Rod side clearance

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
cgarb
Guru
Guru
Posts: 2006
Joined: Wed Jul 09, 2014 11:50 am
Location: Maryland

Rod side clearance

Post by cgarb »

Building my 421 shortblock, got everything mocked up to grind clearance on the rods for the cam lobes and I checked my rod side clearance and it is at .026" on the two journals that I checked. Does this seem excessive? I assume there is nothing that can be done about it short of buying another crank or different rods.
cjperformance
Guru
Guru
Posts: 3661
Joined: Tue Aug 19, 2008 7:20 am
Location: South Australia

Re: Rod side clearance

Post by cjperformance »

cgarb wrote: Sun Apr 22, 2018 8:08 pm Building my 421 shortblock, got everything mocked up to grind clearance on the rods for the cam lobes and I checked my rod side clearance and it is at .026" on the two journals that I checked. Does this seem excessive? I assume there is nothing that can be done about it short of buying another crank or different rods.
thats .026" divided over 3 points of clearance, about .008" and a bit per clearance point you have no problems. This is oil exit area for the big end bearings, there needs to be enough area to allow enough flow.
Craig.
swampbuggy
Guru
Guru
Posts: 1575
Joined: Mon Apr 04, 2011 8:54 pm
Location: central Florida

Re: Rod side clearance

Post by swampbuggy »

Cgarb, that sounds about correct to me . Mark H.
cgarb
Guru
Guru
Posts: 2006
Joined: Wed Jul 09, 2014 11:50 am
Location: Maryland

Re: Rod side clearance

Post by cgarb »

I found a spec online somewhere for factory type SBC specs and it was .010-.020" my .026" was out of that spec so I was just asking to be sure I wouldn't have any issues with that. Taking my time, checking all my clearance's so I can hopefully have an issue free racing season...well late start to a racing season...lol.
swampbuggy
Guru
Guru
Posts: 1575
Joined: Mon Apr 04, 2011 8:54 pm
Location: central Florida

Re: Rod side clearance

Post by swampbuggy »

Have you ever heard the saying---a little loose, nobody knows. Too tight, everybody knows (when she self destructs) ? David Reher of Reher Morrison Racing engines stated, my feelings on engine clearances in pretty simple i would much rather it be a little loose than on them tight side. Mark H. :wink:
cgarb
Guru
Guru
Posts: 2006
Joined: Wed Jul 09, 2014 11:50 am
Location: Maryland

Re: Rod side clearance

Post by cgarb »

Yes, I have heard that before...I'm a machinist by trade and a bit OCD when building engines. I can't help it... Thanks for the advice. Do you think I could make a .008" thick shim to put between the rods?....just kidding.
cjperformance
Guru
Guru
Posts: 3661
Joined: Tue Aug 19, 2008 7:20 am
Location: South Australia

Re: Rod side clearance

Post by cjperformance »

cgarb wrote: Mon Apr 23, 2018 11:08 am Yes, I have heard that before...I'm a machinist by trade and a bit OCD when building engines. I can't help it... Thanks for the advice. Do you think I could make a .008" thick shim to put between the rods?....just kidding.
Just knurl the sides of the rods :lol:
Craig.
bentvalves
Expert
Expert
Posts: 537
Joined: Mon Dec 12, 2016 3:37 pm
Location:

Re: Rod side clearance

Post by bentvalves »

this topic was just beat to death. Posted the 8th of April 2018.

viewtopic.php?f=1&t=52902
cgarb
Guru
Guru
Posts: 2006
Joined: Wed Jul 09, 2014 11:50 am
Location: Maryland

Re: Rod side clearance

Post by cgarb »

I remember that thread and the issues about excessive oiling...that's not my issue here. I was just concerned about the mechanical ability of excessive clearance keeping the rods 90 deg to the crankshaft. My pistons are not guided at the top so I was worried about one of my rods deciding to take a stage right outside the block. That seems to be not an issue with the general consensus so I'm going to continue on with the build.
Walter R. Malik
Guru
Guru
Posts: 6353
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: Rod side clearance

Post by Walter R. Malik »

cgarb wrote: Sun Apr 22, 2018 8:08 pm Building my 421 shortblock, got everything mocked up to grind clearance on the rods for the cam lobes and I checked my rod side clearance and it is at .026" on the two journals that I checked. Does this seem excessive? I assume there is nothing that can be done about it short of buying another crank or different rods.
The old rule of thumb for connecting rod side clearance is 4 times the bearing clearance, minimum

I don't think you will see any issue.
http://www.rmcompetition.com
Specialty engine building at its finest.
Post Reply