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Old Oct 12, 2012, 01:55 PM
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We don't know the service was done incorrectly or failed to find an issue. Was it sent with a description of the noise, or was it simply sent for a bearing change?

Not running about the only thing that should make noise is the lifters on the cam. That noise will be pretty mild, just a click as you turn the crank over. If you rock the prop back and forth lightly you should feel just a bit of slop before the piston is moving in the cylinder. If there is a significant amount of slop, there could be a worn rod. I suppose a piston could be worn to the point it rattles, but this would be obvious when it was taken apart.

Glow engines that I purchase used always need bearing replacement.

Greg
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Old Oct 12, 2012, 07:53 PM
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United States, PA, Southampton
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Hey Guys,
Yes, I gave them a paper letter with the engine describing exactly what the problem was. I also expressed that they run it first to see for themselves and to run it when the work was completed to make sure it was fixed. When they recieved the engine they contacted me via email and I also emailed them about the problem. I also called twice to make sure the problem was getting fixed. I told the rep That the engine ran and that I only wanted the odd-knocking sound fixed. They emailed me and told me by phone they would run it and make sure it was running correctly before they shipped it back. They also sent the bearing back with it. They don't look nice but have good movement and no play so I really don't get the bearing replace. I will call Monday. I left one email with my concern but no response. I'm really disappointed with Hobby Servoces at this point.
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Old Oct 12, 2012, 07:58 PM
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I hope you get this sorted out.

Greg
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Old Oct 12, 2012, 09:45 PM
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What RPM is the engine making the knocking noise?

If it is only at idle, it could be end play in the crank causing the crank to "bump" out and in. This is very common on old bronze bearing motors but much less so on ball bearing motors.

Do you notice the knock when you let off the throttle at high rpm? This is usually the sign of a worn rod. Normally, you won't hear even a very worn connecting rod at full throttle since the piston keeps constant pressure on it. A really bad rod will knock at low idle due the flywheel effect of the prop pulling the crank between pulses.

Try to find out when, exactly, in the rpm range it is making the sound.

One last possible thing and this might be what it is. Check your MUFFLER. If the muffler is one of the newer cast designs that has some kind of a baffle in it this baffle can get loose and rattle around and make noise, especially in the lower rpm ranges. Higher oil content fuel like the 2nd kind you tried could help to mask the sound due to more or heavier oil coating the internals of the muffler.
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Old Oct 12, 2012, 10:13 PM
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Quote:
Originally Posted by Gooroo View Post
Normally, you won't hear even a very worn connecting rod at full throttle since the piston keeps constant pressure on it.
Not on an fourstroke....

Brgds, Bert
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Old Oct 12, 2012, 10:22 PM
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I don't think it is the rod.

In order for a model motor to have enough rod play to hear, the rod has to be very, very loose.

I generally have run many second hand motors with very worn parts, especially rods that have more than the expansion clearance play and I have never heard one.

In the automotive world, which is the 4 cycle world, you only hear mild rod knock when you let off the throttle. When the rod is very close to throwing you will hear it at idle and sometimes on the high end.

I am wondering if this guys motor has something other than the stock muffler on it or if it is a motor that came with a two piece muffler.

Most of the surpasses had one piece mufflers but you never know.
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Old Oct 13, 2012, 04:06 AM
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Quote:
Originally Posted by Gooroo View Post
Most of the surpasses had one piece mufflers but you never know.
Nope.... two part, screwed together with very fine thread, and probably lathed down to final finish after assembly.
I found out when I tried to make cooling fins in mine, and being almost finished doing so, suddenly cut into the thread....

But that should not be the cause of this problem (if there is any.... I wonder), because I never saw those mufflers come apart. Not even mine which runs uncooled and reaches close to 400 degrees C.

Some surpasses just have a slightly knocking sound, especially when they are being run at peak power with a heavy prop, and sometimes the plane they are bolted on, act as resonating body, amplifying this sound.

Brgds, bert
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Old Oct 13, 2012, 04:10 AM
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I just checked four of my mixed manufacturer's 4 cycles,and they ALL have a slight "click" on the cam overlap part of the rotation.

It is not a "Knock",just a light click......on mechanical valves,the clearance needed to run properly is always there.

If you have a second engine,see if it makes a comparable sound.
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Old Oct 14, 2012, 09:26 AM
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United States, PA, Southampton
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Hey Guys,
The knock is more intermittent than it is constant. It is on the high side. it actually got a little better from what Hobby Services did. So I'm guessing maybe it has to do with the rods or needs finer adjusting. I included some pics. Other four stroke 70's do not sound like this one. Thanks again guys for all you help.
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Old Oct 17, 2012, 07:08 AM
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Should I give Hobby Services a second chance?

I spoke to Hobby Services. After some back and forth they will look at it again. They kept saying it left here withing factory limits, but that is just not the case. I wish I had time to video the engine running. I explained I sent it up there with a certain problem and it was not addressed.
So should I give them a second chance or figure it out myself?
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Old Oct 17, 2012, 08:24 AM
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I'm guessing you have to pay shipping again??? I would make them figure it out. Just be sure they test run the engine and ask what fuel they are using. For that matter tell them what fuel you are using to see if it is comparable. If they don't find a smoking gun, when it gets back don't touch anything, mount the engine and run it. If it is still noisy, give them holy heck and demand a refund on at least the labor.... Maybe some shipping also.

Ken
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Old Oct 18, 2012, 10:48 AM
T.L.A.R. eng
Joined Nov 2005
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Quote:
Originally Posted by Gooroo View Post
What RPM is the engine making the knocking noise?

If it is only at idle, it could be end play in the crank causing the crank to "bump" out and in. This is very common on old bronze bearing motors but much less so on ball bearing motors.
Just a thought, my 80 4-stroke had a strange full throttle knock and I watched the crankshaft bounce in and out with the knocking noise. That engine didn't get run much either, and it turned out the dry cam lobes were causing enough friction to force the crank endplay by the timing gears.

Odd thing was, you could not feel end play, but you could see it with the engine running. Some lube on the cam lobes, problem solved.

A realatively large fuselage shape like a decathalon is a great amplifier for any noise the engine will make.
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Old Jan 21, 2013, 08:13 AM
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Hey Guys,

Well Hobby Services look at it again and adjusted timing. They also would not talk to me or return my emails. They shipped it back with the same problem. So I disassembled engine and found the exhaust valve to be sticking in less than an hour. That's the difference between a real Mechanic and Hobby Services I guess. Probably from sitting around for several years. Is you want something done right do it yourself.
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Old Jan 21, 2013, 02:15 PM
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I want a signature of the mechanic on the service ticket of every item that goes through a shop. The service tech should have no problem putting their signature on a document that associates them to a specific repair. If there is any question regarding that repair, ... the service tech can respond directly. When a diagnostic repair is made, .. that should cover all necessary repairs to that engine. If there is a cap limit on the cost, .. the tech can make the assessments and then notify the owner for approval.

A valve sticking is not just a simple oversight, ... it is on the lines of negligence. Especially when there is written documentation from the customer describing the type of problem here and a service tech who is employed full-time and specializes in this arena?.

The tech may have missed this on first glance, but when repair went to the bench for the bearings to be changed, .. I think he's into it far enough to go down to the valve-train for a thorough inspection? Especially on a four stroke engine with this customer complaint. Not to mention a formal discussion about this particular engine, ... online in this group. Did the engine even need the bearings, ... I doubt that it needed to be done. It seems that it needed a thorough cleaning and re-assembly? The customer says the bearings were smooth. If they were, .... maybe it would be worth the while to look deeper at the time of service? How hard would it be, for a qualified tech, to fix that problem and get that engine running to full perfomance on the first try? If not the very first try, ... at least by the time it was packaged and ready to ship back to the customer as a completed repair. Or maybe it's easier to just pretend to fix it and send it back, ... all at the customers' expense? Maybe the customer will be too ignorant to know the difference and they will just run it till it self-destructs?
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Old Jan 21, 2013, 04:05 PM
The Prez....... again
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United States, IA, Rockwell
Joined Jul 2011
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The tech probably squirted some WD-40 on the valve and hoped it would work / fix itself?????
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