Author Topic: Clearancing connecting rod for camshaft clearance - Procedure?  (Read 653 times)

Offline tcoupekyle

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Clearancing connecting rod for camshaft clearance - Procedure?
« on: September 13, 2021, 04:58:51 PM »
I have got all the pieces to this little puzzle, but I am concerned... how do you guys go about clearancing the rods so they do not hit the camshaft.
SBC standard cam height Little M Dart Block
3.75 Stroke Howards Billet Crankshaft
6'' Lightening  Aluminum rods
Crower Small Base Circle Camshaft

I have put the crank and the cam in, timing chain and Rods 1, 2. 
Rod 1 hits the block a little in the pan rail area. No Big deal, a grinder will take care of that no problem.
But Rod 1 and Rod 2 Both hit the cam lobes. (just for fun, I retarded and advanced the cam and it makes contact in any position)

My thinking is to coat the cam lobes with grease.
Rotate until contact, roll the crank back off the cam and mark rod with sharpie. then go to the belt sander and take some off.  Re-assemble and check for clearance. If not enough, repeat until 0.60 clearance is obtained.
Any better ideas? Advice? etc?
Thanks

Offline denverflatheader

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #1 on: September 15, 2021, 07:23:57 AM »
Yes, 0.060 - 0.080 clearance would be good.  Do you have a 6 inch steel I-beam rod you could try versus the 6 inch aluminum.  If the steel I-beam clears the cam, then stack both rods together and do comparison and measurement in the specific conflict area to provide a "visual idea" of how much material you have to remove before you start.  On this type project, it could be helpful to know if you are removing 0.060 or 0.160.  Alan

Offline dusterdave173

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #2 on: September 15, 2021, 06:08:38 PM »
,900 base circle is smaller than Small Base circle and cleared on mine   degreeing cam does matter at that point  measure with a  copper wire of know diameter is how we do it in my shop
I have always had a fascination with fast cars at the expense of more normal character development

Offline tcoupekyle

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #3 on: September 16, 2021, 05:37:26 AM »
Thanks for the answers. I'll say this, as I have not actually degreed the cam I have tried 3 positions on the timing chain set crank gear. In all positions the lobe makes contact.
I like the idea about comparing rods. I ordered a few 6" rods last night to try that.
I'm also not sure if it's a 900 base circle. Cam card only says small base circle.

Cam card also says 4 degrees had been ground into the cam if using lobe center to degree use a 110lsa

Offline tcoupekyle

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #4 on: September 16, 2021, 06:18:24 AM »
Duster Dave. What are you measuring with the copper wire?

Offline crider

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #5 on: September 16, 2021, 03:03:34 PM »
You stick the copper wire between the rod and camshaft to make sure there is enough clearance

Offline tcoupekyle

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #6 on: September 16, 2021, 03:14:11 PM »
Oooh gotcha. Makes perfect sense.

How do you guys go about cutting the rods?

Offline msundstrom

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #7 on: September 16, 2021, 05:42:19 PM »
I like lead solder for checking some clearances

Offline tcoupekyle

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #8 on: September 26, 2021, 02:23:55 PM »
Thanks sincerely all for the help.

I used a rotary file and a belt sander to cut the rods down on 1-2-5-6.
They now all clear the cam.
I still have to go back and check clearance and grind a bit more to achieve the tolerance. But the rods are in and motor just about rotates.
I still have 4-8 hitting the block but I'm way less nervous cutting the block than the rods.
https://photos.app.goo.gl/UPigEf5btnpzezSs6

Thanks again.

Curious tho. Should I cut all the rods like this for balancing purposes?

Offline dusterdave173

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #9 on: September 28, 2021, 05:01:44 AM »
I would not---the amount of weight on aluminum would be next to nothing  Run it
Next cam get a ,900 base circle it will clear better  on most combos, that is why they were invented
I have always had a fascination with fast cars at the expense of more normal character development

Offline tcoupekyle

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Re: Clearancing connecting rod for camshaft clearance - Procedure?
« Reply #10 on: September 28, 2021, 06:09:46 AM »
I thought it was a 900 base circle when I bought the cam. (Hand on face) I've learned a ton on this build and paid allot of "tuition"

Offline tcoupekyle

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