The International Cessna^® 170 Association

Thanks Bruce:

I'll spend some quality time with the logs and report back. And I appreciate the advice from all about not needing to pull the jug to fix the exhaust valve. Question - please bear with me if it's ignorant - is there value in pulling a cylinder to take a look at the bottom end on the engine since it's been 50+ years since major o/h?

Jim

blueldr wrote:... As far as changing the "Jesus" bolts is concerned, a 5000 hour airpane would have gone through 200 bolts in its lifetime. Seems like a hell of a lot of overkill to me.

One of us needs to check our math, Dick. I get 10 sets (20 bolts) on a 5000 hour airframe by changing them out every 500 hours.

jimnh20 wrote:Thanks all for the replies so far. I will get the main gear checked for alignment again, although I had that done and adjusted a few months ago. I have heard that the Pponk gear attachments need to be installed and adjusted correctly too or there can be steering issues- any comments on that?

The tail wheel geometry is positive castor, but I am suspicious that the linkage and springs are too loose. I plan to get the entire system checked out from rudder pedals to wheel. What tire pressure do ya'll keep in the tail wheel?

I want to get this fixed up so I can start joining everyone at 170 events

Regards

Jim

The P Ponk does not change the handling characteristics. all it does is add a reinforcement block on top of the gear leg at the attach point.

Jim, that is very reasonable. It also adds 70 lbs to the nose. Not worth the performance trade off.

Humm.. Actually it's 86 lbs if you try to mount both of them (blades 90 Deg apart) like the Ruskies do.
The weight difference is minimal.

Just because it's been 50 year in itself is not a reason to pull anything to look at the bottom end in my opinion. Now if you suspect there is bottom end issues it might be another story. As already been said you may be disappointed in what you can see if you do. What, other than time makes you want to look at the bottom end?

canav8 wrote:

jimnh20 wrote:Thanks all for the replies so far. I will get the main gear checked for alignment again, although I had that done and adjusted a few months ago. I have heard that the Pponk gear attachments need to be installed and adjusted correctly too or there can be steering issues- any comments on that?

The tail wheel geometry is positive castor, but I am suspicious that the linkage and springs are too loose. I plan to get the entire system checked out from rudder pedals to wheel. What tire pressure do ya'll keep in the tail wheel?

I want to get this fixed up so I can start joining everyone at 170 events

Regards

Jim

There is no room for adjustment when you actually see the pponk installation instructions, so no that is not true. Not sure what you mean by positive castor regarding tailwheel geometry. I asked you to post a picture regarding the geometry. It is alot easier to tel you what is wrong. As others have stated, there are threads with pictures showing what is correct and incorrect. D

There are four adjustments which may be influenced by the gear: Caster, Camber, Rake, and Toe-In/Out.

The P-ponk mod does not alter or affect the matter any more than the original mount does, so dis-regard what you "heard" regarding that matter. (The only thing I can think was possibly meant by that anecdote might be the lateral "levelling" of the aircraft using "shims" such as the factory recommended, common AN washers placed beneath the inboard-end of the upper gearleg)....and that should be addressed during any gearbox modifications. Any ordinary installation of P-ponk will not affect that matter.)

Rake is "set" by the gearleg and is not adjustable unless the gearleg is altered (not recommended.) Caster, Camber, and Toe-In/Out are all adjusted using the wedge-shaped shims placed between the axle and the lower gearleg.

ghostflyer wrote:Any mass when in a moving state has a certain amount of kinetic energy , to bring this mass to a stop it's best to spread the load (kinetic energy) over the greatest area as possible . If there is impeding stoppage , structures (P Plonk) that concentrate the load factors to a central point and the energy is absorbed in this area the most damage will occur in this area . If this area survives with the P Plonk fitted some of the other structure must absorbed the kinetic energy and the question has to be asked ,has it been designed to absorbed extra kinetic energy and has it deformed or failed . Energy can't be destroyed only changed in shape or form .....

That's an excellent observation.... and if you re-examine it, you will see that the original set-up concentrates all the stress on one little bolt-head...which, when it fails, can lead to destruction of the airplane....while the P-ponk spreads that stress over a larger area (their additional upper bracket) and MAY prevent the loss of the airplane.

Would I be wrong in thinking the majority of the gear load is transmitted through to the fuselage at the outboard gearbox bulkhead and thus the wedges and the bulkhead area should garner equal if not more scrunity than the inboard attach bolt ?

That is absolutely true, Jim.... unless the airplane gets out-of-hand and "hops"...such that there is an inward, sideload placed upon it so as to fold the wheel beneath the fuselage. Then the bolt head is the victim of that long-lever spring gear (the fulcrum being the blocks you are mentioning.) The P-ponk website has an excellent description and pics of the problem their "beef-up" kit addresses.

Jim...get the C/S if that's what it takes to get you out of the usual short haul missions and into the annual trek to the convention missions!

Miles,

No wonder my check book is so screwed up!

The only reasons that I never fited a CS prop on my airceaft when I fitted the O-360 was Cost, Extra weight and the C of G was too far forward and plus complexity of a CS prop. I have flown both types of aircraft [a fixed pitch /CS prop] ,while the CS is easier to fly ,I found the takeoff performances very similar. However all brands of fixed pitch props are not. I seemed to get more out of the Sensenich prop than the Mc Cauley . The Sensenich is a much better cruise prop. For climb ,they are both about the same. Both props were 60in pitch. One issue is that i have is due to the hollow crankshalf ,I have a RPM nogo zone of between 2250 and 2450 due to hymonics. I have learned to fly around this.
Last week it was 37 deg C and that really affected takeoff performance. Thats where a CS prop would have been helpfull. It was only me in the aircraft and half tanks.

I may have posted this in the past so please excuse me if I'm repeating myself. The differences in weight is very minimal, if there was a great difference as some attest, the Lycoming conversion would be a lawn dart.
The real difference (20 lbs.) in prop weight, (recouped in other areas) is the ARM of the weight which does make a difference. Having said that my aircraft operates within the C go G limits and I believe it would be difficult to get these conversions approved if they did not fall within limits.
A forward C of G is not a bad thing and seeing the I/O 360 with C/S in either a Hawk XP or a XP conversion (T.A., when it was available), is a manageable combination, I would think so would a 170 type with a Lycoming.
Yes, a valid argument about the differences in; battery size, location, components there and not there, engine weights, prop weights is valid, overall in the end you gain some and lose some, but the net increase in weight is minimal.
The climb performance cannot be compared as equal.
The RPM limitation is for some constant speed propellor/ engine combinations; does the STC specifically state a limitation when a fixed pitch is installed? Why would it apply to a fixed pitch ? I think if Harry was still with us, he would have a simple answer.

Bruce Fenstermacher wrote:Jim,

You really haven't told us much about this engine. What is it's recent history?

Sounds like you have some log book investigation to do. A 50 year old carb that is working has only one Ad to comply with that I can think of and that is the two piece venturi. And this is just a 100 hour inspection unless the venturi is loose. There were float and needle ADs which you need to review but I believe those all resolved themselves eventually that the original stuff was ok. But again you need to do do diligence and review your log history and the course of each AD. You can do this yourself and present a detailed history and findings to a mechanic and save him some time.

The mags will also need to have a log investigation. You did not say what mags you have. Makes a difference when it comes to ADs. The Scintilla (Bendix) SF6LN-12 have no ADs the much more popular Bendix S-20 series have a few and some that have come and gone. Certainly if no one has looked inside the mags since 1981 it is due.

Harnesses can be tested and leads replaced as necessary. You don't even have to remove the cylinder to fix a leaky exhaust valve if you find the right mechanic and intake hoses always look worse than they are.

The "recent" history as follows:

Engine total time 2075 hrs.
Mags overhauled 1981, 125 hours ago
Top overhaul 1969, 346 hours ago.
New rings and honed cylinders 1964, 615 hours ago
Major overhaul 1963, 707 hours ago
Compression checks - #5 generally lowest with April 2013 value 66/80.
Carb and Mag ADs appear to be complied with.

Jim

Generally other than calendar time since these overhauls, the time in service looks good.

So the question is how often and consistently has this engine been run? Has it been run a 1/2 hour every month since the top overhaul? If so the engine will be fine. If it was run 346 hrs from '69 to '74 and then sat since then the picture is much much different. If the engine sat for long periods, say a year, then operated fine for say a 100 hours and there was no ill effects then chances are good that period of inactivity had no ill effects. What causes ill effects is rust. If the engine did not accumulate any while inactive, it won't know the difference. If it does them when run the rust can wipe out cams, lifter bodies and cylinders first most likely and then perhaps at the same time the rust and wear metal it created circulating wipes the bearing and the crank.

These engines can stand periods of inactivity. And where and how it was stored makes a big difference.

So history, and recent history has to include the activity level or lack there of.

BTW two of my cylinders measured out at 66 over 80 this annual. One I couldn't tell where it was leaking the second through the exhaust. Probably both are exhaust leaks. I'm not planning to do a darn thing about it at this point. If I checked them today they are likely to be different and higher.

To answer Jims question, Sensenich does have RPM limits on the fixed pitch range as per there web page. I was between a rock and a hard place where i placed the battery as this effected the c of g range. It ended up on the fire wall due to accessability . it was a headache to put it in the tail.and putting lead weight on the tail wheel wasnt my cup of tea either.