Hi Guys and Girls,

I finally have my C185A back off a rebuild after a wee "unscheduled off field landing" and she is a beautiful thing however..
It has a harshness (what my engineer calls it) I would say a vibration. We have tried most things and have reduced it some what but it's not the smooth machine it was before.

I have taken four other experienced 180/185 pilots and they have all found the vibration alarming.

The engine is first life and had 190hours at the time of the accident, it has been bulked stripped and reinstalled with a new Hartzell prop (had a black mac before)

It has many new parts, including a new "stock style" exhaust system, headers and muffler.

Very evident airborne on both mags (barely noticeable on the ground) The frequency is related to the RPM, it would be a low frequency (half order-ish?!), it become noticeable above 15inch of boost irrespective of airspeed, the higher the boost the more evident. The "yard stick" to give a fair comparison has been the A/H at first it was totally unusable, jumping up and down 10 degrees, now we have it down to a vibration the width of the bar.

So far we have;
ensured no engine parts are in contact with the airframe (some were and it has reduced the "harshness")
replaced the engine rubbers ( small improvement)
flow checked the injectors (perfect)
balanced the prop (dynamically) the results indicated the vibrations are originating from the engine.
Changed the prop to a black mac off another C185, harshness remained.

Thanks for any ideas or suggestions
Cheers Mit

Did prop strike ANYTHING on last "incident" water,short brush,trees etc ? Changing prop after its been running 15 or so hours can pick up vibration from bushings on counter balances attached to crankshaft. When you get engine overhauled is ONLY TIME to change prop as bushings are going to take a "set" while breaking in. I suspect prop hit something and needs teardown if problem continues .

Most the time vibration could be from a dead cylinder, incorrect mag timing. Sometimes when mag coils go out, the ground run will be fine and when it heats up then it acts up. I've also seen valve Clarence make them shake.

Sorry "Valve Clearance" dang auto correct

We had a similar issue with a T206. The vibration was somewhat noticeable on the ground, but became very pronounced at certain power settings. We checked everything you mentioned and then swapped props with one of our other aircraft and the problem vanished. We put the problem prop back on and balanced it, but the problem continued. We finally tore down then prop and found that when the prop was rebuilt, a new tech filled the hub with the incorrect amount of oil. It was off by only a few ounces, but it was just enough at certain power/RPM settings to make it vibrate. It took us a long time to figure it out, but it was totally smooth after that.

OH what fun! You have done everything that i would have. Soo many times it is one of the items you did.
Does it vibrate with the cowl off?
Does it vibrate just running on one mag or the other?
The firewall engine mount bolts are tight and structure behind ok?

Had one engine doing the same thing. Did all the same things you did to fix it. In the end the engine got tore down and nothing could be found wrong with it. That engine never got put back together, with lack of a smoking gun, and we installed a different engine. The new engine fixed the vibe.
Good luck

Had a similar thing twice in 206s. Muffler baffles had come loose and piled up at exit. Easy to check with a flashlight. But I think your system is going to be 6 into 1 instead of 3 into 2.

182 STOL driver wrote:Did prop strike ANYTHING on last "incident" water,short brush,trees etc ? Changing prop after its been running 15 or so hours can pick up vibration from bushings on counter balances attached to crankshaft. When you get engine overhauled is ONLY TIME to change prop as bushings are going to take a "set" while breaking in. I suspect prop hit something and needs teardown if problem continues .

Yes the last prop was totally buggered, the left main leg broke out causing a prop strike. It has a new prop.

PAMR MX wrote:OH what fun! You have done everything that i would have. Soo many times it is one of the items you did.
Does it vibrate with the cowl off?
Does it vibrate just running on one mag or the other?
The firewall engine mount bolts are tight and structure behind ok?

Yes it does vibrate with the cowls off, it is hard to feel on the ground, but the dynamic balance showed it up clear as a bell.
It does run ever so slightly better on one mag, but still evident on either
Yes the bolts are tight, and the fire wall as been rebuilt.

elgoatropo wrote:Had a similar thing twice in 206s. Muffler baffles had come loose and piled up at exit. Easy to check with a flashlight. But I think your system is going to be 6 into 1 instead of 3 into 2.

I will check today.

Thanks so far, I will mention all this to my engineer. it could be in the valves

I should add that when we balanced our prop the vibration stopped but every time we went flying the vibration came back. The oil would accumulate on one side and make the vibration come back. Additionally we have recently had issues with the internal timing in the mags slipping. They have been significantly off after a few flights. Due to this they also run slightly better on one mag.

Good luck, please let us know what you find.

Hey Mit,

I'm glad to hear you are flying again. Did you get the new pod on yet?

As far as your vibe goes, once we traced a nasty vibe to mismatched pistons. Somehow or another during a top overhaul, a heavier or lighter piston go,t installed so the nice original balanced set was no longer complete. It is no fun to have to go that deep chasing a problem, but it may come to that.

Tony

AEROPOD wrote:Hey Mit,

I'm glad to hear you are flying again. Did you get the new pod on yet?

As far as your vibe goes, once we traced a nasty vibe to mismatched pistons. Somehow or another during a top overhaul, a heavier or lighter piston go,t installed so the nice original balanced set was no longer complete. It is no fun to have to go that deep chasing a problem, but it may come to that.

Tony

Hay Tony,

Yes, I have been meaning to email you, it went on a dream! With the nice straight fuse skins we barely had to grind anything off it to get a perfect fit. Also figured out a way to speed up the process of fitting (which I'm sure you are on too..) but I won't bored everyone with here, I'll send an email with a few piccys.

As for the engine, I am still holding out hope that it won't have to come to pistons, we did have a small improvement today after finding another contact point which has shown up in the paint work with more flying. Will rebalanced the prop tomorrow and see how we are going (balance weights were removed)

We also did a leak down and they were all very even, the front left cylinder (no.6) and left middle cylinder (no. 4) plugs were blacker than the others however we had idled for a long period after the previous flight, and comparing the plugs to the other C185 in the hanger, the plug were similarly colored.

Cheers Mit

Hey Mit!

Not sure whether you'd remember meeting me at the hanger in PM?

Been interesting watching Neil restore your machine over the last few months, glad to hear it's come together. The new paint was looking great last I was over there.

Sorry to hear about the vibration issue.... Hopefully something benign like cowl interference. It sounds like it's not a resonant vibration at certain frequencies, but rather an engine issue that happens at all frequencies over about 30-40% power?
Is it worse at full power?
Do you have full multipoint EGT / CHT gauges installed?

Jonathan

When you dynamically balance the prop, did you check IPS/ vibration levels on both ends of the engine? Most techs will only attach the velocity probe to the front of the engine, if there is an internal engine balance issue it’s possible to increase or decrease the vibration level at the rear of the engine by changing balance on the prop. Good luck.

On secong thought, do you have EGT and CHT on your engine? It sounds like your loosing power on one or more Cyl. an engine analizer may help you sort this out.

Did you check the injectors on the bench or from the fuel distributor on the engine?
A friend of mine had a large Continental that had a similar vibration, it turned out to be a replacement fuel line running to an injector, although the injectors all flowed the same, the fuel lines did not. Also check the engine mount bolts to the fire wall, make sure that they did not shoulder out on the bolt leaving the mount loose to the firewall. Good luck.

I assume the rebuild included new counterweight pins, bushings, etc. A problem there will cause vibration. A counterweight problem ended up breaking the crankshaft in one of the old man's Navions (GO-435 I think) - not a good thing. But it is not an easy thing to check.

I have a friend that had a very similar condition. They were pulling their hair out trying to find the problem. I suggested they do a compression test. They said they had done a leak down test and all was good . I said , no I mean an actual compression test. They thought I was nuts but they humored me. All the compressions were the same except one and it was 15 lbs higher. Seems someone had accidently put a high compression piston in one hole. The same outfit did not gap the rings properly on any pistons and actually installed a number of rings upside down. My buddy paid $22k to have his o-235 rebuilt by this clown.
Did you check your compressions today?

I like your post, leak down V/S comp. test, good point.

Double check (like anally) all the tubes of your engine mount. We had a 185 that had a sort of mild but new vibration. Turned out there was a broken tube in one of the lower engine mount legs.....and it was next to impossible to see....paint and location hid it. Smart mechanic Found it by uncowling and gently lifting on engine.

Spooked me, cause I'd flown that thing several times recently.

MTV

Is the prop clocked right?
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