Stuck valves

[Tom Downey]

Tom, BTW, the tools you posted a link to (.354 & .375 hones) are both the wrong size for the C145 exh guide.
Eric

Correct Eric, I linked them because I could not get the proper size to pop up. But the style is what I use in setting final clearance to new guides.

and they do a great job in cleaning the lead out of a guide as in stuck valve.

[n3833v]

This place might help in finding a reamer.

http://www.mcmaster.com/

John Hess

[GAHorn]

If you use that link, use it's search routine with the word "reamer". McMaster-Carr is a well-respected supplier (although not cheap.)

The best method of reaming a valve guide is with the cylinder off the engine to avoid metal chips from entering the cylinder where they can injure the piston/ring/cylinder wall and where they can work their way between a valve and it's seat causing burning.
Use a differential compression tester to run low pressure air into the cylinder while reaming to keep the chips blown out the valve guide rather than fall into the cylinder. (And wear eye protection.)

[N2540V]

This starts out as an interesting article.
Would somebody who has a subscription give us a summary and the application (and cost) to our engines?
http://www.aviation-consumer.com/pub/35 ... 482-1.html

Thank you,
Jim

[GAHorn]

Porting and polishing is commonly done on race-car engines. The theory is that smoothing the flow, and reducing "back pressures" or "intake resistance" by polishing and straightening out the flow patterns of intakes and exhausts is beneficial to obtaining maximum horsepower/performance.
The problem with doing this to aircraft engines, in my opinion, is that our cylinders are made of steel barrels threaded into aluminum heads with a certain amount of mass to them which defends against cracking. If ever you've had to do a cylinder repair/top-overhaul and been shown and told your cylinder is condemned due to cracking...and seen that the very place they crack is in the area of these valve ports...you'll likely see the merit of not reducing the wall-thickness of the ports. Thinner walls will be less capable of absorbing and dissipating heat and will be more likely to suffer cracks.
Then there's the OEM or original manufacturer of the engines opinion, which historically has been that such modifications are unnecessary and marginalizes the engine. The engine as originally designed and certificated meets the horsepower and performance certification and documentation of the airframe/engine combination. Such additional monies are monies well squandered for such minimal gains and reduced reliability.
This reminds me of the "designer engines" syndrome that some shops offer. For regular price, you can buy the officially certified and approved overhaul for your engine which meets all the mfr and FAA requirements and expectations. But for more money you can get one painted RED or GOLD or GLOSS-BLACK and they'll be SUPER-engines. Yeah. Sure. You see 'em most frequently on doctor/lawyer Bonanzas.
"...vanity and all the crimes it leads to..." (Can you spell "sucker"?)
My two cents wasted?

[cessna170bdriver]

Sorry Jim (N2540V),

I should have warned you to get out your fire suit! When it comes to most mods, George is always standing by with his torch. (Just kidding George!)

FYI, Lycon (Visalia, CA) added an unsolicited quote of $1350 "To Port polish and Flow balance cylinders and induction" to a recent overhaul quote on my O-300A. That is more than the difference between overhauled and factory new cylinders ($1176).

I don't know the validity of it, but I have heard that the roughness in the induction system aids fuel atomization.

Miles

[GAHorn]

You're not kidding, Miles. You're being factual.
Actually, there are quite a few mods I'm a fan of. Pponk gearbox beef-up, B.A.S. tailpull handles, upgrade to solid alum or steel axles, Cleveland brakes, shoulder harnesses, dual venturiis, ...

[zero.one.victor]

I don't know the validity of it, but I have heard that the roughness in the induction system aids fuel atomization.

Miles

A friend of mine was having fits with a rough-running freshly-OH'd O-200 from an overhaul shop,for which he had traded in his old run-out . He de-gauzed what appeared to be magnetized lifters, replaced the apparently out-of-spec cam, tried different mags, and a whole buncha other stuff. After all this did not improve things, he was talking to a TCM factory rep (George's friend Cory) who suggested that he might try replacing the induction spider. The one he pulled off was smooth as a baby's butt inside, while the replacement was rough as a cobb. Loe and behold, that seemed to do the trick. Same deal, we figured the rough flow surfaces helped atomize the fuel/air mixture.

Eric

[cessna170bdriver]

You're not kidding, Miles. You're being factual.
Actually, there are quite a few mods I'm a fan of. Pponk gearbox beef-up, B.A.S. tailpull handles, upgrade to solid alum or steel axles, Cleveland brakes, shoulder harnesses, dual venturiis, ...

Well George, at least I did say MOST mods. BTW, dual venturis is a mod? They show up in my IPC (B-model). Maybe it's just semantics; mods vs. options?

Miles

[GAHorn]

For YOU, Miles....(with the way your poor airplane has been confused) .... it would be a mod...back to original.
For the rest of us,...it would be the factory IFR option.

[cessna170bdriver]

For YOU, Miles....(with the way your poor airplane has been confused) .... it would be a mod...back to original.

Not so George. '98C has had dual venturi's since very early in its existence. As long as the SVSIII knob is pushed in, which is 99% of the time, the dual venturis do all the sucking. Remember, the SVS is a BACKUP system.

[GAHorn]

My profound apologies. I thought you had a O-300-D and vacuum pump with a backup system. I don't know who I'm thinking of now.
Dual venturies are a good, adequate system and shouldn't require any backup, in my opinion.
Best regards
George

[Dougie]

Well I got my first stuck valve in my O-300 about a week ago. I grounded my plane until I can repair it with the rope trick.
I bought new springs, because the logs show the cylinders were inspected and returned to service at the last top overhaul. No mention of spring replacement (I suspect old and weak springs). My question is, when I clean the valve guide out everyone is reaming with a .4375" ream. Would emery cloth on a wooden dowel be acceptable to clean the guide, I tried it on an old cylinder found at the airport and it worked at cleaning the carbon deposits. I just wonder why this method has not been mentioned, and should I or should I not do it this way.

[GAHorn]

It should work,... if you don't mind abrasive residue in the cylinder, but you'll not have an accurately sized valve guide unless you use a reamer, of course.
I have cleaned valve guides while the piston was BDC and while introducing a few lbs of air thru the spark plug hole to keep as much residue as possible out of the cylinder. I used my compression tester to do the work. (It was on a J-5 Cub with a C-90 engine... for those who have a good memory.)

[Bruce Fenstermacher]

Dougie

In past threads I described a scraper I have used to clean about 10 valve guides to date. It is nothing more that a 5/16" od. piece of soft copper plumbing pipe (I think it is 5/16". It need to fit in the valve guide.)

I use a utility knife to sharpen the inside of one end and it would hurt to use a flaring tool to put a slight flare on the end.

Any my thoughts are that your valve guide is or was the right size. You just want to remove the carbon build up not any guide material. Of course the correct size reamer would do this as well but the reamer could remove guide material. Of course if you find after cleaning the valve and the guide that the fit is tight it's time to get the right reamer.

George's suggestion about the positive pressure in the cylinder is a good one. I blew out the cylinder if I had air after the procedure but a few of the valves where done in the field with no air available. In this case I wasn't to worried about the carbon that was left in the cylinder but I would be had I used a reamer which could have removed guide material along with the carbon.

There are probably a half dozen tools and techniques that can be used and all accomplish nearly the same thing. I would be sure to read the old threads on this subject specially the warnings about removing the push rod and the damage that can occur depending on the hydraulic units you have. Don't turn a relatively simple problem into a mess.

BTW I gave a demonstration on "the rope trick" and displayed the tools I use and others I gathered for show and tell at our last convention. Just one thing you might see and another reason to join TIC170A and attend a convention.

One last thought. You would usually want the right tool for the job and that usually comes with a price. Rarely do cheap tools work well. I've not found this to be the case here. The last reamer a friend bought he thought he got cheap at $50. My piece of copper pipe came from my scrap box but wouldn't cost more that $2 if bought new.