Best way to measure con rod clearance?

[Drewster]

What's the best way to measure connecting rod bearing clearance.
Do you assemble con rods with the bearing shell in them to measure the ID. or.
Do you measure each rod bearing shell alone on the table top and do the math?

Andrew


86 T-type modified
86 T-type. Lightly modified

 

[KevinB]

bearings installed in the rod and the rod caps torqued to proper spec

 

[Drewster]

Oh good that's they way I'm doing it now but I was having trouble with my stretch gauge on my rods with shop vise



86 T-type modified
86 T-type. Lightly modified

 

[earlbrown]

First, torque up the rods without bearing shells. Then measure clearances on both sides of the parting line, then measure vertical clearance.

Next, hand lap the cap until the vertical clearance is down to round or a maximum of 2.3745" (minimum of 2.3738")

When the hole is to your satisfaction (giggity) break the rods down, dress the parting line with a fine file and retorque with clean deburred bearings.

Set a mic on the exact crank journal they rod is going to live on and use that one to set the bore gauge. If the rods aren't married to a bore yet, measures all 6 rods and marry the largest bores with the largest crank journals.

Steal underpants

?????

PROFIT!!

 

[dr_frankenstein]

First, torque up the rods without bearing shells. Then measure clearances on both sides of the parting line, then measure vertical clearance.

Next, hand lap the cap until the vertical clearance is down to round or a maximum of 2.3745" (minimum of 2.3738")

When the hole is to your satisfaction (giggity) break the rods down, dress the parting line with a fine file and retorque with clean deburred bearings.

Set a mic on the exact crank journal they rod is going to live on and use that one to set the bore gauge. If the rods aren't married to a bore yet, measures all 6 rods and marry the largest bores with the largest crank journals.

Steal underpants

?????

PROFIT!!

somebody been round that block before!

 

[QwikStop]

First, torque up the rods without bearing shells. Then measure clearances on both sides of the parting line, then measure vertical clearance.

Next, hand lap the cap until the vertical clearance is down to round or a maximum of 2.3745" (minimum of 2.3738")

When the hole is to your satisfaction (giggity) break the rods down, dress the parting line with a fine file and retorque with clean deburred bearings.

Set a mic on the exact crank journal they rod is going to live on and use that one to set the bore gauge. If the rods aren't married to a bore yet, measures all 6 rods and marry the largest bores with the largest crank journals.

Steal underpants

?????

PROFIT!!

If your rods are machined by a good automotive machinist then the Big ends should all be within proper spec. I worked as a Machinist and this is basicly how its done, we always sized each rod to a journal, piston to a cylinder and so on, you might want to jot things down for later reference if needed, this is part of a Blue printing process as they say

 

[earlbrown]

The OP didn't mention verifying a machining process. The way I read it, used rods needed to be put in service and clearances verified.

My experience tells me they will most likely be a little egg shaped and tall across the vertical centerline.

 

[Drewster]

I'm using new Molnar rods and working on getting a final reading for the crank when I get it cut 10 under.


86 T-type modified
86 T-type. Lightly modified

 

[turbodave231]

Number your new rods and put the new bearings in place.
Torque the rod bolts to spec using the specified lube.
Set a micrometer to the journal size (for that cylinder).
Then use the micrometer to set a precision dial bore gauge (.0001 resolution).
Measure the rod bearing for that cylinder.
The measurement should always be taken 90 degrees to the parting line of the bearing.
The dial bore gauge will read out the clearance directly when set to the journal size.

Don't have a dial bore gauge and micrometer? Beg, borrow or buy some. Telescoping gauges (T-gauges) suck and are not repeatable IMO. Plastigauge is only an approximation, but will work in a pinch. No respectable engine builder will set bearing clearance without using precision dial bore gauges.

 

[turbodave231]

I re-read your original post and need to adjust the procedure above:

You are having your crank ground undersize, Set the mike to 2.2387 to 2.2395 (2.2487-2.2495 minus the .010)
Then use the micrometer to set the bore gauge.
Adjust the number you use above (within the tolerance) to get the desired clearance

Decide on ONE number that will work on all the rods journals ( or your crank grinder will HATE you or ignore your numbers and do what he wants)

CAUTION: You want to be SURE your micrometer is 100% calibrated and DEAD NUTS accurate if you use this procedure. Check it twice against the Standard provided with the micrometer.

Good Luck on the build.....post some pictures.
Dave

 

[Drewster]

Thank you for the info. You guys are a big help!
Andrew


86 T-type modified
86 T-type. Lightly modified