109 and production 4.1L deck height comparison

[jdpolzin]

I'm building a 291 cast # 4.1 motor for my Regal now. I just got the block back from the machine shop after having new cam bearings installed, turned a turbo crank 10/10, drilled the drainback hole, cleaned the block, balanced the rotating assembly, had the cylinders honed, heads got new valves and seals, etc. I'm going to use a 218/218 Comp flat tappet cam, matching springs, lifters from my buddies 109. He's also got Chromoly push Rods to go with the set. My question is, are the 291 and 109 deck heights the same? I'm thinking the 109 is shorter from what I have read? Can I use the chromoly rods from the 109 or should i use my stock 4.1 rods to be safe? I have a spare set of new 109 pushrods in the garage and they look to be slightly shorter. What do you guys think? ------Jeremy

 

[bison]

The deck heights are different. You have to determine what length pushrod you need. No one can tell you if what you have is the correct length.

 

[gnxtc2]

I would reconsider in using that flat tappet cam.

Billy T.
gnxtc2@aol.com

 

[jdpolzin]

Bison, I know I have a set of stock length pushrods from this 4.1 and the deck was not resurfaced. So, with that said, I suppose I'll just use those. I wasnt sure if the stock deck height were different between 3.8's and 4.1's.

Billy, why would you say not to use a flat tappet? Thats a pretty open statement statement. There are many people using flat tappet cams in all different types of motors in all different types of cars for all different tyes of applications. Please explain.

 

[jdpolzin]

On another note, how do you guys feel about the strength of stock pushrods?

 

[1chance]

I think the deck height is the same, not sure how strong the stock rod are.

 

[earlbrown]

The 4.1 is .025" taller

 

[bison]

Bison, I know I have a set of stock length pushrods from this 4.1 and the deck was not resurfaced. So, with that said, I suppose I'll just use those. I wasnt sure if the stock deck height were different between 3.8's and 4.1's.

Doesnt matter if they came out of a 4.1. You still need to check. Cam base circle could be different.

 

[DR BOOST]

headgasket thickness varies also

 

[turbodave231]

The stock deck height of a 1986-1987 "109" block is 9.522.

Buick lowered the deck height when they changed to composite head gaskets and TTY bolts.

I would not deck an earlier block too much. You need the extra thickness. Earlier block were known to be thin on the decks.

 

[jdpolzin]

Doesnt matter if they came out of a 4.1. You still need to check. Cam base circle could be different.

Do you have a "how to" link to properly check length I will need? Also, as far as headgasket thickness, When someone changes a headgasket with the motor in their car, do you need to re-check pushrod length?

 

[1chance]

The 4.1 is .025" taller

I had no idea, that is why i have a little more valve train niose? Can i grind down the rocker shaft pedistal a little to get them tighter?

 

[pajo]

gizmo

Here is the gizmo you need...FULL THROTTLE SPEED - Pushrod Length checker 7.80-8.80

 

[bison]

Do you have a "how to" link to properly check length I will need? Also, as far as headgasket thickness, When someone changes a headgasket with the motor in their car, do you need to re-check pushrod length?

Only re-check if the gasket is a different compressed thickness and the heads are the same as before.

 

[jdpolzin]

I'm curious as to what extent the valves need to open and close? Is it 100% open and 100% closed? How do you check these?

 

[charlief1]

http://www.turbobuick.com/forums/ge...125-252-compression-distance-deck-height.html

Something for you to read that should help some Jeremy.

 

[DR BOOST]

I'm curious as to what extent the valves need to open and close? Is it 100% open and 100% closed? How do you check these?

they close 100% and they open depending on cam lift and rocker arm ratio.

always check pushrod length whenever the heads, gasket, cam or rockers are changed