I have a 3W-100 that may need rod bearings. Are the US distributors (Cactus Aviation or Aircraft International) equipped to split the crank, install new crankpins, con rods and bearings, and press it back together? Or do they just sell you a new crankshaft assembly?

Anyone had this type of work done on their engine? Who did the work and were you satisfied with the job?

Hi Diablo,

Since nobody else posted, I would suggest contacting RCign because he has the equipment to straighten crankshafts. He may have some experience with these split twin cranks.

I have a 3W 50i engine (half of your 100) apart and noticed that even this single cyl. engine has a pressed-together crank that traps the needle bearing. I would have the same problem with my single cyl. if the lower needle bearing went bad.

The 50i lower needle bearing measures 12mm dia. (.472) by 10mm (.394) length. Seems smallish compared with .433 crank pin dia. on a 35 cc OS BGX or .513 dia crank pin on a ST 4500. The latter two engines have bronze bushed rods, tho.

This is starting to sound like the Red Line Oil thread of June 3.

http://www.rcuniverse.com/showthread...806&forumid=37

Brucee

I talked with Gerhard at AI about the engine. Rod bearings are replaced on an exchange basis. They send your crank assembly out for rebuilding and you get one off the shelf for quick turnaround. I pulled the cylinders off myself and found there was nothing wrong with the bearings. The radial play was nil. The pistons were carboned up and the ring on one piston was stuck in the land. I cleaned it all up using Loctite Chisel gasket remover (per Gerhard's advice), put it back together and ran 3 test flights today. The engine is a lot quieter on a cold startup. The compression is better than it was, but still a little soft. The rings probably got distorted when I removed them from the pistons. I have a new set of pistons and rings on the way from AI. I'll put a little more flight time on the motor to try and break-in the old rings before I put the new set in.

I really don't know why the motor was carboned up from about 400 flights with Redline Allsport synthetic at 50:1. One theory I read about on the net was that outboard boat mechanics found that 87 octane gasoline sold over the last few years is unusually prone to carbon build up. They claim this doesn't happen with 89 octane gas or higher. It isn't the octane rating, but the chemical makeup of the gasoline. I've been running the engine exclusively on 87 octane gas. I'll switch to higher octane and see if it makes a difference in the long term.

Hey Diablo.

I can vouch for Gerhard's knowledge of the 3W's. I had a 150 that didn't run right from the git go, but was crashed first flight so just figured it was damaged. Gerhard found manufacturing error, and hense fixed it under warranty, as the crash had no effect on it.

One side of the crankcase was a smidgen thicker than the other creating poor compression on the shorter side!!! He used the good parts and created a very strong engine that I am extremely happy with.

I wouldn't hesitate to send any of my 3W engines to him. He has also been extremely easy to talk to and takes the time to listen and deal with the cause of your call.

Ed

Diablo-
I had the same problem on my 100, I switched to the 3-W oil after I replaced the rings(They were stuck in the grooves), 200 flights since then with no carbon, and I have used "Mid-Grade" 89 octane gas since new. We'll see what the new 200 I bought does.

Bigplaneflyer,

What brand and grade of oil did you use before replacing the rings on your 100?

Thanks,

Bruce

Klotz 80% Synthetic, 20% Castor, the Castor was the culprit. I should have read the label closer!!!!!

I put in the new pistons and rings, the engine runs a little better (100 rpm stronger), however it still clicks....sounds like the valves need adjustment ...q;}

I had the cylinder off again after about 4 gallons of Amoco 93 octane and Redline synthetic--absolutely no deposits. My buddy Terry noticed that the rod has an unusual amount of side play between the crank cheeks (.076") on the right cylinder, didn't check the left cylinder. I've never seen an engine with this much side clearance on the rod. We're wondering if this is part of the design or perhaps the crank pin has slipped out of the cheeks?

Will call Gerhard on Monday to find out what the rod clearance should measure.

The click is from clearance between the rod and crankpin, and/or side play of the rings in the piston grooves....Not to worry..The press fit between the crank and pin is so tight it can't slip...If it was loose enough to slip the crank would twist so bad it wouldn't turn...
Most engine manufacturers are pretty close mouthed about their designs..It's doubtful 3W will release any specs...

Update..I just measured both rods in a new lightweight 150..
The clearance between the side of the rods and the crank cheeks is .110...The rods are narrower than the big end roller bearing cage..The clearance between the bearing cage and the crank is .021..
this particular crank is going back..The taper and threads on the end are ground off center to the bearing diameter, causing a big wobble at the hub..There is no sign of having been crashed..No one is perfect, not even 3W.....

Thanks Ralph, you're information is right on. AI thinks the clicking is just the rings moving freely in the piston lands, and will go away when they get a little carboned up. In the mean time, I'll just follow the advice of the tappet brothers - "just turn up the radio so you don't hear the noise".