Author Topic: Carillo rod bearing clearance for cb750  (Read 2031 times)

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Offline frodef2

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Carillo rod bearing clearance for cb750
« on: December 02, 2014, 10:06:13 PM »
I have just started the preparations for some "light" engine assembly, and i have a question about the bearing clearances for carillo rods.

According to the spec sheet that the rods came with http://cp-carrillo.com/LinkClick.aspx?fileticket=aVLyichF4%2Fs%3D&tabid=76, the target clearance for the bearings are 0.001" pr inch of crankshaft pin. This made my target clearance 0.0014".  After measuring the pin diameter with a micrometer and adding it all up with green bearings, i get these clearances.

Rod 1: 0.00142" Rod 2: 0.00126"  Rod 3: 0.00126"  Rod 4:  0.00150"

These values look like they are right in the middle of the approximate clearance value noted in the installation papers.

The installation note did not say anything about the min/max allowable clearance, should i just use the values listed in the workshop manual?




Frode Johansen

(edit: added engine type to the title)



 
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Offline HondaMan

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Re: Carillo rod bearing clearance for cb750
« Reply #1 on: December 02, 2014, 10:28:26 PM »
I have just started the preparations for some "light" engine assembly, and i have a question about the bearing clearances for carillo rods.

According to the spec sheet that the rods came with http://cp-carrillo.com/LinkClick.aspx?fileticket=aVLyichF4%2Fs%3D&tabid=76, the target clearance for the bearings are 0.001" pr inch of crankshaft pin. This made my target clearance 0.0014".  After measuring the pin diameter with a micrometer and adding it all up with green bearings, i get these clearances.

Rod 1: 0.00142" Rod 2: 0.00126"  Rod 3: 0.00126"  Rod 4:  0.00150"

These values look like they are right in the middle of the approximate clearance value noted in the installation papers.

The installation note did not say anything about the min/max allowable clearance, should i just use the values listed in the workshop manual?




Frode Johansen

(edit: added engine type to the title)



 
If you are heading straight for the racetrack, those numbers will be fine (i.e., .0012"-.0016").
However, if you are heading for the street and would like a longer-lasting, better-performing, smoother, cooler-running engine that will take about 500-1000 miles to settle in those bearings to a much better-balanced machine, consider using a little tighter spec. In my experience, starting new bearings with new rods on a used crank works best in the .0010"-.0012" range, if you can get it.

When the clearance reaches about 0.0022" the oil pressure starts to drop and the rings begin to struggle to hold back the extra oil that flings up to the bottom of the pistons. At .0030" the lower ring cannot hold the oil back and it begins burning oil and damaging the 2nd ring from this 'flood' when run to speeds above 7000 RPM. The oil pressure usually drops a lot, to about 30-35 PSI when hot, too. This causes cam wear problems pretty soon.
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Offline Jim F

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Re: Carillo rod bearing clearance for cb750
« Reply #2 on: December 03, 2014, 06:35:49 AM »
I keep mine as close to .0011/.0012 as posible
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1983 GS1100EC Suzuki
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1978 GS750/840 Suzuki

Offline MRieck

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Re: Carillo rod bearing clearance for cb750
« Reply #3 on: December 03, 2014, 08:06:31 AM »
Carrillo's usually have the smallest factory bore. I think .0015 to .0017 is good for rods...mains run tighter. You want to get oil past the bearing to cool it...to tight makes that difficult.
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