Losing compression on my Tee Dee .051

**RknRusty** Sun Aug 25, 2013 9:13 pm

This is the Tee Dee .051 on my BFS-I, now my Cox contest engine. It used to have an impressive pop when flipping the prop over TDC. This engine I believe probably grew up on pure castor fuel, but I bought it used, so I can't be 100% sure. I always ran it on Glowplugboy pure castor. It continued to maintain good compression. Since Mike McGraw, Glowplugboy passed away, I've been using Sig, which of course is half synthetic/half castor. Recently I have noticed lower compression. I even changed to the new drop=in plug and clamp that Bernie sells. That setup usually requires extra washers, but I'm down to 2(IIRC) washers and still don't have that strong pop over. On the first start, it was even hard to crank today. Unusual for that engine. Once it was running, I cannot tell there is any performance dropoff. It's still a mean running engine. What are the odds the synthetic has washed too much varnish off of my cylinder wall?

I have read that on Fox engines, if it's been run primarily on castor all its life, castor/synth blend will kill its compression. I fear that's what happened here. If I buy a new P/C and break it in on Sig, I wonder if it will be shorter lived than if I buy pure castor fuel for it. If I can't find a NIP Tee Dee .051 P/C, I'll have to get one of Bernie's .049 sets. That is not what I want. As I write this, it occurs to me that I haven't tried another head since I noticed this, so I'll try a swap before I take any rash action.

pkrankow Sun Aug 25, 2013 9:27 pm

Ordering new fuel is not rash action. It will take a quart or so to build up varnish again if it really is the varnish loss.

Phil

**Cribbs74** Sun Aug 25, 2013 9:39 pm

No real way of telling. It could be varnish loss, but if that was the case it was worn from the get go. A few lean runs can also cause this as I am sure you are already aware. If it still runs well then don't worry about it. The p/c set in my unlimited engine never had much of a pop right from the start and when hot there was almost no compression at all.

The more I mess with these things the more I realize how quirky they are.

Ron

kevbo Sun Aug 25, 2013 9:43 pm

Hey rusty!

If it starts I don't worry much over how the compression feels. At full chat the pressure has only milliseconds to bleed off. Burt Goldsmith has a Norvel that feels like the head is off when you just turn it, but that sucker starts (well, eventually, i confess) and runs very strong...scary strong I would even say. Close fit feels nice, and may start easier, but a little looser can have less drag.

It seems wrong to me that you are removing shims to get the right feel when starting. I use a tach and shim for best RPM and maybe one less shim for airborne unloading. The shims and nitro set ignition advance, if too much you get less power and more heat. Also can make starting harder, as it is more likely to kick back, but TD won't run backward like a reedy, so it just seems fussy.

**RknRusty** Sun Aug 25, 2013 9:52 pm

Thanks for the reassurance, guys. A Tee Dee P/C(especially an .051) is a terrible thing to waste.

tru168 Sun Aug 25, 2013 11:11 pm

Hi Rusty,

My new Sure Start variant engine broken-in using 0% nitro, and 22% pure castor for about 30 minutes total . P/C will hold its compression virtually forever. I turn it to TDC and after few minutes , I turn its prop and still can feel strong kick.

After that I run a few tanks of 10% Sig Champion fuel, it can't hold its compression anymore,
I hold the prop and let the gravity to turn and drop the cylinder, thats means , the compression seems real weak, that the weight of itself can turn it over TDC in a few second!
It starts a little harder now , but once it start running, its RPM seems not much different, I cleaned the P/C in ethanol spirit, oil it and I ran it in my homebrew 78% methanol + 22% castor, after a few tanks , the compression seems back to normal, and RPM remains the same.

Looks like some fuel will remove its varnish to keep engine clean.
I have one # 290 production engine which had been used nearly 15 years, and its compression really low, Some of my clubmate even say it will not start and I need to replace a new P/C set. I always start it using small electric starter , (with copper drive plate ) and its a real screamer !

Ken Cook Mon Aug 26, 2013 6:50 am

I certainly would begin with new head shims. I would then flatten the glow plug on a piece of glass using some 400-600 wet dry paper and some oil. If your using the 1702 high comp head, there is a small ridge on the mating surface of the bottom of that plug. I would lap the plug on the paper until the ridge is completely gone. More times than you can imagine, the head shims can very well be responsible for this problem your experiencing. The head shims are really only good ONE time. We all use them over and over, but they work harden after the first compression of tightening them. After that they've been compressed which leads to the plug coming loose repeatedly and loss of compression. I would also lap the back of the case so that the back plate mates nice and flat.

You really don't want varnish in the cylinder. Varnishing is not helpful to assisting your engine run. It may induce compression, but it's going to decrease performance. I have many engines that run and do it quite well with very little compression. Using a Davis Diesel cylinder brush can also restore some life into a tired cylinder. I wouldn't dismiss the piston/cylinder until you've tried the above. Ken

tru168 Mon Aug 26, 2013 7:06 am

Yea, Thanks Ken reminds me about the head shim too.
Sure Varnish is bad for cylinder, mine looks a thin layer of thick castor coated in it.
I read mouse race modification on black widow somewhere, and mentioned that the piston and cylinder will be in optimum fit when a tap on it, the piston will drop from its TDC, I bet that engine will not feel much compression either, but will perform well due to its low friction loss.

SuperDave Mon Aug 26, 2013 9:21 am

Rusty:

This may seem obvious but are you running a high-compression glo head which is standard equipment on TD .049-.051's? A standard head will not give you the compression typical of these engines.

SD

**RknRusty** Mon Aug 26, 2013 10:50 am

SuperDave wrote:Rusty:

This may seem obvious but are you running a high-compression glo head which is standard equipment on TD .049-.051's? A standard head will not give you the compression typical of these engines.

SD

RknRusty wrote:...I even changed to the new drop-in plug and clamp that Bernie sells. That setup usually requires extra washers, but I'm down to 2(IIRC) washers and still don't have that strong pop over...

Thanks for the replies. First thing I'll do is check the head seat. I actually did use new gaskets in this one. I'll put the old 1702 back on it just to compare how it flips over. I replaced it a couple of months ago because the glow element was weak.

SuperDave Mon Aug 26, 2013 12:16 pm

Rusty:

TD .049-.051's will run with standard head but there performance will be rather anemic compared to a high compression head.

A "weak" glow head usually is the sign of weak battery, a faulty connection or dirty glo element. (I'm sure that you are aware of these factors) Double check them again to be sure.

SD

**RknRusty** Mon Aug 26, 2013 1:22 pm

Thanks, SD.

gcb Mon Aug 26, 2013 7:26 pm

Opinions:

Years ago before folks used synthetics in Cox engines the all-castor fuel would varnish up an engine if it was run hard and lean. When power dropped off a bit, we would clean the cylinder with Hoppe's gun cleaner, a Brillo pad (wet), Scotch-Brite or some other equivalent. A few mixed Hoppe's with some fuel and ran a tank or two to clean it out.

Some synthetic in the fuel prevents that. If the fit is a bit loose running all-castor may increase compression a bit. As someone mentioned though it's not the fits when cold but when up to operating temperature that count.

George

**RknRusty** Mon Aug 26, 2013 8:02 pm

I think that's it in a nutshell, George.

I'm going to toss it in the car so I can give it another rip tomorrow when I go out for my Shoestring practice. It helps me relax to take a 1/2A break in between concentrating on Pattern flights. Is that weird? I guess it gets me back in my comfort zone a little.

When I do all the post flight cleaning, I'll take a close look at the Tee Dee and see what I think about it. I've been known to worry much about nothing in the past, so maybe this is just that again. It also occurred to me that the difficulty cranking on the first flight Sunday, was that I had possibly put too much air tool oil in it. And it's not completely devoid of compression, just not that old pleasing pop I'm used to.

I'll file a flight report tomorrow. We're hitting the field about 9:30 AM.

Rusty

SuperDave Tue Aug 27, 2013 9:38 am

Yea Hoppe's #9 Geo!

Why make cleaning difficult?

SD

balogh Thu Aug 29, 2013 9:41 am

Guys,

2 rules of thumb I have always followed and thus managed to have very strong compression even after 50 hrs run on COX engines:

1. always have at least 22% castor - and castor only - as lube in the fuel
2. Do not let the engine lean out on fuel-air mix. This can kill compression really quick, but if you accept her run on, say, a '/4 turn of the needle extra over the peak rpm (small compromise on the rpm), even when the level in tank is low and fuel supply diminishes, there will be enough draft of fuel through the needle valve to avoid leaning out.

SuperDave Thu Aug 29, 2013 10:29 am

Balogh:

Agreed.

Lauching at "full scream RPM" has never worked well for me either. That may not apply to "pressure fed" engines.

SD

tru168 Thu Aug 29, 2013 10:37 am

Hmm...... Don't know how's Rusty's Tee Dee run . any update Rusty?

**RknRusty** Thu Aug 29, 2013 11:42 am

tru168 wrote:Hmm...... Don't know how's Rusty's Tee Dee run . any update Rusty?

Yes, actually. I took her out for a quick rip yesterday and cranked on the first couple of flips. I might have over filled it with after run oil causing the troublesome first crank last week. It is lower on compression than it used to be but I can't tell any performance loss.

As for Balogh's mention of launching rich, I usually turn it back off peak until I hear the first crackles, but not a full stumble. After the first full lap, or sometimes two, it unloads into a full scream. Probably not the best idea for preservation, but my flying style needs the whole thing. I'm going to start adding another 2% oil to all of my fuel. I think that's a good idea. Certainly can't hurt.

tru168 Sat Aug 31, 2013 9:33 am

Glad to hear it maintains its performance！

Sponsored content

Losing compression on my Tee Dee .051

Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051

Re: Losing compression on my Tee Dee .051