misaligned sbc deck dowel pins

[nawlins-tim]

I have a fresh short block 400. Got a new set of Profiler heads and went to test fit and BOTH heads won't fit correctly over the left bank dowel pins. Its not much but the heads won't go on without a pounding. Anyone ever have this problem? I can't notice any mushrooming of the pins either. trying to decide what is the fix. Also the block was decked and squared.

 

[grumpyvette]

What he ^^^^^ said. SMALL blocks use small "pins" similar to (if not exactly the same as) what is used to locate the timing cover.

Cylinder Head Dowels, .316 in. Outside Diameter, .629 in. Height, Chevy/Mopar, Pair
Mr. Gasket 4375

BIG blocks use HOLLOW alignment dowels, they fit around a head bolt on each end of the head.

Cylinder Head Dowels, .646 in. Outside Diameter, .503 in. Height, Chevy, Big Block, Pair
Mr. Gasket 4377

Or if you want to move the head around on the cylinder bores

Cylinder Head Dowels, Offset, .030 in. Chevy, Big Block, Chrysler Big Block, Set of 4
Moroso 37900

most machine shops will gladly sell you, or can easily order you and sell you ,off set center,cylinder head too block deck dowel alignment pins designed to correct this rather common issue

 

[87vette81big]

I never had this problem on Pontiac & Olds engines Grumpy.
But have seen it on a few SBC's.

 

[nawlins-tim]

Yeah I knew about the offset dowel's but it would be a guestimate of how much offset will work. And then there is taking the old one's out, urgh. I know the machine shop owner that I use will just tell me " welcome to the aftermarket engine building process."

 

[87vette81big]

Yeah I knew about the offset dowel's but it would be a guestimate of how much offset will work. And then there is taking the old one's out, urgh. I know the machine shop owner that I use will just tell me " welcome to the aftermarket engine building process."

It can be measured the offset required.
Need the right measuring tools.
Wait For Grumpy again to advise.

 

[grumpyvette]

mark the top of the existing index pins with machinist blue (DYE) center the cylinder head hole of the existing cylinder head on one hole like it would normally seat on the index pins and set it down as close to the correct location as you can get it, then grab your calipers and measure the thickness of the offset mis- match blue marking,the tip of the dye marked pin made as it marked the head, lets say its .032 offset, well that would indicate both pins need a .016 offset , or one or both pins need a .032 offset , depending on what direction your trying to move the head obviously, keep in mind that the cylinder bore center-line and the valve center-line may not be the same and keeping them similar will increase the potential air flow rates,
you might have somehow gotten the IN-CORRECT idea that the valve center-line and CYLINDER center-line are exactly matched in a sbc, they are NOT!
plus the valves are angled at a 23 degree angle so the outer valve edges close to the cylinder walls do not drop strait down into the bore as the valves open at the point of the cylinders largest diam. moving the head center-line to move the valve center- line to maximize flow at max valve lift potentially helps performance.
(keep in mind moving the heads around also has a minor effect on the intake manifold fitting and gasket sealing,minor changes usually have little effect, and usually don,t have a huge effect on valve train geometry, issues , so don,t get carried away with this as some magic cure for increasing air flow or un-surrounding valves, because it can cause problems if you push limits, check everything, don,t assume after changes everything bolts up and flys without checking)

http://www.highlandwoodworking.com/star ... ye4oz.aspx

http://www.hardwarestore.com/machinist- ... 54090.aspx


http://loctitefreezeandrelease.com/

AFTER a 10 second spray with freeze spray and a good firm grip and rocking motion, 10" nippers pull those index pins out of the block with ease,, btw once used,and if they get pulled out, those pins get pitched in dumpster, as a one time use, item, and get new replacements, as once they are pulled out,they distort, are cheap and get burred easily, so get replaced

 

[nawlins-tim]

Well FIRSt I want to say thanks for responding so quickly ( Grumpy & others ). Anyway the problem seemed so small I figured I would sand and file the dowel pin first. And that is what I did. After a few tries, the head went on. The whole ordeal was less of an issue than I thought. I just wanted to be careful.
Now I just have to check the piston to valve clearance( clay test ), then on to pushrod measurement. But meanwhile I'll be looking out for some kind of misalignment that was triggered by the dowel pin ordeal .