RCV58CD

[Manish Chandrayan]

IMHO, It's a four stroke, therefore for the cylinder to make one full rotation, the crank (and the piston) makes four. If the sound was due to bent shaft or connecting rod it would be heard during each rotation of the crank.  

Have you lent an ear to the demo video of the 58 CD? Does it not sound similar to what Andy is experiencing.

As I said earlier, I had the same sound and it went away once the engine was hot enough (running) and would return once the engine cooled down. Therefore my bet is on the torque applied to the 6 case bolts causing this 

[Andy J]

Removed the engine and again split off the lower casing. Removed the con-rod and could not observe any misalignment in the two holes but did note that there was some wear on the gudgeon pin where it interfaces with the cylinder at both ends.   Lower end of the con-rod is not a good fit to the crank pin and can be moved ever so slightly so there is obviously some wear there.  No obvious damage to the gears or rotating cylinder wall. Crank pin appears to have no damage.

 

Re-assembled the engine with the con-rod in what was believed to be the correct orientation and noted that it was free to float backwards about 1 or 2mm. Put on the lower case and the noise returned when the engine was turned over.

 

Re-split the engine and turned the crank 180 deg as in my original picture. Noted that there is then no play rewards in the conrod as it sits against one side of the cylinder.  Bottom case put on and ........ no noise!

 

 

 

[Manish Chandrayan]

Have you hit upon the magical solution? 

 

[Andy J]

Spoke too soon as to finding the issue! Was just re-installing the engine back in the model when I noted a copper thrust washer sitting on the bench which looked very like the thin washer that sits between the crank pin and the con-rod.  Engine therefore removed and again split open. Washer fitted and the lower casing re-fitted.

 

Result was that the noise has returned so open as to why the washer and con-rod position causes the issue.

[Martin Harris - Moderator]

17 hours ago, Manish Chandrayan said:

Have you lent an ear to the demo video of the 58 CD? Does it not sound similar to what Andy is experiencing.

 

Might that be the reason that particular engine was selected to be sectioned!  ?   ...or something to do with the ring catching on the cutaway in the cylinder?

 

Did you check the piston and bore for any scuffing/pick up evidence or try oiling the piston through the inlet port?  If you can face another stripdown/rebuild or two (it should hold no terrors by now!) you could eliminate the piston as the cause by assembling it minus con rod and piston - play with the case screws to see if you can recreate the noise and thereby prove or eliminate any gear mesh misalignment.

 

P.S. A very small clearance is normal in a big end bush and allows an oil film to be formed.How much is too much?  Maybe Jon could comment on what is acceptable and how to measure it but I suspect assessment is down to experience and "feel".

Edited May 15, 2021 by Martin Harris - Moderator
P.S. added

[Manish Chandrayan]

Surprised hearing about that washer being present. I don't remember any when I dismantled and rebuilt mine. 

Checked the exploded view diagram and that doesn't show any either. 

Even in this video there seems to be none (look at around 12:28 onwards). 

Assembly Video

However, I think that the noise in your and my case could simply be from improper gear mesh originating from the cylinder not being fully home. You can notice how the cylinder is driven home. I and you may not have been firm enough during this step. 

 

Martin

I can very certainly say that the sound in that video is exactly what i have on my engine and it comes from the gear area. 

[Andy J]

Manish looked again at the exploded view and you are correct that no washer is present so will remove the item and see what happens.

[Andy J]

Removed the washer and tried the conrod in both possible orientations, but the result is the same with gear meshing sounds over part of the shaft rotation. Obviously something is very critical.

 

Agree it sound very like the video, but my second RCV 58CD does not make this noise so cant believe it is correct for this particular engine.

[Manish Chandrayan]

Andy, agree with that when I first assembled the engine and heard the noise I checked on my 91CD and there was no noise in the new 91 .

After trying various remedies I finally gave up and ran the engine.

No recommending you do that. Rather collectively we can find the reason.    

[Andy J]

Re-watched the 91 assembly video again and did note his rotating cylinder sleeve seems to sit just proud of the cylinder casing. Mine is flush but I do believe the cylinder bearing is correctly seated as the cir-clip fits in the cylinder grove correctly. May be worth first removing the cylinder sleeve and cir-clip and tapping down the bearing again.

[Manish Chandrayan]

Yes I too noticed that. But rather than taking out the cylinder will it not be easier to give a few well considered taps to the cylinder to see if it seats a just a lil bit further and cures the issue? 

[Robert Parker]

Hi Andy,

I have just come across this thread. 

From description on the opening thread you say it sounded like a sewing machine.

Is this sound from cold or after the engine has warmed up.

The reason I ask is I once had an RCV CD58 with the same problem a few years ago. I contacted RCV engines and spoke to someone, sorry I cannot remember his name, but he asked me what the serial number was and I recall it was in the low thousands and he asked what fuel I was using and I replied pro-synth 2000 which is the recommended fuel. He went into a lot of detail but basically with the earlier engine the cylinder liner was moving slightly hence the sewing machine sound. He said it could be repaired or offered me 25% discount on a replacement engine on receipt of my old one, I took up the offer and it has run faultlessly since although hardly used recently.

 

Hope this is of some help

Regards

Robert

[Manish Chandrayan]

Robert, isn't the entire cylinder supposed to move (rotate) ? After all It's an RCV. 

 

[Robert Parker]

Hi Manish,

Yes, the entire cylinder does rotate, but it seems that in the early engines it moved up and down slightly when the engine warmed up as there was some play in the circlip holding the cylinder in place according to the chap at RCV, when this first happened with my engine I shut it down and checked it over as well as a lot of club mates did too and I started it up again and when it got warm the same thing happened again and again. I did not attempt to strip down the engine. Just contacted them for advice.

 

Regards

Robert

[Jon H]

Just for info, the pro synth fuel recommendation comes from the final distributor of RCV and not the original manufacturer themselves. If you do some digging and look up the fuel spec RCV themselves recommended you will find the weston fuel is actually not compliant. 

 

Also, the fuel will make no difference in the case of this mechanical noise which is happening when cold (if i am understanding correctly). It sounds to me as though the gear mesh is too tight. This could be caused by something being bent, or distortion when the crankcase is assembled. 

 

If you can, i would take the crank to a local engineering firm and ask them to clock it between centres to see if its straight. If you are local to me i can do it without any trouble

[Manish Chandrayan]

Thank you Robert, that makes sense. 

With so much head scratching going on, I went and checked my engine that was flown twice after the rebuild. 

 

If you folks remember, I too had that unnerving noise when I rebuilt the engine. Neverthless I test ran the engine. The engine did not display any behavior that could be cause for concern. Once the engine was hot the sound did seem to lessen or go away.

 

I was refurbishing a 27/28 year old Goldberg Cub and the engine seemed a good candidate. 

 

After the weekend when the Cub was flown two tanks, have not been able to fly due to Covid lockdown. Do not remember checking for that sound after flying. Guess the engine was fine and I may have forgotten about the should issue altogether. 

 

Today while rearranging some stuff took out the Cub with the RCV and gave it some flips and some slow turns. Miraculously that grating sound is gone. Just not there. 

[Andy J]

Jon are you near MK43 (Bedfordshire) as could well take you up on the offer.

 

From my phone call to Weston last week they did ask if I had an early engine as apparently no circlip was fitted below the cylinder bearing which did allow the rotating piston to move and hence the issue I suspect you had Robert. My engine does have a circlip.

 

So after several re-assemblies of the engine (now without a piston fitted) I went from crunching gears over the full 360 deg rotation of the prop to just a few degrees of every second rotation of the prop.  Given the prop has to turn 720 deg to rotate the cylinder 360 deg I can only assume there is an issue with the cylinder gear rather than the shaft gear. If it was a bent shaft then I would have thought the problem would be seen every rotation of the prop rather than every second

[Jon H]

Hemel Hempstead so not a million miles away. 

 

cant fault your logic on the gear diagnosis. IF it was the shaft i would also expect it to be every revolution. It still could be bent, but something else is likely at play as well

[Manish Chandrayan]

Andy

Just a thought. How particular are you while setting the timing? Are you using any tool etc to ensure equal opening of the ports?

Could it be that the gear mesh does not exactly match due to us being particular with the port opening? Try doing that once just with the eye and see if the mesh improves. I the 91 CD assembly too the guy does it just with the eye/feel

Edited May 17, 2021 by Manish Chandrayan

[Andy J]

The issue is nothing to do with the engine timing Manish as currently I don't have the piston or conrod fitted and I can still hear gear meshing.

 

Given the problem possibly lies with distortion of the case will re-lap the top and bottom engine castings across my 400/1000 diamond sharpening tool which I know to be level. 

 

Up to now have set the engine timing by eye given little adjustment can be made other than +/- one rotation of the cylinder gear.

Edited May 17, 2021 by Andy Joyce

[Jon H]

Assuming its all straight it sounds like its time for some shims to get that mesh perfect. Given the tiny amounts we are probably talking about a thin strip of kitchen foil will probably do the job...assuming we can work out where to put it ?

[Andy J]

After lapping the upper casting surface that interfaces with the lower case the gear meshing is now worse .

 

Tried standing off the lower case by using some off-cuts of litho plate and whilst this did improve things the noise is still present every second rotation of the prop.

 

Suspect the cylinder gear is sitting too close to the drive pinion. Wondering therefore if I could lower the rotating cylinder further into the cylinder by taking off 1/1000 or so on its shoulder that interfaces with the cylinder head bearing.

Edited May 17, 2021 by Andy Joyce

[Jon H]

Are you able to hold the bearings in the crankcase with some small clamps and then rotate it with the bottom half of the case removed? you might be able to see what is going on a little better. 

 

I would also suggest you clean the gears with meths or something to get all the oil off, and then use either engineers blue or a dry erase marker on all the teeth. Put the thing back together, turn it over and look at the wear marks to see what is what. 

[J D 8]

How about getting some engineers blue to try and work out where the unwanted contact is taking place?

It could be that a few gear teeth are just a bit tall and contacting the base of the pinion gear.

[Andy J]

Well after cleaning up the base of the rotating cylinder that interfaces with the cylinder bearing applied heat to the engine casing and cylinder bearing. then drove in the rotating cylinder in the normal manner using a soft headed mallet.  Engine roughly timed by inspection on the exhaust port and the lower casing applied.

 

Thinking I would immediately get the noise back but to my surprise there was none!  Applied all 6 bolts to an appropriate torque. Still no noise but on turning the prop backwards there was a slight noise but not significant.

 

Heated the engine up using my hot air gun and still no noise so back in the model it goes for another test run.