A head piston question

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A head piston question

Post  tfsbbf466 on Sun 5 Apr 2015 - 11:18

I bought a set of old Motorsport A heads and a shortblock that went with it. It has 3 hurt pistons but when I pulled one to send it out to JE and have it duplicated I noticed what looks like the exhaust valve contacted the pistons. Its a flat top with only 1 relief. Are these normal A head Pistons or no? I'm already buying a crank since this came with an offset ground stock crank but if it needs pistons too I may as well go bigger.

If that's the case is there any issues with running a 4.5 cranks and 6.8 rod with a diamond piston? This will be a pump gas street/strip motor with a solid flat tappet cam for now. Will see nitrous use as well.

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Re: A head piston question

Post  cool40 on Sun 5 Apr 2015 - 11:41

If you need 3 pistons anyway buy a new set. You're already buying a crank so go 4.5 with 6.7 or 6.8 rod and diamond can hook you up with a piston for your application. cyclops i have a set of flat top j&e pistons and they have 2 valve reliefs best i can recall.
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Re: A head piston question

Post  tfsbbf466 on Sun 5 Apr 2015 - 13:56



Here is a pic of the piston. I'm trying to build this motor using most of what I have. I may reuse the crank too but feel a forged crank would be better.

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Re: A head piston question

Post  Lem Evans on Sun 5 Apr 2015 - 13:57

The A460 style pistons should have an exh. valve relief.

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Re: A head piston question

Post  dirt_worker on Sun 5 Apr 2015 - 14:41

I noticed that it made contact in more than one spot. Something musta came apart for it to contact again that far apart...
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Re: A head piston question

Post  Lem Evans on Sun 5 Apr 2015 - 15:23

It does appear that the spring had loss control of the valve at some point. Smile

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Re: A head piston question

Post  tfsbbf466 on Sun 5 Apr 2015 - 16:19

Yeah I'm not sure but all of the pistons have similar marks. I had the heads freshened up and all the valves are good. It has a solid roller in it but I'm going with a custom ground flat tappet for this combo. I have bigger plans for the future.

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Re: A head piston question

Post  dirt_worker on Sun 5 Apr 2015 - 16:27

Hmmm....im wondering if you couldnt just put a small exh notch in em and touch up the remaining knicks and run them. I cant find a photo of mine but i from my memory the exh notch on them was pretty tiny.
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Re: A head piston question

Post  Lem Evans on Sun 5 Apr 2015 - 16:43

It'd depend on how much the heads have been milled but, .060" deep should take care of most needs.

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Re: A head piston question

Post  dirt_worker on Sun 5 Apr 2015 - 17:00

i realize this is kinda of a loaded question Lem, but am i wrong in thinking they might still be usable if theyre checked over really well and w. a new notch cut in them?
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Re: A head piston question

Post  Lem Evans on Sun 5 Apr 2015 - 17:11

They could be milled and used but, being that he needs 3 pistons + paying to cut the other five I'm not sure it'll be worth it. Also the new pistons could be of a different wt. which would be a pain.
If he does the 4.5" crank it really won't matter anyway.

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Re: A head piston question

Post  dirt_worker on Sun 5 Apr 2015 - 17:15

All completly valid points that i HADNT considered before posting...THANKS Embarassed
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Re: A head piston question

Post  Lem Evans on Sun 5 Apr 2015 - 17:46


"If that's the case is there any issues with running a 4.5 cranks and 6.8 rod with a diamond piston?"

4.5" with the 6.800" rods is typical.

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Re: A head piston question

Post  tfsbbf466 on Sun 5 Apr 2015 - 19:31

Lem Evans wrote:
"If that's the case is there any issues with running a 4.5 cranks and 6.8 rod with a diamond piston?"

4.5" with the 6.800" rods is typical.
Do you see any issues with longevity for a truck that sees a lot of street use? Trying to get the best of both worlds here lol. How much power can you see me making with a 11:1 557 and a custom solid ft cam? Heads didn't flow all that great imo. Peaked at 393in 340ex. Guy that flowed them said his bench is conservative on the intake (15 low) and generous on the exhaust (+10) I want a nice improvement Over my current TFS street headed 512.

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Re: A head piston question

Post  bbf-falcon on Sun 5 Apr 2015 - 19:40

What bore size?

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Re: A head piston question

Post  droppedf100 on Sun 5 Apr 2015 - 19:58

How fast has the current combo been?


Last edited by droppedf100 on Sun 5 Apr 2015 - 20:30; edited 1 time in total
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Re: A head piston question

Post  tfsbbf466 on Sun 5 Apr 2015 - 20:27

bbf-falcon wrote:What bore size?
4.440

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Re: A head piston question

Post  bbf-falcon on Mon 6 Apr 2015 - 10:24

Same as mine other than c/r.4.500x4.440x6.8. Common deal.

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