421 Deckheight

[J-Madd]

Locked up a 421 Cub (68mm x 58mm, 115mm rod) and having it ported but I need to know if it is zero deck with the recommended 0.012'' base gasket and Blaster pistons. It looked close while it was together, but now it's apart and I was just wanting to get the facts.

 

Edit: Just noticed in the title there is a typo in the base gasket size. Should be 0.012". If a mod wants to fix that for me that would be great. If not don't worry about it.

[locogato11283]

i fixed your title and im moving this to the drag forum. probably get more attention in there.

[J-Madd]

Thanks loco.

[dajogejr]

You can get casting inaccuracies just like you can gasket thickness.

 

I usually start out with two or three gaskets that I measure up the same before I torque the cylinder down so I know I can start off with a level playing field...

 

I like to run .020 on my 10 mil, and I had to run a pair of .012 on my 4 mil since I had to have the deck height resurfaced due to a dip in the middle...

 

Best way to check is get 4 gaskets, two .012 and two .020 and check their thickness first, mock it up with one of each and check your deck height.

It's what I'd do...

[No Limit Powersports]

On a 68x58 a .012 gasket will put you .01 in the hole.

 

Hope this helps

[J-Madd]

0.01'' in the hole is +0.01'' deck, right? Deck is taller than piston at tdc?

 

 

What should the 68x58 Cub cylinder measure in height? I can measure mine and see if it is out of spec at all. The problem is that my crank is pretty much trashed and the motor is apart. In addition, I have had bad luck trying to check the deckheight. I can't eyeball the piston crown and see if it's close. I thought a motor was zero deck and then my engine builder/friend measured and said it was about 0.020" out of the hole!!??

 

I know there are other variables, such as discrepancies in pistons, cranks, rods, cases, etc. I don't know what the tolerance limits are on all of those.

[firebanshee]

Has the bottom of the cylinder been decked to change port timings?

[J-Madd]

Has the bottom of the cylinder been decked to change port timings?

 

 

No. Cylinder is basically untouched except to clean up casting flaws.

[Wildcardracing]

The recommended base gasket as per CP for the longrod 421 is .020-.022 it should measure approximately 4.158" base to deck. Most I have worked with come up with around +.015 deck with a .020 (stock) base gasket thickness. So you will end up with about .007 deck height with a .012 gasket. Some will depend on gasket variances, some will squish more than others when torqued. Blaster pistons have a .105 dome rise, you can use a piston stop and dial indicator to calculate the exact deck height. A piece of strap with two holes drilled and bolted on your studs will work for a piston stop. hope that helps.

[J-Madd]

Thanks, that info will help. Also - where did you get the 0.020" base gasket figure? I know it is common to run that size with the 68x58 Cub, but the website says 0.012". CP Industries

[252wheelieking]

Thanks, that info will help. Also - where did you get the 0.020" base gasket figure? I know it is common to run that size with the 68x58 Cub, but the website says 0.012". CP Industries

 

Can you please answer this brandon, as im interested in learning much as possible about this cub.