Im leaning towards a .060 thick gasket and machining the pistons down .020. I too have the means to do it myself. In theory It should give me .040 quench. Im only finding readily available gaskets in a 4.080 bore.
I THINK I KILLED THE 340
- Thread starter spd691
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Thats why I did the mock up. Cant use clay until I figure out where the heads will sit.
PRH
Well-Known Member
I’d push the easy button with the thicker gaskets.
Standard bore right? Cometic has a .060 thick gasket with 4.040 bore.
Couple things. As mentioned a thicker head gasket could be your answer.
As to your question how much was the block cut. It isn't really the right question.
Your machinist is right that the twisted block would require taking more off one end than the other to bring the deck in parallel to the crank. Likely needed more of one side of the deck than the other as well if twisted.
The real question is what is the new deck height? You need this measured from the crank centerline. I wouldn't assume the guy did anything wrong unless that measurement is off between ends of the same bank or from one bank to another.
I would also want to know why the positive deck height of the pistons was higher on some cylinders than others. Did your machinist assemble the short block or did you? Who measured the rod length and piston compression height? Was the crank indexed? I would suggest swapping a couple piston and rod assemblies from the same side IE the .040 proud one for a .034 proud one to see if that would bring the heights closer together. Entirely possible that tolerance stack of parts could be the difference and not anything that the machinist did wrong.
Another possible solution would be to run a set of the 340 edelbrock heads that have a chamber relief cut.
If you are going to have to cut pistons for valve clearance anyway you might want to shop for pistons instead at that point. Get a newer lighter piston with narrower rings rather than spending money on the old used TRW heavy pistons you have to cut deck height and valve clearance.
I am +.030. 4.070. I see 4.180 but I don't think it takes the chamfer into account.
I assembled it for a mock up (no rings or piston clips installed yet) for checking bearing clearances and piston height. The rods are new. I know they still need to be checked. I am going to do some swapping and rechecking in the next hour. I measured the the piston to deck height myself inline with the pin and checking piston rock. Crank was not indexed. Stock forged. I am assuming based on the difference between the side to side more was taken off one side. I should be able to verify that by swapping some around. I understand production tolerances vary some. I can cut the tops myself at work. The valve relief dims are my bigger concern if I do this. You are correct about different pistons. What I have is time and a bit of knowledge, which is growing by the hour thanks to you guys. Money is the bigger issue if I have to spend I guess Ill have to. I already have the SM closed chambered heads. I was expecting such a large change in height. The reason I had it decked was for a good sealing surface for the new heads. It was a bit rough.
340sFastback
Well-Known Member
Any clue what the deck height is? I would no do nubs without knowing actual deck height.
A LOT
I suspect the intake will need milling and shorter pushrods
Phreakish
Well-Known Member
I'm running MLS gaskets on a used block with new heads and no issues.
I don't know how they spec the bores though. Mine was advertised much smaller than the actual bore of the Gasket measured, so if that's a critical thing for you I'd call the Mfg for specs. If I had to guess, they spec the bore by what the block is bored to, not always what the Gasket measures, but that probably varies by Gasket Mfg too.
I don't know how they spec the bores though. Mine was advertised much smaller than the actual bore of the Gasket measured, so if that's a critical thing for you I'd call the Mfg for specs. If I had to guess, they spec the bore by what the block is bored to, not always what the Gasket measures, but that probably varies by Gasket Mfg too.
Mock it up with the X heads. Are they virgins or have they been ported? I realise you have a set of alloy heads but they obviously won't work with those pistons. Depending on the chamber on the alloy heads, the piston domes may not play well with them anyway. You might be better off with a set of zero deck flat tops with those alum. heads.
Bobzilla
Well-Known Member
If you machine the pistons down .020 and use a .060 thick gasket you lose .020 valve clearance.
If you use an .080 thick gasket and leave the pistons alone you keep that extra .020 of valve clearance in case you need it later.
Both ways end up with same piston to head clearance, and both are equally correct procedures. But thicker gaskets cost about the same as thinner ones, so using the thicker gaskets is cheaper and easier. Both ways need the gasket ordered larger than block bore diameter. A 4.04 bore block uses 4.07 or larger gasket bore. The gaskets are actual size, not correct size for the diameter listed. A 4.04 gasket will likely overhang a 4.04 cylinder bore.
Call these guys and discuss the gaskets. They are a Cometic dealer and will help you get what you need.
FBO Ignition - Home of the HRR688
If money is the primary concern then just optimize what you have for sure. There were a lot of production 340s put out there that are further off speck than what you have.
I'd swap holes with that 040 proud piston and rod combo and see if you can get it close to the rest, get the heads and deck finished for cometic gaskets and let her rip.
So many Reponses, I appreciate it. Here is what I have decided to do. I'm going to machine the pistons down to zero deck, which is the amount above for each piston. This should give me a balanced power stroke for each hole, I would think. Use a MAHLE / CLEVITE 3536SG head gasket which should provide the desired .040 quench I was after. Once I have the bottom end squared away I will call Hughes Engines, give them the specs (car and engine) and see what they recommend for a cam. If V/P clearance is an issue once I choose a cam, I will use Lindy Tools Company Piston Fly Cutters to deal with it. Then balance, after I determine the bob weight needed. I do understand the rotating weight vs reciprocating weight. I did swap the #2 and the #8. No significant change in height. Thoughts?
gzig5
Well-Known Member
Out of curiosity, are your above deck measurements in line with the pin, or worst case tilt at top or bottom of the piston? There isn’t a huge difference, especially on fresh bores but I think I saw a few thou on my worn bores
I was in line with the pin and check by rocking.
mderoy340
Well-Known Member
swapping 2&8 is a no go, the valve relief orientation of int and exh are not the same.
Valve reliefs are symmetrical.
mderoy340
Well-Known Member
my bad, my old trw flat tops are not. My pistons are .022-.025 above deck and I run a .060 thick composite gasket with closed chamber heads for many years.
Im trying to find a .060 composite. seems they are all MLS now. Thats how I really want to do it. How did it run?
mderoy340
Well-Known Member
It runs 11.70s in my 3250 lb street/strip car. MP used to carry .060 composite to drop compression.
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