[bluegoat65]

My next build I m going to use aluminum rods with custom length, piston pin and crank pin diameters. I would like to go with an 2.00 inch crank pin diameter. I ve heard of guys doing this. In researching this no one seems to make an custom rod bearing in this diameter with even an Big Block Chevy width. Is this something that has to go to the extreme of welding the crank journal and reginding to small block chevy width? My reasoning for the 2.00 pin is that I want to offset stroke the crank abit (without welding) and thought I would take advantage of the friction reduction that I could also get out of it. Anyone with an opinion?

[Half-Inch Stud]

2.2" bearings with pin hole are easy to get.

Seemed tough for me to get 2.2 rod bearing +060 (is that 2.140"?) with pin hole.

Probably reasearch non-V8 rod bearings for 2.0" huh.

[steve25]

Stroke adds far more fiction then bearing diameter does. Myself I do not think that going thru the gyrations to get a smaller bearing is worth it unless the motor will spend alot of run time ( like getting to 6800 and never dropping lower) above 7k rpm.
It sounds like you will have a nice light weight rotating assy and thats what time and effort should focus on.
With the direction it sounds like your heading you should be using pistons with compression rings of less than 1/16".

[bluegoat65]

Well to get more specific, the goal is an 3.800 stroke with 7 inch rod and an 4.210 bore. If the cylinders sonic out with enough on the thrust side of the bore for an 4.250 bore I m going to go with that. Mind you I plan to full fill the block solid and plug the deck. Just going to cool the heads. This will be an drag only motor. And yes the plan is to go with .043 top and second rings with an 3.0 mm oil control. Napier style for the 2nd ring to help handle the oil the low tension 3rd ring will be giving up. Going to 4 bolt the center mains. Longevity is what I m after. So figured ridged light weight parts and dampening is the key. I only want to tear down for freshening. Rather be racing then dealing with broken parts.

[BruceWilkie]

I think you can get 3.8 stroke with BBC rod end... your movin the pin center .025". Probably take an 10 under bbc bearing to clean up. SBC 2.1" or 2" bearing is ok... the rod can be wider than the bearing. Not so sure I'd go all the way to 7" rod length... IMO get best ring pack and placement then find your pin height from there... Then determine rod length... Get your rods/pins from BME... and dont hesitate to talk with them.

[john marcella]

Originally Posted by bluegoat65

My next build I m going to use aluminum rods with custom length, piston pin and crank pin diameters. I would like to go with an 2.00 inch crank pin diameter. I ve heard of guys doing this. In researching this no one seems to make an custom rod bearing in this diameter with even an Big Block Chevy width. Is this something that has to go to the extreme of welding the crank journal and reginding to small block chevy width? My reasoning for the 2.00 pin is that I want to offset stroke the crank abit (without welding) and thought I would take advantage of the friction reduction that I could also get out of it. Anyone with an opinion?

The width of the rod sets the rod end play, the bearing can be real narrow as long as the oil hole in the crank is not exposed.

[bluegoat65]

Well that was simple. Just use the standard small block Chevy bearing. First thing that came to mind when I saw the responses was with an narrow rod bearing would there be any tendency for the rod to rock and stress the pin end? The piston arrangement I plan to use is the same as the 4.25 stroke with 6.800 rod setup that seems to be the popular setup out there with the bigger cube guys. A little decking to square things up should bring the quench in. Butlers have an nice Ross short pin style they just put out there, but still uses the heavy ring pack. I personally like the CP brand. I have to say, the 7 inch rod makes for an awesome rod stroke ratio on paper and the trade off in weight with extra rod length versus piston weight with the higher pin location may equal out versus shorter rod and heavier piston due to lower pin height.

[john marcella]

Originally Posted by bluegoat65

Well that was simple. Just use the standard small block Chevy bearing. First thing that came to mind when I saw the responses was with an narrow rod bearing would there be any tendency for the rod to rock and stress the pin end? The piston arrangement I plan to use is the same as the 4.25 stroke with 6.800 rod setup that seems to be the popular setup out there with the bigger cube guys. A little decking to square things up should bring the quench in. Butlers have an nice Ross short pin style they just put out there, but still uses the heavy ring pack. I personally like the CP brand. I have to say, the 7 inch rod makes for an awesome rod stroke ratio on paper and the trade off in weight with extra rod length versus piston weight with the higher pin location may equal out versus shorter rod and heavier piston due to lower pin height.

Why do you want a 7 inch rod?

[cgeise]

will the 1.88 bearing work for your application ?

[bluegoat65]

Piston dwell, to Johns question.

[bluegoat65]

I like your thinking...cgeise, I know Rousch/Yates carries somthin there for the smallblocks in an 1.88..I ll have to do some research on that. Thanks.

[john marcella]

Originally Posted by bluegoat65

Piston dwell, to Johns question.

What about were peek piston speed occurs now vs the crank angle you make the most cyl pressure? What about the effects it has on the exhaust valve timing because you now have just LOST TIME from the most efficient piston position to BBC.

Remember the most cyl pressure is made shortly after TDC. The most efficient piston position is when the crank throw and connecting rod are 90* to one another. ( The crank gets the most rotation vs piston movement)
The shorter the rod the sooner this occurs.

[cgeise]

Originally Posted by bluegoat65

I like your thinking...cgeise, I know Rousch/Yates carries somthin there for the smallblocks in an 1.88..I ll have to do some research on that. Thanks.

Its my undersdtanding the 2.00 rod has been done in the BBC for quite a while and the 1.88 in BBC and sbc also --

[BruceWilkie]

Personally I'd run a BME rod at stock rod length maybe shorter... unless you go too small a crankpin, a bit heavier piston than you are thinking of isnt going to hurt the rod none. The aluminum rod is a shock absorber and I wouldnt sacrifice too much rod journal off a cast crank...keep it strong.

[bluegoat65]

John, doesn t your short rod require a much better flowing head than an long rod motor due to its lack of dwell time and a long rod actually makes better running compression than a short rod. To get the same running compression would require an short rod to have to increase its static compression to have equal output. Plus I don t need as high of an efficient intake port as a short rod motor would need. Exhaust side, well I think cam timing may help me there.

[cfmcnc]

Got something going together with a 1.850 rod pin dia .Clevite 1798H bearing.Bill C.

[john marcella]

Originally Posted by bluegoat65

John, doesn t your short rod require a much better flowing head than an long rod motor due to its lack of dwell time and a long rod actually makes better running compression than a short rod. To get the same running compression would require an short rod to have to increase its static compression to have equal output. Plus I don t need as high of an efficient intake port as a short rod motor would need. Exhaust side, well I think cam timing may help me there.

Cam timing can help you on the intake side not the exhaust side . That's the point you lose valuable time on the ex side with the longer rod. Only remedy is big ex CS.

[J.C.you]

there is a nice piece 3.75 billet with a 2" pin in the for sale section.