Connecting rod weighing

Tech questions that don't fit above forums

Moderator: Team

Post Reply
belgiquebasterd
Member
Member
Posts: 89
Joined: Thu Sep 15, 2011 4:53 pm

Connecting rod weighing

Post by belgiquebasterd » Sat Oct 15, 2011 4:45 pm

Made my own jig to weigh little and big ends seperately using info I found in other threads on this site as a lead, problem is I can't get consistent repeat readings, the weight differs +/- 2gr.

Picture of the jig, made the chains about 3 foot long to prevent binding issues (same as the example I found in another thread here)

Image

Used an old bearing to hold the big end, is a little bit smaller than the big end diameter as you can see

Image

Used an old lifter body for the small end, there is a bit of play but not much as you can see in the picture

Image

No matter how hard I try I can't get good readings, it's driving me crazy, what am I doing wrong?

Thanks, Christof.

Nick Campagna
Pro
Pro
Posts: 474
Joined: Wed Mar 05, 2008 6:36 pm

Re: Connecting rod weighing

Post by Nick Campagna » Sat Oct 15, 2011 5:58 pm

Off hand, I would say stick-slip on the bearings. Use a knife edge to hold the conrod at each end and lose the bearing and pin arrangement. IMHO.
Is the defect in what I see, or what I'm seeing with ?

donc
Guru
Guru
Posts: 1188
Joined: Sat Dec 04, 2010 9:10 am

Re: Connecting rod weighing

Post by donc » Sun Oct 16, 2011 10:07 am

Nick Campagna wrote:Off hand, I would say stick-slip on the bearings. Use a knife edge to hold the conrod at each end and lose the bearing and pin arrangement. IMHO.
x2Try to keep ctr. of rod bore centered on pin, Id shorten the chain, keep the rod as straight as you can, make sure nothing like compressor or other machine is not vibrating bench,also make sure theres no magnatism in parts that will make it hang up. You can check scale with clean dollar or whatever currency each bill should 1 gram. and no a 10 dollar bill doesnt way 10 grams LOL.

governor
Expert
Expert
Posts: 615
Joined: Sat Jan 17, 2009 2:12 pm
Location: Michigan

Re: Connecting rod weighing

Post by governor » Sun Oct 16, 2011 6:52 pm

I built one a few years ago and used roller skate bearings as they were small in dia with very little rolling resistance. I used them on both ends, with the large end having 3 in a row in the big end aligned at the parting line and the other 2 above the rod as a pivot to allow for any mis-alignment.

I would get very repeatable numbers, using my old beam paint scale.

Gov
a passion for racing

belgiquebasterd
Member
Member
Posts: 89
Joined: Thu Sep 15, 2011 4:53 pm

Re: Connecting rod weighing

Post by belgiquebasterd » Mon Oct 17, 2011 4:42 pm

Victory, well kind off :-), ended up using router bit bearings to hold the rod on and can now get readings wich only vary max 0.3gr. Is this acceptable, what is the usual tolerance used when balancing rods, or do they have to be spot on?

Image

Router bit bearings are just a touch bigger than the bolts, you can barely see them.

Image

Thanks for the help!

donc
Guru
Guru
Posts: 1188
Joined: Sat Dec 04, 2010 9:10 am

Re: Connecting rod weighing

Post by donc » Tue Oct 18, 2011 1:56 pm

Very nice, good job.

Post Reply