still be 4000+ rpm slower than current engines of comparable displacement.

   Brett

[Chris Wilson]

Hi Brett,

I suppose it depends on what value you place on an engine and how easily it to repair.

Here in Australia I could name three people off the top of my head who repair an engine that way or more likely make a new piston without thinking twice about it.

And by way of admission Terry has considered it also.

I
A chrome bore and re-lap would result in a better than original methinks.

Cheers.

[Andrew Hathaway]

A chrome bore and re-lap would result in a better than original methinks.

Cheers.

It'd be an improvement, but you'd still have a McCoy redhead with a soft piston and crankshaft, along with a handful of other shortcomings.  Chroming a McCoy might be worth it if a person were REALLY in love with that engine, but it's just perfume on a pig. 

[Brett Buck]

A chrome bore and re-lap would result in a better than original methinks.

  Perhaps - although I have seen so many messes created by people chroming things that I wouldn't rate the likelihood all that high.  But it does illustrate a problem I see all the time - the tendency to jump to massive modifications or perceived hop-up tricks, before even trying basic simple things like breaking it in fully.    We were beating on the piston with a big hammer a few posts ago.

This all on an engine that was once offered for $4 on a bubble pack card, and for all we can tell, is performing pretty much like it was intended +- the usual variation.
 
   Bear in mind I am just providing suggestions, as you are. They aren't commandments, anyone can do anything they want. But if you wanted something better than an original stock McCoy, I can think of A LOT better and more effective ways to spend your $100 or so.

   A far more effective method of improving the performance is our old pal, Vitamin N. It will blow in rather short order, but anything you do to get 33% more power will have the same result. Or we could have someone make a new crankshaft and conrod, too.

    Brett

[Andrew Hathaway]

The beauty of tenderly caressing the McCoy piston with a hammer is that at the very least all of us should already have a hammer, and a McCoy without a good piston is just a pile of junk parts.  It doesn't cost a thing, and after a little work you might end up with an engine that runs decent, and brings back a feeling of nostalgia, etc.  If it doesn't work, or you crack the piston, you've still got a pile of junk parts and the knowledge that at least you tried.  Or maybe I just enjoy striking precision machined ( ) McCoy parts with a hammer? 

Oh yes, we could chrome the sleeve, machine a new piston, put plastic pads on the ends of the wrist pin, bush the rod, commission a stronger steel precisely balanced crankshaft, with an actual mechanical link to the drive washer, and then a custom drive washer without raised pimples that damage props.  Ooh, we could hemi the head and stuffer the backplate, and drill - tap the top end for 6 full length grade 8 hardened head bolts.......  Or just start with a better engine and come out far ahead.

[Terry Caron]

Maybe getting a bit off-topic, as I still don't know if there's a "good" way to build varnish, but I'll say upfront that I don't intend to plate the piston.
It did cross my mind however, as I seemed to remember, rightly or wrongly, reading somewhere that someone (GMA?) plated some piston (McCoy?) for better performance.
And I can understand Chris' position of working with what you have as best you can.
I grew up in a "make do or do without" hobby environment and that approach influences me to this day.
Fact is, if I had to buy a $100 engine these days, it'd take a while.
So I greatly enjoy fiddling with the old engines I find, even if it's with bubble gum and bailing wire. 

Terry