The International Cessna 170 Association

Just interested to here if any of you have had any trouble with cracked inner coastals on your 170's with 180hp, with C/S prop without a dampener. I just bought a 170 and am having them check as I heard it can be a problem. I ordered a new 80" Hartzell C/S with a dampener to avoid trouble in the future. Any info would be nice. Thanks

The Lyc 180 (O-360) conversions do suffer a higher rate of cracking, of all types, due to vibration. This is especially noticeable during start-ups, as that 4-cylinder engine has a tendency to "shake, rattle and roll" during starts. Nosebowl, cowling, and windshields are especially prone, but other areas of the airframe also receive greater "pounding". It's generally thought that more horsepower crammed into fewer cylinders is the culprit . (The TCM IO-360, 6-cylinder conversion does not have this reputation.)

Although any reduction in vibration should be beneficial, I do not know if the dampened prop will be a "cure". If you go that route, be certain to have it dynamically balanced...not just statically balanced.

Help me here if you don't mind,I have been an A&P mec. since 1966 & I don't have a clue what an "inner coastal" is. I hope I know it by some other nomenclature.Since my 170B is equiped with a 180 hp Lyc & undamped Hartzell I would like to know exactly where to look (other than everywhere with this eng). Maybe a page,fig & index # from theIPC????

Hey Matt, welcome I don't know if you're a member or not regardless congrats on your new plane. As for the intercostals that you refer to, I believe you are referring to the angles that transfer the engine mount loads to the inside side of the stringers. Regardless of the engine installation, a good inspection here is well worth it, especially the rivets. Cracking in the skin in and about the engine mount is more likely around the bottom mounts due to fatigue combined with local corrosion. Are you using solid mounts or rubber mount to the firewall? Finally if you see Chris McCullock tell him Jim Mac finally convinced JDV to buy a real plane (170A)

I'll just comment for Zreyn, an intercostal is a general term given to an element of structure that provides a stiffening load path between structures as in a load path between stringers which transfer skin loads to Frames.

Thanx for that clarification,it seems to be stirring a slight fog of recolection now For Matt,I have always kept a sharp eye out for the cracks that the LYC conversion is "famous" for & so far after 1300 hrs. none of them have apeared. There were cracks at the bottom of the eng. cowel on both sides where it attaches to the fus when I got the airplane, Made repairs & have had no more cracks.(rubber mounts to the fus.)

Thanks to all for the response. I will be a full member very shortly, very good sight with obviously good support base. Thanks for the tip on balancing the prop, is that something that needs to be done at the factory or can a rebuild shop do that for you. I plan on installing a new O-360 next year and have it balance hoping that will reduce vibrations. As to answer what inner coastal are, c170b53 is right. They are located behind the dash were the engine mount comes though the firewall. My AME 's sag list on this last inspection found the top right inner coastal cracked with 1550 hours since 180hp conversion was done. About the mounts they were rubber but are being changed to solid for the STC for floats.

Prop shops traditionally "static" balance. This refers to balancing the prop on a stationary or "static" fixture.

The problem with static balancing is that blades are quite long and if one blade is 5-grams heavier than the other, and the prop is static balanced... that process only makes one side's total weight off-set the others. Once that blade is in-motion, the CG of each blade will only rarely be at the exact same point as it's opposite, therefore one blade will have a greater centrifugal force than the other, and further that force will vary in accordance to it's station (position or distance from the hub.) A statically balanced prop will beautifully balance across a fixture in the shop...but once it begins to rotate it may be quite out-of-balance.

Dynamic balancing the prop will not only take into consideration the forces of the prop while in-motion, ..... but will do so at the operating RPM closest to the cruising RPM as possible. AND...it will take into consideration any rotating out-of-balance vibrations produced by the engine-prop combination.

Few prop shops perform dynamic balancing, althought most shops can refer you to a local shop or individual who will perform the operation. Typical charges are $150-$250 depending upon local pricing, etc. but a fixed pitch, two-bladed prop should be priced at the lower-end of the scale.

In any case, dynamic balancing involves placing a transducer on your engine (temporarily bolting the device onto the engine nose-case area) and running the engine as near to cruising RPM as possible. The transducer will provide a signal to a laptop-computer-sized device which will identify the type, level, and order of vibration to the repairman. He will then place permanent weights (usually common washers) onto the back-plate of your spinner. The entire process is similar to balancing a car-wheel/tire combination except that a stroboscopic light and transducer is used in lieu of a balancing machine.

gahorn wrote: In any case, dynamic balancing involves placing a transducer on your engine (temporarily bolting the device onto the engine nose-case area) and running the engine as near to cruising RPM as possible.

With the standard prop the best you are going to get is about 2250 rpm which is below normal cruise power, but you will still see a great improvement.

Thanks for the info. I talk with Prop works in Edmonton Alberta were I ordered my new prop they do not dynamic balance props but they are looking into it for me. If anyone know of someone in the northwest, Alaska or in western Canada they could put me in contact with that would be great. Thanks

I have been flying our 0360 powered 170B with a Hartzell 80" w/dampener, for over 4 years now, with no problems and no cracking, other than the typical crack at the bottom corner of the cowl found in alot of the 170s and 172s. This crack, by the way was there in the cowl when we bought it with the C145 in it. Our prop has not needed to be balanced after purchase, and we have had no vibration problems with it. As George stated, the start up and shut down has more movement than the Continental, but the Lyc is smooth during normal running. It gets old hearing "wolf", especially from those with little actual experience, but alot depends how you fly and care for your aircraft. The dampener does its job well. It adds about 7 lbs I think, We balanced that with a B&C light weight starter, ( which really spins up the motor quick, thus eliminating some of the start up vibrations). PM me if you would like some more personal experience with that setup. Jon

Thanks, Jon. I talk to my AME again today. He said that the dampener is put on to stop this problem, that I new and thats why I bought it. My current 170 which is the second one I have owned there has been two inner coastal change and we are waiting for a new top left angel bracket that holds the firewall to the fuselage as it also has a crack. However the more I look into this airplane the less blame I put on possible vibrations and the more I put on poor piloting skills of the previous owners. MY AME said that he could dynamic balance the prop but said there is no need to with a dampener. Thank you very much for all the input. Did you have a 74" or 76" on your 170 before you put the 80" on and if so how much difference did you notice. Thanks sincerely Matt O'Brien

matt obrien wrote:... MY AME said that he could dynamic balance the prop but said there is no need to with a dampener. ...

This is not the same thing. If he doesn't understand the difference and does not think "there is a need"...then I suggest you find a different person to dynamically balance your propeller because the current guy doesn't ..."get it". (The cranshaft dampers and the prop balance...are different matters.)

O.K. I'm confused (don't know if it's again or still)are we talking about a vibration damper on the prop or on the engine that weigh's 7lbs?The only way to damp the vibration of an engine that I know about is with counter weights on the crankshaft,so I guess we are talking about somthing that you add to the prop that weighs 7 lbs???? Can anyone discribe this damper?

I'm excited about this, because I just had my Mac 1A170 dynamically balanced a couple weeks ago, after having flown it for 50 hrs since prop reconditioning by NW Propeller in Puyallup, WA. They static balance props going out the door, but the dynamic balance between the prop and the particular engine it is hung on, in my opinion, is a must-do.

My engine/prop combo wasn't that far out of balance (.38 IPS @ 2000 rpm and .44 IPS @ 2250 max static) but we got it down to .12 IPS @ 2000 rpm. It took 17 grams mounted to the spinner backing plate directly indexed with blade 1. My reasoning for paying $200 for even that amount of balancing is that the engine internals will benefit from it over the next 900-1000 hrs (currently 625 SMOH) and it's just more fun to fly behind. I already fixed a vibration issue by re-indexing the prop to the specified index position of blade 1 at 10:30. THAT was night and day. It's my understanding that prop indexing issues only plague older design engines like the C-145, is that true?

I read stories about some guys getting initial readings on the Chadwick in excess of 1.5 IPS. I imagine some owners never really know how out of balance they are, as our perspectives tend to drift over time. If I bought a new prop today, the first thing I would do is have it dynamically balanced, just as you would new car tires.

It seems like you could get a decently smooth running 4-cylinder engine if you had both the dampener and a good dynamic balance performed.