Same engine as the Mazda MX6….IIRC Carbon build up exacerbated the issue .
Closed chambers gone bad… that’s a wrap
- Thread starter madhatta360
- Start date
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Had a chance to measure each piston at TDC threw the numbers below, thinking I’m going to run .090 head gasket should get me close to the .040 quench going off the tallest piston. Crazy the numbers are all over the place for pistons that should be .018 above top deck.
Included a bunch of photos of heads and holes giggity! Happy Memorial Day friends.
#2= .045”
#4= .053”
#6= .047”
#8= .040”
#1= .027”
#3= .018”
#5= .025”
#7= .022”
All measurements taken from right below the valve relief slightly off center to not get into “bullet casing” these pistons are annoying for that reason.
Included a bunch of photos of heads and holes giggity! Happy Memorial Day friends.
#2= .045”
#4= .053”
#6= .047”
#8= .040”
#1= .027”
#3= .018”
#5= .025”
#7= .022”
All measurements taken from right below the valve relief slightly off center to not get into “bullet casing” these pistons are annoying for that reason.
Did you find anything in stock that size.
dibbons
Well-Known Member
After clean-up deck re-surface, my 340 block was still way uneven when measuring deck height left bank vs right bank. The machine shop told me to run two different head gaskets thicknesses to even things out between banks (short block still in storage).
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gzig5
Well-Known Member
Seems the two decks are at very different heights. Those numbers aren't even worst case with the piston tilted and at the high point? It is possible the rod lengths are off or crank was ground poorly for some of the variation, but decks are different. When I measured my standard bore (with some wear) '71 340, I was getting mostly 0.026" - 0.032" above deck but that was at max tilt. They are a few thousandths less in the middle of the stock pistons. I figured I would need a .065"-0.070" gasket if I put on a set of closed chamber aluminum heads. That may be a moot point now because I think I've decided to have it bored .020 over (.030 if it doesn't clean up), rather than re-ring and send it. Just a little too much bore taper for my liking after re-hone.
Yeah was wandering if that is an option to run 2 different thickness HG for each side since they are way out of whack
Nothing, found something in the .080 on summit with a 4.1” bore so looks like custom head gaskets for me
Others have run two head gaskets stacked together to get the needed thickness. Different thickness gaskets can be used on each side.
If you use either method you will have to double check your pushrod length.
None of this is ideal but short of tearing down your short block it may be your only crutch.
Another thought is to measure the combustion chamber depth of your heads to see if one is deeper than the other. Also may be able to mill the chambers on one head a little deeper.
If this wasn't my daily driver, I would forget all of the above and have the high side pistons milled, or start over decking the block and buying new pistons.
If you use either method you will have to double check your pushrod length.
None of this is ideal but short of tearing down your short block it may be your only crutch.
Another thought is to measure the combustion chamber depth of your heads to see if one is deeper than the other. Also may be able to mill the chambers on one head a little deeper.
If this wasn't my daily driver, I would forget all of the above and have the high side pistons milled, or start over decking the block and buying new pistons.
Yeah that’s what is tuff right now, I’m in a position financially to tackle this however I want to which I’m grateful for but I also would like to enjoy the car for summer. Im all for plucking the motor and sending it out to do a stroker but I know I’d be shocked to have it on the road by august. The gaskets are my short term option but if I need customs ones who knows what lead time is for something like that. This whole build has been a struggle haha ideally I’d like to get it close for now and drive it and then pull the motor over winter and have the entire assembly redone and new cam etc.
Wow that’s interesting a .053 and .039 would get me close one side and for the other the .060 would work, that’s definitely a thought. I’m reluctant to go with Cometic because of the multi layered steel and needing such a smooth/flat surface for sealing purpose.
Something to consider here thanks for the tip. If you stack the gaskets do guys copper spray the 2 together for extra sealing?
Getting the crankshaft indexed and the block decked correctly will solve those differences.
Yah I spoke with Mike at B3 today leaning towards having him do my rebuild and saying screw it let’s make it a fresh build
It'll surely run and probably run well without all that done, but it WILL make a difference to get it all right. .......and now's the time, ain't it? lol
1WildRT
Well-Known Member
Break out the router, then finish with the belt sander..... Wait, wrong thread...
If you have the money do it right then do it and don't look back. It is already too late to enjoy it this summer for the most part if you have someone doing a custom build.
famous bob
mopar misfit
Or , u could use a bandsaw !!!!!!!!! LOL
You guys are missing the easiest way. Fire up the grinder with some 36 grit and lop the top right off those suckers.
At 67 years old I’m not going to tell you guys some of the “tricks” we pulled back in the 1970’s to make a race. We didn’t have many tools so our options were crude and limited. Lol
MOPAROFFICIAL
Oogliboogli
Just look at one through seven there's a .005 variance end to end/front to back, but you have .009 on #3 and then .002 on #5 and .005 on # 7
Sure the deck is probably off .005 end to end and maybe. 009 bank to bank...but the rods are probably up to .010 or .020 variance in length.
.......The rods are different lengths....
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