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Location: Canberra Australia
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New Deck Height Question!

Hi,

I have searched the board and ready all the posts with anything related to deck height in them..........nothing like my setup.

3.0 SC 79
JE 10.5:1
GE80
V Max springs
Twin Plug
SSI
Monty
ARP Bod Bolts
7,500 red line.

Ok I have assembled the bottom end and have started to look at the deck height. Using the solder method I get a reading of 1.51
avg on Cyl #1 and 1.48 avg on cyl #4.

The strange thing is that the solder is not flat at the end. It has a thicker end on it. The above measurments are taken after the bulge at a crease line. The bulge measures from 1.96 to 2.16. It also appears that the solder is thinner moving towards the top of the piston. ie 1.38 to 1.42 on a piece of solder 1 cm long.

I am just about to lay a complete piece across the piston and recheck to confirm this.

So the question is! Is the bulge at eth edge of the solder normal?

Any thoughts would be very much appreciated.
Old 09-12-2005, 05:18 AM
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I would be concerned with this bulge. This will probably cause problems when the combustion gases get trapped in this area. The gap between the piston and head should diverge slightly as you go toward the center of the piston so that the mixture is pushed to the center.
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Old 09-12-2005, 05:52 AM
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Mark

Except for the cams, your motor and the one I just finished are very similar. I struggled with deck ht and compression as well. Check out my detailed posting on this subject.

Advice on Deck Ht, Comp ration and Shims for my 3.0
Old 09-12-2005, 05:20 PM
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tom139racing,

I did read your post and got a lot of information from it. I still need to do the solder right across the piston to see how much room I have.

Even If I have enough room across the head I still need to address the issue of the deck height and the large gap at the very permiter. I don't know if you can run without a base gasket but this would only get me an additional .25mm anyway not enough to drop the larger gap to spec. Even doing this would only decrease the smallest measurment to 1.23.

I am not too worried about the CR until I can get the deck height sorted out. Hopefully I can avoid machining the Cyl and then the head or piston.

This reduild is turning into a nightmare.

Thanks

Mark.....
Old 09-12-2005, 05:32 PM
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Here's some more follow-on to my deck height/Compression saga:
What's Your Head Volume?
Old 09-12-2005, 06:10 PM
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tom139racing,

Now I am concerned that my heads have been altered to accomodate different pistons. The Head to Piston measurement is really important now to determine what work has been done.

I still need to do a compression calculation..........if only I had more time!

Cheers

Mark.......
Old 09-12-2005, 06:30 PM
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Mark

I did lay the solder all the way across the piston dome in one of my measurements and found that the only place the solder was deformed was at the edges next to the cylinder wall. Have you tried this?

I ended up making the deck ht measurement using a digital caliper and a dial gage to ensure TDC. The piston usually has a lip around the circumference that can be used as a base to measure the deck ht to the top of the cylinder edge. I found this method to be more repeatable than the solder.
Old 09-12-2005, 06:49 PM
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Below is the picture of the profile of the head and the Piston. As you can see the gap between the piston and head gets bigger as the head champhers off. The head top piston clearance is ok but it is this outside gap that worries me.

Is the profile of the head normal?

Is the profile of the JE normal?

I am using a .25 base gasket the only way to reduce this is to remove the gasket or machine the cyl. Any suggestins would be appreciated.





Cheers

Mark.....
Old 09-13-2005, 05:16 PM
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Mark

You're way beyond my experience here. I thought that the minimum gap should be at the edge of the piston. You need to have one of the more experienced guys like Chris Bennet or Steve Weiner weigh in on this one.

Have you verified the gap by laying the solder from edge to edge across the pistone dome?
Old 09-13-2005, 05:41 PM
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Tom139racing,

I have just measured the head mating surface. The chamfer starts @ 92mm and extands out to 98mm. I am starting to think that the head has been machined to accept 98 mm barrels to make a 3.2 SS motor.

Does anyone have experience of this?

Thanks

Mark......
Old 09-13-2005, 05:48 PM
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