Checking for decked block on 327

[Michael W.]

Re: Checking for decked block on 327

Possibly another clue would be the similarity of the left hand deck surface finish to the right hand. I don't think the rebroachers would do both sides, nor would they make great efforts to match left to right.

Most untouched blocks I've seen have similar left/right broaching marks.

[Michael G.]

Re: Checking for decked block on 327

I didn't look at the broach marks with a scope, but both banks looked similar to the naked eye. I do look at a lot of surface finishes in my business , so while not an expert, I can usually distinguish between different types of surface.

The heads were off when I saw it, Duke. By "deck clearance" are you referring to the distance between the flat surface of the piston-top and the deck surface?

Mike

[Joe C.]

Re: Checking for decked block on 327

I didn't look at the broach marks with a scope, but both banks looked similar to the naked eye. I do look at a lot of surface finishes in my business , so while not an expert, I can usually distinguish between different types of surface.

The heads were off when I saw it, Duke. By "deck clearance" are you referring to the distance between the flat surface of the piston-top and the deck surface?

Mike

Yes........to the crown, not the flat top of the dome (if it has one). On a domed piston, the crown is measured as the machined, outer flat annulus on the piston top.
If you are using a single depth gauge, then take two measurements, equidistant on both sides of the piston center, at the inboard edge and the outboard edge, and then take the average of the two measurements. Rock the piston through TDC to be sure you are exactly at TDC.

[Michael G.]

Re: Checking for decked block on 327

Thanks, Joe,

What is the expected nominal deck clearance on a production 327-360 engine?

Mike

[Duke W.]

Re: Checking for decked block on 327

Nominal piston compression height for all OE 327 pistons is 1.675". Add the 5.700" nominal rod center to center distance and 1.625" crank throw radius and the sum is 9.000".

So nominal deck clearance is.... (a seventh grade decimal arithmatic problem).

Duke

[Joe C.]

Re: Checking for decked block on 327

Nominal piston compression height for all OE 327 pistons is 1.675". Add the 5.700" nominal rod center to center distance and 1.625" crank throw radius and the sum is 9.000".

So nominal deck clearance is.... (a seventh grade decimal arithmatic problem).

Duke

Duke,

I went to Catholic school................so it might have been sixth grade. Or, was it eighth grade? I don't remember.
Anyways, my abacus figures it @ .025", plus/minus 2" ()

[Michael G.]

Re: Checking for decked block on 327

Thanks guys, I think my 5th grade son did that math a couple years ago. I thought it might involve triple integrals and other stuff I forgot by my senior year at U of M.

Mike

[Tom L.]

Re: Checking for decked block on 327

I teach 7th grade, believe me it isn't as easy as you think!

And by the way, dividing 3/4" by 2 is advanced calculus to them!

[Michael H.]

Re: Checking for decked block on 327

I teach 7th grade, believe me it isn't as easy as you think!

And by the way, dividing 3/4" by 2 is advanced calculus to them!

Nah, it's easy. 3 and 4 = 7. Half of 7 is 3 1/2.

I always thought a typical mid 60's small block deck dim was 9.020"? Pistons down in the hole about .010"-.020".

[Tom L.]

Re: Checking for decked block on 327

Congradulations!!! You made it to the eigth grade!!!

[Duke W.]

Re: Checking for decked block on 327

Nah, it's easy. 3 and 4 = 7. Half of 7 is 3 1/2.

I always thought a typical mid 60's small block deck dim was 9.020"? Pistons down in the hole about .010"-.020".

On recent 327 restoration projects I've been involved with the least deck clearance was about .025" - the nominal dimension - to about .040", and there was as much as .010" right to left difference. IIRC the rod center to center distance tolerance is +/- .002" and I think piston compression height and crank throw radius tolerance is even tighter, so most variation in deck clearance is due to deck height variation.

So based on the data I have, most decks are nominal to high. I've not run across a Flint machined block that had less than .025" deck clearance with OE compression height pistons.

I rant and rave about measuring deck clearance prior to teardown and again during assembly. Once final deck clearances are known you select a head gasket thickness to achieve the target CR, and if there is more than about .005" side to side difference, you can usually find different thickness head gaskets to minimize final side to side CR variation.

If you don't do this you have no idea what the real CR numbers are because about .010" difference in deck clearance or gasket thickness is nearly half a point!

Duke

[Michael H.]

Re: Checking for decked block on 327

On recent 327 restoration projects I've been involved with the least deck clearance was about .025" - the nominal dimension - to about .040",
Duke

Yeah, you're probably right. It's been 35 years since I was building a lot of race engines. Maybe I remember the 9.020" as a target for a correctly decked block with steel head gaskets? Total of .035" min piston to head. (.050" with aluminum rods)

[Joe C.]

Re: Checking for decked block on 327

Yeah, you're probably right. It's been 35 years since I was building a lot of race engines. Maybe I remember the 9.020" as a target for a correctly decked block with steel head gaskets? Total of .035" min piston to head. (.050" with aluminum rods)

I just built mine with pistons .004" - .006" out the hole, used Mr Gasket 5800 (.038" compressed). Reason for the piston-to-deck clearance variation, is that 4 throws were measured @ 1.625", and 4 were measured @ 1.627" (crank throws were, indeed plus .002 on 2 journals...................so I have a "semi-stroker" ). Crower Sportsmans seem to keep the pistons from hitting my 64.7 - 65.2cc chambers. All non-machined areas on the Speed Pro L2166NF-30 pistons' crowns (rough cast within the machined annulus) were filed flat to match machined annulus. Some of those raised areas were, in fact, .004" higher than the "nominal" crown dimension.........so anyone building a tight quench engine, be aware of this if you are using the el cheapo Speed Pro buckets.

[Duke W.]

Re: Checking for decked block on 327

I just built mine with pistons .004" - .006" out the hole, used Mr Gasket 5800 (.038" compressed). Reason for the piston-to-deck clearance variation, is that 4 throws were measured @ 3.250", and 4 were measured @ 3.252" (crank throws were, indeed plus .002 on 2 journals...................so I have a "semi-stroker" ). Crower Sportsmans seem to keep the pistons from hitting my 64.7 - 65.2cc chambers. All non-machined areas on the Speed Pro L2166NF-30 pistons' crowns (rough cast within the machined annulus) were filed flat to match machined annulus. Some of those raised areas were, in fact, .004" higher than the "nominal" crown dimension.........so anyone building a tight quench engine, be aware of this if you are using the el cheapo Speed Pro buckets.

You're confusing stroke with crank throw radius. Crank throw radius is half the stroke, so if stroke is 3.252", then the throw radius is only .001" high.

On a typical engine if you see +/- a thou or two random variation along a deck with no indication of tilt, you've got a straight block and good rotating/reciprocating assembly. It doesn't do much good to get it tighter than that - even on a racing engine where you are usually looking for maximum CR.

Duke

[Duke W.]

Re: Checking for decked block on 327

Yeah, you're probably right. It's been 35 years since I was building a lot of race engines. Maybe I remember the 9.020" as a target for a correctly decked block with steel head gaskets? Total of .035" min piston to head. (.050" with aluminum rods)

On a racing engine it's typical to take a "cleanup cut" to equalize both sides and eliminate any "tilt" - although I think "tilt" is a lot less common that most guys think, but .005" side to side difference is not uncommon. If the lowest deck is 9.025", then it makes sense to take .005" off that side and whatever is necessary to make the other side 9.020".

Duke