Connecting Rod Clearances

jrstock · 06-18-2017, 07:45 PM

Looking for thoughts on how to fix a recent problem. I have dial bore gaged and verified with plastigage that I am seeing .001 clearance on connecting rod journals.

I have looked to find a .001X oversize bearing to increase the clearance. However the connecting rod journals are ground .030 and manufacturers do not make an oversize bearing at this size.

Any ideas on how to open the connecting rod clearance up to .0015-.0020?

Can the crank be ground down by .0005 to open the clearance?

If so any recommendations on who can do so?

Thank you in advance!

richie 2 · 06-18-2017, 08:55 PM

the rod housing bore could be on the small side of that tolerance...

Larry Hill · 06-19-2017, 07:08 AM

Try a different brand of bearings. I think it's best to size the rod, instal bearings, subtract clearance, then resize crank. Also look at the backside of bearing for for bruses in the metal, trash inbeded on the back side, or flash from a plating. Almost forgot, check the tang fit.

Dwight Southerland · 06-19-2017, 08:17 AM

Use micrometers - inside and outside. Plastigage will not give you accurate measurements. Waste of time and effort.

Todd Gross · 06-19-2017, 02:48 PM

Yes to all of the above.
Don't use plastigage.
The connecting Rod Bores can be resized to the high side of tolerance. They at least need to be clean ,straight and round.
Different Bearing manufacturers do vary in size as Mr. Hill stated. In my findings Clevite 77 are the tightest fit, Speed Pro / Federal Mogul tends to be about .0001 to .00015" bigger and recently I have been seeing King XP bearings closer to .0002" or more than a Clevite.

Larry Hill · 06-25-2017, 09:25 AM

So what did you do?

carl hinkson · 06-25-2017, 10:50 AM

Quote:

Originally Posted by Dwight Southerland

Use micrometers - inside and outside. Plastigage will not give you accurate measurements. Waste of time and effort.

Believe me compared to some of the cheap bore gauges out there. NEW Plastigage its not that bad is pretty simple how a piece of waxed string works.

I have guys check my clearances with it seem to right in line with what I set them at with my Sunnen Bore gauge.

Here is are some good threads on checking bearing clearances.

http://www.performanceboats.com/gn7-...learances.html

http://www.speedtalk.com/forum/viewt...a58c2&start=15

jrstock · 06-26-2017, 09:21 PM

Follow Up

I found on a past classracer post that is very difficult to take a few tenths off a connecting rod journal.
http://www.classracer.com/classforum...ad.php?t=53273

These were the other options I looked at:

1) Polish connecting rod journal

2) Hone Rod Big End

3) Grind Crank to .040 Under

In the end swapped to another crank rather than risking any of the above options.

Thanks for the advice!

06-18-2017, 07:45 PM	#1
jrstock Junior Member Join Date: Feb 2015 Posts: 16 Likes: 0 Liked 0 Times in 0 Posts	Connecting Rod Clearances Looking for thoughts on how to fix a recent problem. I have dial bore gaged and verified with plastigage that I am seeing .001 clearance on connecting rod journals. I have looked to find a .001X oversize bearing to increase the clearance. However the connecting rod journals are ground .030 and manufacturers do not make an oversize bearing at this size. Any ideas on how to open the connecting rod clearance up to .0015-.0020? Can the crank be ground down by .0005 to open the clearance? If so any recommendations on who can do so? Thank you in advance!

06-18-2017, 08:55 PM	#2
richie 2 Senior Member Join Date: Feb 2009 Posts: 971 Likes: 425 Liked 205 Times in 93 Posts	Re: Connecting Rod Clearances the rod housing bore could be on the small side of that tolerance...

06-19-2017, 07:08 AM	#3
Larry Hill Live Reporter Join Date: Oct 2004 Location: Hickory, Ky Posts: 10,633 Likes: 1,927 Liked 10,687 Times in 2,225 Posts	Re: Connecting Rod Clearances Try a different brand of bearings. I think it's best to size the rod, instal bearings, subtract clearance, then resize crank. Also look at the backside of bearing for for bruses in the metal, trash inbeded on the back side, or flash from a plating. Almost forgot, check the tang fit. __________________ IHM Used Parts https://ihmusedparts.com 888-821-1817

06-19-2017, 08:17 AM	#4
Dwight Southerland VIP Member Join Date: Dec 2001 Location: Arkansas - In the middle of everything. Posts: 2,000 Likes: 64 Liked 777 Times in 193 Posts	Re: Connecting Rod Clearances Use micrometers - inside and outside. Plastigage will not give you accurate measurements. Waste of time and effort. __________________

06-19-2017, 02:48 PM	#5
Todd Gross Member Join Date: Mar 2016 Location: Crete, IL Posts: 167 Likes: 260 Liked 54 Times in 24 Posts	Re: Connecting Rod Clearances Yes to all of the above. Don't use plastigage. The connecting Rod Bores can be resized to the high side of tolerance. They at least need to be clean ,straight and round. Different Bearing manufacturers do vary in size as Mr. Hill stated. In my findings Clevite 77 are the tightest fit, Speed Pro / Federal Mogul tends to be about .0001 to .00015" bigger and recently I have been seeing King XP bearings closer to .0002" or more than a Clevite. __________________ Todd Gross 3323 FS/E,F

06-25-2017, 09:25 AM	#6
Larry Hill Live Reporter Join Date: Oct 2004 Location: Hickory, Ky Posts: 10,633 Likes: 1,927 Liked 10,687 Times in 2,225 Posts	Re: Connecting Rod Clearances So what did you do? __________________ IHM Used Parts https://ihmusedparts.com 888-821-1817

06-26-2017, 09:21 PM	#8
jrstock Junior Member Join Date: Feb 2015 Posts: 16 Likes: 0 Liked 0 Times in 0 Posts	Re: Connecting Rod Clearances Follow Up I found on a past classracer post that is very difficult to take a few tenths off a connecting rod journal. http://www.classracer.com/classforum...ad.php?t=53273 These were the other options I looked at: 1) Polish connecting rod journal 2) Hone Rod Big End 3) Grind Crank to .040 Under In the end swapped to another crank rather than risking any of the above options. Thanks for the advice!