deck height again?

[carrerarsr65]

79sc 3.0 je 10.5 to1 pistons using the solder method getting 1.9-2.1 without base gasket 1.70 this engine has new rebuilt rods from ollies, everything new from bottom up,my ? is am I not torqing the head enough 25ft. should do it ? I talked to walt at CE he says I can get away with some higher numbers than 1.5 , I really don't want to leave anything on the table any thoughts

[tharbert]

Originally Posted by carrerarsr65

(Edited) I have a 79 SC 3.0 with J.E. 10.5:1 pistons. Using the solder method I seem to be getting 1.9-2.1 mm deck height and, without a base gasket, 1.70mm. Ollies rebuilt the rods. Everything else is new from the bottom up. I have been torquing the head bolts to 25 ft·lb.

My question is, is 25 ft·lb enough? I talked to Walt Watson at Competition Engineering and he says I can get away with a higher deck height, say about 1.5mm. I really don't want to leave anything on the table. Any thoughts?...

I think you are mixing some terms here. Deck height clearance is the distance from the top of the piston to the top of the cylinder. That measurement does not include the dome. So, in your picture, if your piston is at TDC, you measure the top of the dome to the top of the cylinder and subtract your dome height. Your spec sheet will have that number. Collective wisdom says 1.25mm to 1.50mm is the target: Deck Height


You seem to be saying you've measured dome-to-valve clearance with the solder method. I want to point out that you have THE expert's word here. I'm not sure what you want to hear. I've read where race engines with closely managed tolerances will go under 2mm for exhaust clearance. If Mr. Watson has given you advice on this, run with it. I'm unclear on how the torque spec fits into the question.

An old discussion about this topic...

Good luck!

[carrerarsr65]

no I am referring to setting of the deck height is what you do before piston to valve clearance, these are totally different operations height is set by bolting head onto cyl. with solder on each side of piston

[snbush67]

You will be fine with the 1.70mm, you will have plenty of clearance, you really have to determin your CR by measuring everything using the burrette and fluid to get accurate CC readings. If you need higher CR then you need to mod the heads, order different pistons, shorten your rods, etc.

I assume you have your heads machined for twin plug? That adds a .5 CC or +/- to your head what else was done?

Most stock 78-79SC heads that have been discussed here are measuring out to 87.5 - 90 CCs.


This thread explains it a little better:

Why is my deck height 2mm and what can I do to reduce it?

[tom1394racing]

I would verify with the head off and vernier. Use a dial indicator to make sure you measure at TDC.

[Eagledriver]

The solder method tells you the clearance between the head and the piston at TDC. It was mistakenly called "deck height" in Waynes book. The deck height is the height of the edge of the piston below the top of the cylinder. It is easiest to measure with a vernier caliper. Measure it at the 3 and 9 positon since the piston will rock in the 6 to 12 axis and affect the measurement.

The deck height should be between 1 and 1.5mm. The way you measured will indicate a greater height because the head has a chamfer around the edge. The solder method will only tell you if you have a safe distance between the top of the piston and the cylinder head, it will not tell you the deck height. You need the deck height for your compression calculations.

-Andy

[carrerarsr65]

I feel I have true understanding of now whats goin on here, time to get the out the verniers thanks guys al from mass