Trim for big cam

[Dusty1]

How much will I need to trim my lifter bosses for a big cam, say an FK8?

Or:

How much lift can I run before I need clearance?

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[Glenn]

You don't need to trim the lifter boss, but you do have to clearance the cam for the connecting rods.
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[Teeroy]

You may need to trim lifter bores if you have a large base circle cam or thick lifter heads (need to check the parts your using even stock cam), but as Glenn said has nothing to do with cam lift.
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[modok]

It depends on the base circle of the cam and what lifters you use.
Has not much to do with the actual cam grind.
I've never needed to get additional clearance, probably because I use the cb lightweight lifters mainly.

[modok]

But anyway far as how much clearance you need, IMO the valve spring is the limit stop, the spring should bind before the lifter hits the case or the retainer hits the guide.

[bedlamite]

since you're putting a cam in anyway, you could just measure how much clearance you have ...

[Brian_e]

With the right parts selected, an 82m crank will go together with almost zero extra work on anything. At most, you might need to buff the very corners off the connecting rod caps to clear the cam. I do this quick on the belt sander.

For the lifter clearance, you will have the most trouble with the Engle lifters. Big ol' muffin top on those, and they weight a ton. CB lightweights, and TP lifters have a mile of room.

Brian
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[BFB]

[SBD]

I've got an Engle W120 with CB lightweight lifters in an AS41 case and I'm going to have to trim every one of my lifter bosses. The only way to be sure is to check.
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[Dusty1]

[Clatter]

There is variation in cases, cams and lifters.

You will only know if you need to trim the lifter bosses or not if you check them.

Don’t assume anything. Measure.
Trusting some dudes on the forum is folly no matter how smart they might be!

IIRC you want at least .060 clearance.
Might be remembering that number wrong.
Check that too!
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[SBD]

I've read one source that said you need .040" and another that said .050". Not sure what's correct but mine are way less than .030", IIRC.
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[txoval]

.040

Hard to imagine a FK8 needs lifter bore clearancing or any ratio rocker cam for that matter.

Still have to check, but I’ve only run into that with a W125 and thick head Engle lifters.

Easy job with Berg tool

[Dusty1]

I was lookin' for a Flat Earth Society Line In The Sand, a number that if not exceeded is the "go" number, more than that "no go". I reckon it's around .400 cam lift with Engle Fathead lifters as mentioned. The FK8 has .382 cam lift, close enough. The FK89 has .416.

The .060 clearance is a handy number, call it 1/16. Anything over zero is good.

"Why did I break my lifter bosses?"


There are all sorts of details I never had to concern myself with in stock or near stock rebuilds.

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[SBD]

[modok]

I've heard .040 and .060
But I just go by my own logic

[txoval]

Take your time, low pressure.

It will cut fast…last thing you want is .200 clearance

[SBD]