Can an engine with a bad bearing still run perfectly?
 

One of my GRP .21's is making a weird almost rattling sound right after you rev it and also right before it dies from loading up at idle. The engine is running perfect and I don't see any fuel around the front of the case to indicate the bearing leaking. It is running excellent except for this noise I can't figure out.

Could it be a clutch spring or clutch noise?

Could be a clutch bearing or the rod starting to loosen up. If the tires arnt trying to spin at idle its not a clutch spring. If the bearings inside the motor are starting to go bad it will get very loud and you will have alot of idle problems.

They weren't trying to spin.

I have Zero idle problems. I bought this used with supposedly only a couple gallons at most on it so I doubt it could be the rod. Maybe I will get lucky and it's just a clutch bearing. I'm fixing to pull the engine out now and see if I can find anything.

Over-rev any engine (new or used) and it takes a major toll on the engine, rod, bearings, piston, etc.

Friend of mine, had a runaway (long story), the car ended up on it's lid, revving at full throttle until it burned up the fuel in the line. Didn't know it caused any terminal damage, until it was fired up for the next run, when the rod let go, taking out the cylinder in the process.

I know I haven't over revved it at all. But I don't know about the previous owner. I might tear it all the way down and take a look at the rod and both bearings.

I'm curious about this as well. I have an engine with about 3 gallons on, but I didn't but the first 2 on it. Ran great for the first half gallon I had it, and still runs good. However, now if you listen close you can hear what almost sounds like steam in the engine, or a low hum that isnt normal. think/assume it is the main engine bearing going. I'm going to try to replace it with a cheap tko.

I just tore it down. The piston and crank look great along with the rod. But the rod has a tick too much play on the crank pin I think.

If I put the piston at tdc and rock the crank back and forth you can hear a distinct tick from the slack in the rod.

Both bearings look and feel great. Ya'll think it's the rod?
And if so is there anywhere I can get a rod that fits this GRP?

Simple check on the rear bearing if you can hear a abnormal sound when the engine are running: At idle hold your hand on the head - don't burn yourself! If the abnormal sound disappears the rear bearing are defective. Change the front bearing at the same time.

It makes the noise at low rpms only from what I can tell. You can really hear it well when the engine chokes out at idle if I let it load up.

And it won't do it constantly. It's when ever it wants to unfortunately. The sound will not stay constant. Might go 5-6 seconds in between noises sometimes a little longer.

Check if your crank pin is out of round with some calipers. If its not then pick up a rod from a tecnopower engine they are compatible with the ole GRP engines I belive. However check for corrosion or looseness of the rear bearing, I have had one that felt good but the car ran like crap till I changed it. However what your symptoms are sounds to be the rod. Previous owner may have had a run-away, or simply lied about engine age.

I don't even know if I can find a techno rod since they are closing down. I will try amain first. Any other places have techno parts?

EDIT: Just tried Amain with no luck. They have everything except for rods.

i had a nova plus 4 that did this, i found out the pinch was tight and the knocking noise i heard was the pistion hitting pinch really hard. sounded like a rod knock in a 1:1 car. after engine was broken in after to tight of a pinch it no longer made the noise

ascendancy g5 rod will fit the grp

If its engine noise. Its could be that your conrod bushing or the crank pin are worn. Check also the main bearing for play. These conditions will make the conrod hit wall of the crankcase resulting a loud noise and tuning issues. This happened to my picco(bearing) and grp(conrod).

TQ speed lab rods will fit as well. Don't know if they are still available.