074 bent rod
 

[:@] I need to replace the rod in my 074 and was looking for any tips or hints that yall might have. What happen?? well I wanted to fly more than the battery on my glow plug wanted to work and I pushed it too hard. I do have an 061 also I really like these engines and they are my first. Thanks Matt

RE: 074 bent rod
 

Really sorry to hear about your bad luck. I guess it only reaffirms the lesson I learned about small motors a long time ago. Always have a HOT battery and hand start if at all possible.
And your right they are really good motors.
Dennis

RE: 074 bent rod
 

Hey Matt, Dennis is right. I start all my engines by hand. I don't even have an electric starter. At at the initial break in, you can get even the tightest Norvel to fire and run with a smart hand flip at and through the compression stroke. As Dennis stated be sure your bat. will get the glow head very hot(Bright enough that it is uncomfortable to look at). Be carefull with your fuel and priming so you don't hydraulicly lock the motor( personaly I believe this is where 99% of Bent rods on start up occor) and it will start!

Rrragman

RE: 074 bent rod
 

Because the piston is nickle plated, at first blush, it looks like you can't or shouldn't try to replace the rod. However, you can push the pin out without flaking any nickle off. At least I've done it several times on different pistons with no problems.

Drill a hole into a piece of ply larger than the diameter of the pin, say 1/8". Make a punch out of piano wire with a diameter less than the pin diameter. I use old screwdrivers with the tip ground off flush. I have various sizes made up for the purpose.

Align the pin over the hole in the ply and punch it through the piston. It won't punch clean through and slide out because the stake in the piston will hold it so just keep tapping until it clears. When you get a new rod, for what it costs, also get a new pin. Keep track of what side of the piston the pin was driven through. You want to insert the new pin into the same hole that the old one came out of. Tap the new pin in part of the way, just far enough so that you can insert the rod. Then tap it back in all the way. Using the shank end of a drill bit, say 1/4", restake the piston to hold the pin in place. Do this by laying the shank of the bit against the pin hole and roll the piston just slightly forward so that you can tap a new stake onto one side of the hole. Then roll it back a bit to stake the other side of the hole.

You can just tap the pin far enough so that the rod falls out, insert a new rod and tap the pin back in but many times the pin has seen a bit of wear so I refresh this whole area while I'm at it.

RE: 074 bent rod
 

yeah, but they don't sell the rod alone. it is something like 17 bucks for the piston, cylinder and rod assembly.

I use an electric starter ALL THE TIME on my 074. never bent a rod. of course, I don't press too hard. and never put my thumb over intake. my boy bent an 061 rod on a lite machine heli once. flooded it, and continued to choke it. at least he didn't blame his mistake on poor quality:D I applaud you for doing the same!

I'd send you a used engine if I had any spares, but none at this point. you will just have to contact norvel and get the assembly.

RE: 074 bent rod
 

We might be able learn something from full scale engines about starting our 1/2As without bending the internal bits.

If you watch enough World War II aviation footage sooner or latter there will be a sequence showing a ground crew walking the propeller of a radial engine through several cycles. I'm told that turning the engine over by hand, before engaging the starter, cleared oil out of the lower cylinders and limbered everything up before the start. It may have been for other reasons as well.

The simple act of a couple of hand flips before using the electric starter might save a few rods and cranks in our tiny methanol burners.

RE: 074 bent rod
 

All excellent points about proper starting procedures. To expand on both starting and rod failure, see my post called" Beefed up Norvel .074 for diesel operation". I had converted an .074 to diesel and it ran well with excellent throttling. My starting technique was to apply two or three DROPS of prime into the intake. Then, a shot with the starter fires it right off. Never bent a rod doing it this way. The trick is to have the compression and the needle set just right. That done, it takes very little prime to get the engine running.

However, I used an APC 8 X 4 prop at the start and was happy enough with it. Just to experiment, I installed a Cox 8 X 4. The Cox has much more blade area and loads the engine more. With the Cox prop, I bent a rod in the air. Starting was done at idle and no problems were encountered. After acceleration and takeoff, the engine ran fine for a minute or two and then started to sag and misfire. I knew that the compression screw hadn't backed out because there wasn't any!!.

Inspection showed a bent rod. It appears that just that extra bit of load from the Cox prop was too much for the rod.

Pictured is the kind of fix I applied to the stock Norvel mentioned above. What is actually pictured though, is a hybrid with a Cox .09 crank installed into a brass bushed Norvel .074 crankcase. The rod is a bit of overkill but one thing is for sure,,, it'll never bend.

This was done out of concern for breaking a stock crankshaft on massive props. This Norvel hybrid will be dieselized to swing 10 or even maybe 12" props just for the experiment. The idea is for a light engine, chugging away with a scale sized prop, pulling a super light Tiger Moth at scale speeds.

In retrospect, I could have drilled holes in the rod to lighten it without compromisng strength very much and I may do that in the future. However, running as a diesel on big lumber will keep the rpms down along with reciprocating forces.

RE: 074 bent rod
 

Thank you very much for all your help. Matt

RE: 074 bent rod
 

My pleasure Matt, glad to help

Andy

RE: 074 bent rod
 

Did you make that rod or did it come out of the Cox? at any rate someone should show that rod to Norvel, over in the LHS heli forum there are a lot of problems with the rods in the heli version of the Norvel .074...Rog

RE: 074 bent rod
 

Rog,

Yes, I've had some feedback from the heli guys. The rod was custom made. It's similar to the one I made for my stock engine which has been flown extensively. I've been winter flying the past week on diesel and have had a bit more problem with starting as you might expect in the cold weather. Still, the rod is holding up just great. It's really a bit of overkill but it was easier just to make a rod out of flat stock than to try and turn out a "dogbone" rod on the lathe. The next one will have lightening holes to make it lighter.

RE: 074 bent rod
 

Hi Andy,

Do you have the hole center distance for the .074 rod ?

Aaron

RE: 074 bent rod
 

Captain/Aaron,

Didn't actually measure it. I straightened the old rod best I could, then I cyano'd it down to my strip of aluminum and used the existing holes as a guide to drill the new holes. Then I simply dressed the aluminum and removed all material that didn't look like a rod. The material I used was from an old, spring aluminum landing gear. It's quite hard and stiff,, seemed ideal and it IS holding up well so far. Normally when I make a rod, I brass bush both ends while I'm at it. That might not prove necessary with this material. We'll see after a season of flying. Hope so. Small brass bushings CAN be done but are picky and time consuming.

When drilling, don't use the final size drill bit. You're likely to get a hole with too much slop. Drill with a bit just undersize and then final drill with the right bit. This will give you just a tad of clearance that appears to be just right. Your final bit acts more like a reamer. However, depending on the material, sometimes the exact bit leaves a hole that's actually tight on the pin. In this case, that's what happened. I had to take the shank of the bit, and apply a number of cuts with a Dremel wheel to raise very tiny burrs. This was then used to dress the hole to a final perfect, no slop fit. Note that both ends have got two lube holes each.

RE: 074 bent rod
 

Thanks Andy. I think i'm going to try 2024-t3 for the rod, its the set-up in the lathe i'm pounding my brain over ( no mill yet ). Sure would ne nice if i could run off 30-40 at work on the CNC.

Aaron

RE: 074 bent rod
 

Andy Iam having trouble getting a replacement rod. I called Norvel and have left messages but havent had a call back. Do you know of a better way to get parts??

RE: 074 bent rod
 

7075 would be the best alloy to use but 2024 is virtually as strong and shoul do fine -- it's also a little bit easier to machine than 7075 -- but you can't anodize it (not that you were planning to anyway :-)

I use 2024 for a lot of my turning/machining work -- it makes loverly little chips rather than the stringy stuff that 6061 does.

RE: 074 bent rod
 

MADMATT
You might try.
http://www.litemachines.com/
Hope this helps
Joe

RE: 074 bent rod
 

Matt,

Currently, Sig is the distributor for Norvel engines. Justin VanDee is their service man. You might want to give him a try.