connecting rod tolerances

[david cox]

I am trying to determine if the connecting rods on a couple of my OPS 45 engines are still good for another seasons run. While changing bearings on these engines, I made the following measurements:

Engine A: Crank pin OD measures .2350". Bottom ID of rod measures .2370" in the vertical axis, .2365" in the horizontal axis. This rod is 4 years old.

Engine B: Crank pin OD measures .2350". Bottom ID of rod measures .2365" in the vertical axis, .2360" in the horizontal axis. This rod is 2 years old.

Both rods are standard OPS issue, with the (bronze?) bushings. Are these tolerances acceptable?

Thanks in advance,

David Cox

 

[shann harrison]

I'm think the first one replace,The second one is close to being border line.Also check if the oil holes in rod line up with the bushing race cause ops bushings seem to spin a little inside the rod which is a sign to junk them.Plus just by looking at the bottom of the rod if it looks eggshaped to the naked eye junkem.Shann

 

[david cox]

So therefore .002" is too much clearance between the rod and the crank pin? Just wondered what an acceptable clearance might be.

Thanks, David

 

[Brad Christy]

David,

I set all my bushing rods at .0035-.0040" clearance over the crankpin without any problems. At least none that can be linked in any way to crankpin clearance. I've spoken to Rod Geraghty at length about crankpin clearance and came to this conclusion: Until the rod starts hitting the clearance groove in the crankcase, you can't have too much rod clearance. The more clearance you have, the smaller the contact patch, which means less friction. My suggestion to you is this: If you're all that concerned about the bushing being out of round (which is not an issue at all), run a .2375-.2380" reamer through the lower bushing and reinstall the rod. I could easily suggest you buy a new, high-end aftermarket rod for your engine (I'll bet I could make a suggestion as to who you could contact for it, too ), but you'd be wasting your money.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

 

[david cox]

Thanks a lot Brad, I appreciate your help!

-David

 

[J_Moore]

I am trying to determine if the connecting rods on a couple of my OPS 45 engines are still good for another seasons run. While changing bearings on these engines, I made the following measurements:

Engine A: Crank pin OD measures .2350". Bottom ID of rod measures .2370" in the vertical axis, .2365" in the horizontal axis. This rod is 4 years old.

Engine B: Crank pin OD measures .2350". Bottom ID of rod measures .2365" in the vertical axis, .2360" in the horizontal axis. This rod is 2 years old.

Both rods are standard OPS issue, with the (bronze?) bushings. Are these tolerances acceptable?

Thanks in advance,

David Cox

I usually wait till they break and punch a hole in my case just so i know i got the biggest bang for my buck on each rod. I have been doing this for 30+ years and have never had a problem. Hell i found they ran the best when there was a slight crack in the lower end of the rod just to give it that little bit more clearance and man did that thing sing for a 1/4 lap. Its all worth it for me. Another hint is when the motor is sqeeking tight i just runner lean as hell to get that mushroom effect on the rod or as you said( oval shaped) what ever you want to call it that is optimised performance. If i can help at all just give me a call

 

[david cox]

I am trying to determine if the connecting rods on a couple of my OPS 45 engines are still good for another seasons run. While changing bearings on these engines, I made the following measurements:

Engine A: Crank pin OD measures .2350". Bottom ID of rod measures .2370" in the vertical axis, .2365" in the horizontal axis. This rod is 4 years old.

Engine B: Crank pin OD measures .2350". Bottom ID of rod measures .2365" in the vertical axis, .2360" in the horizontal axis. This rod is 2 years old.

Both rods are standard OPS issue, with the (bronze?) bushings. Are these tolerances acceptable?

Thanks in advance,

David Cox

I usually wait till they break and punch a hole in my case just so i know i got the biggest bang for my buck on each rod. I have been doing this for 30+ years and have never had a problem. Hell i found they ran the best when there was a slight crack in the lower end of the rod just to give it that little bit more clearance and man did that thing sing for a 1/4 lap. Its all worth it for me. Another hint is when the motor is sqeeking tight i just runner lean as hell to get that mushroom effect on the rod or as you said( oval shaped) what ever you want to call it that is optimised performance. If i can help at all just give me a call

Hey Jeff thanks a lot for your advice- LOL. I will have to give one of your speed secrets a try as well: This is where you sprinkle a little sand in the carb while the engine is at full throttle on the stand- this creates a lapping compound and gives the perfect piston/sleeve fit that we are all looking for.

-David

 

[Tim Kish]

I know were Jeff learned the sand in the carb speed secret.

He learned this from racing at the old Norwood pond in the early nineties.

You could'nt keep the sand out of your engines if you tried :lol: .

Tim K

 

[J_Moore]

I know were Jeff learned the sand in the carb speed secret.

He learned this from racing at the old Norwood pond in the early nineties.

You could'nt keep the sand out of your engines if you tried :lol: .

Tim K

Yep wasn't sure if i was compressing sand or glow plug elements my piston was so dam pitted

 

[Nigtmare]

I know were Jeff learned the sand in the carb speed secret.

He learned this from racing at the old Norwood pond in the early nineties.

You could'nt keep the sand out of your engines if you tried :lol: .

Tim K

Yep wasn't sure if i was compressing sand or glow plug elements my piston was so dam pitted

Jeff I don't know what you are compressing but what ever it is sure makes you little boat go like H@ll!!! The last time I saw you running I was impressed. :blink: R U coming out to play this year? Nick

 

[Nigtmare]

Hey David!!! Y worry About the rod clearance. Just do what I have told you !!!change the prop move the strut lean the carb and move the pipe All at ones:huh: then watch the boat go!!!! :lol: :lol: Nick

 

[J_Moore]

I know were Jeff learned the sand in the carb speed secret.

He learned this from racing at the old Norwood pond in the early nineties.

You could'nt keep the sand out of your engines if you tried :lol: .

Tim K

Yep wasn't sure if i was compressing sand or glow plug elements my piston was so dam pitted

Jeff I don't know what you are compressing but what ever it is sure makes you little boat go like H@ll!!! The last time I saw you running I was impressed. :blink: R U coming out to play this year? Nick

Hey Nick

I hope to be coming out to a few races anyway. See you there.

Jeff

 

[david cox]

Hi Nick, thanks for the reply. I agree with you that MANY changes should be made at once. If the boat won't work well why not make as many changes as possible, and all at the same time, preferably in the middle of a race: Try new prop, shorten the pipe, lean her in 2 or 3 more turns, go to higher nitro content, colder plug, lower the strut, change the turn fin and go to smaller fuel line......Then watch that baby screaaaam!!!

-David