Crankshaft To Block Clearance

[snub]

Wondering what a safe clearance is between the crankshaft and the block. In the picture below I have .020" clearance at the spot noted by the arrow. Also wondering what a safe clearance is from the rod big end/ bolt heads to the block. I remember reading it should be at least .060". Does that seem right?

[Cogburn]

Well, It is close enough not many will tell you to run it but ask yourself how is the crank going to get there? People run piston to head clearance down to .035 or so...

I use a cable tie... if a cable tie lives so will the crank.

[Adger Smith]

.060 min I can't tear up my customers stuff because I'm lazy and don't want to grind. Just repaired the counter weight clearance on a 620 BBC that I was re doing for a customer. Previous builder had it @ .045 and with little, very little run time it left witness marks no the pin bosses of the pistons. I've never had problems with .060 on any part that is subject to deflection.

[treyrags]

If you have problems with .060 you have bigger problems. Cracked block or crank, wiped thrust or mains, loose rod bolts.

[Adger Smith]

Treyrags,
That is my point. Less can get by but there is an insurance margin.
You never know when a pushrod will break or a small piece of valve spring will fly around.
I have even see pieces of oil pickups come loose & fly around inside engines.
Just a little more might make the difference.
You also never can tell when a customer might change cranks during the blocks life and most customers are not real good at checking fit. One crank out and another in.. :~0

[CNC BLOCKS]

GM blocks seem to have a clearance issue in that area .050 should give you plenty of clearance.

[racear2865]

Have u noticed something here. Every one has a number they go with. So pick one and go. BUTTT I am with Adger. When you are doing it for a customer, ya better make sure it is good. Why gamble. Some times I will gamble with my stuff, but never with a customer. Let something happen to the engine and let the customer carry it to some one else. guess who will get the blame and it want be the customer. Most all competitors relish the chance to condemn their competition, so why give them a chance on something as simple as this. just a thought that I try to live with.
reed

[Cogburn]

Just for fun I measured the zip tie I use, .055"

[Fordracer347]

One important thing here is parts selection. It often gets overlooked but different brands have totally different clearances built into them. Eagle vs. Scat rods for instance, way easier to fit the scat rods into an engine than eagle.(I don't like the look of the eagle "stroker clearance" rods that eagle cuts so you don't have to)

Sometimes part selection can be the difference between having clearance and not, its important to match the parts to the application especially if you know its going to be tight to begin with!

[Kevin Johnson]

Nissan rod clearance on OEM louver scraper, SR20: .040"

Dodge V10 clearance on OEM scraper: >.120"

Different design manuals.

[themotorshop]

I have always used .060 as a min, but at that position on crank counter weight I wouldn't expect much flex, so you can probably consider .045 safe, were if it was a center counter weight I would definetly go .060