Barnboy's 1984 ATC200M Rebuild

[BarnBoy]

Can ATC200 cylinders be bored over 66mm?

Also the screw for the rocker shaft retaining plate is more or less stripped. It's got a flat head screw. Tried carefully heating in case of loctite and still no go. Anyone have success with left-hand drill bits for removing stuck screws? Is it kosher to run old rockers on a new cam??

[ArizonaATC]

Can ATC200 cylinders be bored over 66mm?

Also the screw for the rocker shaft retaining plate is more or less stripped. It's got a flat head screw. Tried carefully heating in case of loctite and still no go. Anyone have success with left-hand drill bits for removing stuck screws? Is it kosher to run old rockers on a new cam??

to 67mm I'm pretty positive.

[BarnBoy]

Ok thanks.

So today I measured the bore....it mics 65.75mm. This doesn't make sense. Its got a piston stamped 50, which I'm positive means 0.50mm oversize. Should the cylinder not measure 65.50mm then?? This same piston that is stamped 50 measures 65.65mm. Can anyone explain how oversize pistons and cylinder work? I am confused.

[Dirtcrasher]

Yes, I have 67mm pistons or 1st gen, it's probably the last bore thou...

[BarnBoy]

How much play is ok in the wrist pin/small rod end? The pin I pulled out of the engine had a fair bit of play, so I tried a spare pin I had that mics like new. It has a very tiny bit of play, but feels pretty tight. Doesn't it need a little play for lubrication? Slides in and out pretty easily. Doesn't appear really egged or anything.

[barnett468]

How much play is ok in the wrist pin/small rod end?

Doesn't it need a little play for lubrication? Slides in and out pretty easily.

Yes it needs a little play for lubrication, however, it doesn't need much play or much oil, because it doesn't rotate much in the rod, but the better the oil, the less potential there will be for it to gall if the clearance is on the tight side etc.

I can't find the clearance tolerance in the manual although it may be there somewhere, and you can't go by the max allowable pin and pin bore wear because that will give you .005" clearance, which is far too much unless you are selling it. In general, for your app, you can safely get away with around .0006" to .0012", although it won't grenade if the clearance is a little more but it might make a little noise.

Pin = .5980 thru .5906

Connecting rod small end = .5909 thru .5930

Page 7-1 & 10-1

http://www.oscarmayer.net/atc/manual...shopmanual.pdf

[BarnBoy]

Yes it needs a little play for lubrication, however, it doesn't need much play or much oil, because it doesn't rotate much in the rod, but the better the oil, the less potential there will be for it to gall if the clearance is on the tight side etc.

I can't find the clearance tolerance in the manual although it may be there somewhere, and you can't go by the max allowable pin and pin bore wear because that will give you .005" clearance, which is far too much unless you are selling it. In general, for your app, you can safely get away with around .0006" to .0012", although it won't grenade if the clearance is a little more but it might make a little noise.

Pin = .5980 thru .5906

Connecting rod small end = .5909 thru .5930

Page 7-1 & 10-1

http://www.oscarmayer.net/atc/manual...shopmanual.pdf

Thanks!! My rod small end id is 0.5914. The spare piston pin I have measures 0.5905. So I have right around 0.0009"-0.001" clearance. The rod end is ever so slightly egged, maybe 0.0003-4" max. I don't think that's anything to really worry about?? There's just barely a tiny bit of noticable play, but it's pretty tight.

If this rod checks out that would be awesome cause I don't really want to spend $200 on a new one if I don't need to. It's got 0.012" side to side clearance, and I can feel absolutely no up/down play.

[barnett468]

I for one would not worry at all about the egg shape and assure you it wont be a problem in your particular app.

[barnett468]

Also, if there is no hole in the top of the rod, you can increase the amount of oil to the pin by drilling a 3/32 hole in the top then radiusing the entrance a little with a bigger drill or dremel etc then be sure to sand the inside of the rod slightly where the hole is with around 800 grit paper to remove metal from around the edge of the hoke that might be protruding slightly into the pin hole.

[barnett468]

Also, if there is no hole in the top of the rod, you can increase the amount of oil to the pin by drilling a 3/32 hole in the top then radiusing the entrance a little with a bigger drill or dremel etc then be sure to sand the inside of the rod slightly where the hole is with around 800 grit paper to remove metal from around the edge of the hoke that might be protruding slightly into the pin hole.

[BarnBoy]

I for one would not worry at all about the egg shape and assure you it wont be a problem in your particular app.

Thats what I wanted to hear Once you start getting into 10 thousandths thats getting pretty small!

I'll have to check if its got a hole. I'm not real keen on drilling my good rod tbh. Will it make that much of a difference? Its got 2 good sized holes on the top sides already.

[barnett468]

Thats what I wanted to hear Once you start getting into 10 thousandths thats getting pretty small!

I'll have to check if its got a hole. I'm not real keen on drilling my good rod tbh. Will it make that much of a difference? Its got 2 good sized holes on the top sides already.

It won't hurt a thing to add a hole to it, and yes, it will increase oil flow to it. Is it overkill....well, that depends on how you look at it, but the undeniable fact is that the hole in the rod is egg shaped a little and the pin is worn, and more oil and/or better oil, and/or more frequent oil changes etc would have reduced the wear, and that is a guarantee. If it already has holes in the top like the one I mentioned, you don't need another one, but it might benefit from them being slightly larger and radiused if they currently are not.

Can you post a photo of the holes you are referring to?

[BarnBoy]

Yeah, here's a pic. They aren't directly on the top, but on the top half.

[barnett468]

Yeah, here's a pic. They aren't directly on the top, but on the top half.

xln't, you don't need another hole.

.

[BarnBoy]

xln't, you don't need another hole.

.

Awesome! I was looking at it like....man if it don't get enough oil through those 2 holes something's wrong.

Hoping to get the bottom end tore apart as soon as time allows. Finally got the printer fixed and shop manual printed out. I like to have it right there and go step by step, especially since this is my first bottom end.