Topic: Cobra motor disassembly and rebuild

[Bill/BentON Racing]

With ring package, 220 grams, pin 39 grams.

[dragracer]

Dude, you're finally making me happy. Should have pulled the whole damn thing apart to begin with. Remember, when you buy a used engine, you go into the purchase knowing its just a parts motor. I don't care what the previous owner tells you about its condition. I'm speaking from experience here. And know you've gone through this at least two times already - got it now??

[gschuld]

With ring package, 220 grams, pin 39 grams.

Good deal.

Were the pins held in position with Teflon buttons?

George

[dragracer]

So what size bore???

[gschuld]

They are RC Arias 73s Frankie.  Stamped:

 RC ENG
   73H

under the crown.

George

[dragracer]

Those Arias 73mm pistons I have are 190grams. Didn't weigh the rings or pins. In fact the 72mm KZ pistons I have are only 208grams with the rings, pin was 18 grams. Wisecos. What a difference the years make in piston design and material weight.

[gschuld]

Pin was 18 grams?  Misprint I hope... 

FWIW, the old ring packs for the RC and MTC pistons average 23 grams per piston.

George

[Bill/BentON Racing]

Stocker around 40 something . Lightweight ones usally about 10 grams less.

[dragracer]

Pin was 18 grams?  Misprint I hope... 

FWIW, the old ring packs for the RC and MTC pistons average 23 grams per piston.

George

I'll weigh it again tomorrow but I'm pretty sure that's what it weighed.

[NickO]

Some epoxy filler from the inlet port broke loose and jammed in the chamber?

[Bill/BentON Racing]

Close. It's a piece of foreign material. We use them all the time......Let's see engine out,been in engine room for a couple months , plugs out....hmmmmm checked with boroscope and blew air in plug hole... should have opened a valve and blew through there. The air moved it that you could see. So what is it? Pic later, Bill

[MRieck]

I never liked that. Going to replace em with better ones, better head nuts also and cylinder stud kit. New cam chain and primary's etc, new mains also. This 1/2 ready for a bath. I cleaned my lens. BF chew toy closest so far!! Closest guess wins a John Stein Drag Racing book!

I have to say the big ends of #2 & #3 rods weigh a noticeable amount less after grinding those steel rod bolts down. Whoever built it should have cut all the bolts to the same size. Why bother balancing the crank?
 This is the kind of stuff I have noticed when disassembling old performance motors.....a lot of sloppy, get it done attitude work.
  Maybe it is ticky tack but it bugs the crap out of me and, as Frank said, demands the complete disassembly of any of these things. 

[bear]

I have to say the big ends of #2 & #3 rods weigh a noticeable amount less after grinding those steel rod bolts down. Whoever built it should have cut all the bolts to the same size. Why bother balancing the crank?
 This is the kind of stuff I have noticed when disassembling old performance motors.....a lot of sloppy, get it done attitude work.
  Maybe it is ticky tack but it bugs the crap out of me and, as Frank said, demands the complete disassembly of any of these things. 

Yep gotta agree. You might be able to bolt on HP, but you can't bolt on reliability.
That comes from doing the little things right.

[MRieck]

Pin was 18 grams?  Misprint I hope... 

FWIW, the old ring packs for the RC and MTC pistons average 23 grams per piston.

George

I'll weigh it again tomorrow but I'm pretty sure that's what it weighed.

2 teflon buttons weigh 10 grams Frank.

[gschuld]

You might be able to bolt on HP, but you can't bolt on reliability.

That's a good one

George

[dragracer]

Pin was 18 grams?  Misprint I hope... 

FWIW, the old ring packs for the RC and MTC pistons average 23 grams per piston.

George

I'll weigh it again tomorrow but I'm pretty sure that's what it weighed.

2 teflon buttons weigh 10 grams Frank.

I'm probably way off the mark on my pin weight then. Lol. A mind is a terrible thing to waste. Blame it on old age.

[NickO]

I never liked that. Going to replace em with better ones, better head nuts also and cylinder stud kit. New cam chain and primary's etc, new mains also. This 1/2 ready for a bath. I cleaned my lens. BF chew toy closest so far!! Closest guess wins a John Stein Drag Racing book!

I have to say the big ends of #2 & #3 rods weigh a noticeable amount less after grinding those steel rod bolts down. Whoever built it should have cut all the bolts to the same size. Why bother balancing the crank?
 This is the kind of stuff I have noticed when disassembling old performance motors.....a lot of sloppy, get it done attitude work.
  Maybe it is ticky tack but it bugs the crap out of me and, as Frank said, demands the complete disassembly of any of these things. 

You and I sound like we could put the world to rights Mike, the older I get the more pedantic I become? I look forward to sharing a beer sometime maybe....who knows?

Happy Christmas BTW.

[NickO]

Close. It's a piece of foreign material. We use them all the time......Let's see engine out,been in engine room for a couple months , plugs out....hmmmmm checked with boroscope and blew air in plug hole... should have opened a valve and blew through there. The air moved it that you could see. So what is it? Pic later, Bill

Discarded ear-plug maybe (or a Leprechaun)?

[madmtnmotors]

Almost looks like one of the valve keeper wedges? Dropped down the spark plug hole during assembly?

[754]

Looked a bit like a dowel to me , maybe like the camholder size...

[Jerry Rxman Griffin aka MuthaF'er]

Close. It's a piece of foreign material. We use them all the time......Let's see engine out,been in engine room for a couple months , plugs out....hmmmmm checked with boroscope and blew air in plug hole... should have opened a valve and blew through there. The air moved it that you could see. So what is it? Pic later, Bill

Roach clip?? 

[Medyo Bastos]

[/quote]

Roach clip??
[/quote]

maybe if he was in denver


...Save a tree, eat a beaver...

[gschuld]

Close. It's a piece of foreign material.  We use them all the time......, Bill

Roach clip??

LOL.  Damn that was funny...

George

[MRieck]

I never liked that. Going to replace em with better ones, better head nuts also and cylinder stud kit. New cam chain and primary's etc, new mains also. This 1/2 ready for a bath. I cleaned my lens. BF chew toy closest so far!! Closest guess wins a John Stein Drag Racing book!

I have to say the big ends of #2 & #3 rods weigh a noticeable amount less after grinding those steel rod bolts down. Whoever built it should have cut all the bolts to the same size. Why bother balancing the crank?
 This is the kind of stuff I have noticed when disassembling old performance motors.....a lot of sloppy, get it done attitude work.
  Maybe it is ticky tack but it bugs the crap out of me and, as Frank said, demands the complete disassembly of any of these things. 

You and I sound like we could put the world to rights Mike, the older I get the more pedantic I become? I look forward to sharing a beer sometime maybe....who knows?

Happy Christmas BTW.

Thanks Nick and the same to you. I don't think I'm up to the job of putting the world to rights but a motorcycle engine is a task I can handle.
 And I shouldn't just say "older" performance engines.....I have seen some real bonehead stuff in modern engines too

[dragracer]

Come on Bill, go ahead and let us in on the truth. I know you were waiting for someone to beg you. Lol