Re: 340 build questions
[Re: Hot 340]
#2953850
08/14/21 08:13 PM
08/14/21 08:13 PM
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Joined: Jan 2003
Posts: 20,173 Park Forest, IL
slantzilla
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 20,173
Park Forest, IL
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I have KB's in my old motor. The thing I found is you need to widen the gap until you think it's way too much, then file a little more. People told me you can't spray them, but they are wrong.
"Everybody funny, now you funny too."
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Re: 340 build questions
[Re: J_BODY]
#2953937
08/15/21 08:46 AM
08/15/21 08:46 AM
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Joined: Jan 2007
Posts: 685 pennsylvania
poboyengineering
mopar
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mopar
Joined: Jan 2007
Posts: 685
pennsylvania
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As to the KB107 pistons, what was the piston-wall clearance? They call for very tight clearance. Did the skirts break?
It may be ugly, but it sure is slow.
Girls comb their hair in rear view mirrors and the boys try to look so hard....
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Re: 340 build questions
[Re: poboyengineering]
#2954116
08/15/21 09:05 PM
08/15/21 09:05 PM
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Joined: Jan 2003
Posts: 6,389 Abilene, Texas
fastmark
OP
master
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OP
master
Joined: Jan 2003
Posts: 6,389
Abilene, Texas
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I have not gotten this motor apart so I can’t tell you the clearances yet. And yes I’ve heard about how careful you have to be with clearances on these pistons. End gaps, skirt clearance, etc. I don’t use cheap pistons. My shop won’t either. I’ve know half dozen of my friends who have tried them and they have failed in some for or another. And you are correct, some shops can’t get anything to work right. This is the fifth motor in a row that I have built that some other shop has done something wrong and the engine has failed. And they are coming from all over. I got a 68 440 in a trade deal the other day. It’s still together. I pulled the valve covers and noticed that the oiling holes on the rockers was install UP! What a shame. My shop was started by an old Super Stock racer who built race motors to keep his race cars going and ended up a really good business. To answer your question, though. The piston broke where the valve relief is cut at the rings. It is cut way to deep, in my opinion, for a hyperutectic piston. They are not meant to be as strong as forged. One good thing. It broke apart in a million tiny pieces instead of staying one big piece and punching a hole in the head. I’ll post a picture from my phone.
And before someone says detonation problems, none of the other pistons showed any signs of that. I thought that at first until I realized that the debris had bounced around through the intake plenum and blasted the pistons that on the same plane of the manifold.
Last edited by fastmark; 08/15/21 09:14 PM.
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Re: 340 build questions
[Re: fastmark]
#2954142
08/16/21 12:00 AM
08/16/21 12:00 AM
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Joined: Feb 2015
Posts: 2,072 CA
crackedback
top fuel
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top fuel
Joined: Feb 2015
Posts: 2,072
CA
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I have not gotten this motor apart so I can’t tell you the clearances yet. And yes I’ve heard about how careful you have to be with clearances on these pistons. End gaps, skirt clearance, etc. I don’t use cheap pistons. My shop won’t either. I’ve know half dozen of my friends who have tried them and they have failed in some for or another. And you are correct, some shops can’t get anything to work right. This is the fifth motor in a row that I have built that some other shop has done something wrong and the engine has failed. And they are coming from all over. I got a 68 440 in a trade deal the other day. It’s still together. I pulled the valve covers and noticed that the oiling holes on the rockers was install UP! What a shame. My shop was started by an old Super Stock racer who built race motors to keep his race cars going and ended up a really good business. To answer your question, though. The piston broke where the valve relief is cut at the rings. It is cut way to deep, in my opinion, for a hyperutectic piston. They are not meant to be as strong as forged. One good thing. It broke apart in a million tiny pieces instead of staying one big piece and punching a hole in the head. I’ll post a picture from my phone.
And before someone says detonation problems, none of the other pistons showed any signs of that. I thought that at first until I realized that the debris had bounced around through the intake plenum and blasted the pistons that on the same plane of the manifold. Yep, not enough ring gap is common cause for that type of failure. It's not cheap pistons, it's poor attention to detail and following instruction. The old .004 per inch of bore doesn't work on KB hypers. Used a bunch of those same pistons and juiced that bejesus out of them with no issues. It's not the piston IMHO.
Last edited by crackedback; 08/16/21 12:01 AM.
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Re: 340 build questions
[Re: crackedback]
#2954251
08/16/21 12:04 PM
08/16/21 12:04 PM
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Joined: Jan 2003
Posts: 6,389 Abilene, Texas
fastmark
OP
master
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OP
master
Joined: Jan 2003
Posts: 6,389
Abilene, Texas
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I have not gotten this motor apart so I can’t tell you the clearances yet. And yes I’ve heard about how careful you have to be with clearances on these pistons. End gaps, skirt clearance, etc. I don’t use cheap pistons. My shop won’t either. I’ve know half dozen of my friends who have tried them and they have failed in some for or another. And you are correct, some shops can’t get anything to work right. This is the fifth motor in a row that I have built that some other shop has done something wrong and the engine has failed. And they are coming from all over. I got a 68 440 in a trade deal the other day. It’s still together. I pulled the valve covers and noticed that the oiling holes on the rockers was install UP! What a shame. My shop was started by an old Super Stock racer who built race motors to keep his race cars going and ended up a really good business. To answer your question, though. The piston broke where the valve relief is cut at the rings. It is cut way to deep, in my opinion, for a hyperutectic piston. They are not meant to be as strong as forged. One good thing. It broke apart in a million tiny pieces instead of staying one big piece and punching a hole in the head. I’ll post a picture from my phone.
And before someone says detonation problems, none of the other pistons showed any signs of that. I thought that at first until I realized that the debris had bounced around through the intake plenum and blasted the pistons that on the same plane of the manifold. Yep, not enough ring gap is common cause for that type of failure. It's not cheap pistons, it's poor attention to detail and following instruction. The old .004 per inch of bore doesn't work on KB hypers. Used a bunch of those same pistons and juiced that bejesus out of them with no issues. It's not the piston IMHO. Again, we’re just guess with our prof. I don’t believe in cheap parts. If I remember correctly, when I bought my headlight relay kit from you, you said you chose to buy better relays because they did not give you trouble. That I respect. Honestly, I don’t know why I even mention these pistons anymore. I get sucked into this debate every time I find one that has failed. It’s almost as bad as the covid vaccine debate. 🙄. Just my humble opinion. I called a major engine builder the other day that is world famous and he agrees with me. He won’t use them either. I’m in good company, I think. Maybe I need to mention politic and religion so I can get this one locked up. Lol.
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Re: 340 build questions
[Re: fastmark]
#2954307
08/16/21 02:35 PM
08/16/21 02:35 PM
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Joined: Feb 2015
Posts: 2,072 CA
crackedback
top fuel
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top fuel
Joined: Feb 2015
Posts: 2,072
CA
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I have not gotten this motor apart so I can’t tell you the clearances yet. And yes I’ve heard about how careful you have to be with clearances on these pistons. End gaps, skirt clearance, etc. I don’t use cheap pistons. My shop won’t either. I’ve know half dozen of my friends who have tried them and they have failed in some for or another. And you are correct, some shops can’t get anything to work right. This is the fifth motor in a row that I have built that some other shop has done something wrong and the engine has failed. And they are coming from all over. I got a 68 440 in a trade deal the other day. It’s still together. I pulled the valve covers and noticed that the oiling holes on the rockers was install UP! What a shame. My shop was started by an old Super Stock racer who built race motors to keep his race cars going and ended up a really good business. To answer your question, though. The piston broke where the valve relief is cut at the rings. It is cut way to deep, in my opinion, for a hyperutectic piston. They are not meant to be as strong as forged. One good thing. It broke apart in a million tiny pieces instead of staying one big piece and punching a hole in the head. I’ll post a picture from my phone.
And before someone says detonation problems, none of the other pistons showed any signs of that. I thought that at first until I realized that the debris had bounced around through the intake plenum and blasted the pistons that on the same plane of the manifold. Yep, not enough ring gap is common cause for that type of failure. It's not cheap pistons, it's poor attention to detail and following instruction. The old .004 per inch of bore doesn't work on KB hypers. Used a bunch of those same pistons and juiced that bejesus out of them with no issues. It's not the piston IMHO. Again, we’re just guess with our prof. I don’t believe in cheap parts. If I remember correctly, when I bought my headlight relay kit from you, you said you chose to buy better relays because they did not give you trouble. That I respect. Yes and the reason is failures on the cheap relays. Never had the issues you've seen on my stuff using those pistons. Don't know the answer for your experience. That piston damage is a classic not enough ring gap issue. Std piston gap 4-4.060 bore .016-.018, KB's need .026-.030 for the same bore. As I say all the time, "Pick your parts, Pay your money." Use what works for you. All good here, hope things go well with what you are working on.
Last edited by crackedback; 08/16/21 02:38 PM.
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Re: 340 build questions
[Re: fastmark]
#2954620
08/17/21 12:09 PM
08/17/21 12:09 PM
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Joined: Jul 2003
Posts: 4,769 Holland MI Ottawa
2boltmain
master
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master
Joined: Jul 2003
Posts: 4,769
Holland MI Ottawa
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I believe the top ring of the KB Hypereutectic piston is placed higher up toward the piston top (Closer to combustion heat) than traditional OEM and other cast replacement pitons. I remember reading how many would use the ring end gap spec for a factory cast piston or aftermarket cast piston on the KBs resulting in not enough gap and thus ring ends butting.
Keep old mopars alive.
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Re: 340 build questions
[Re: slantzilla]
#2954897
08/17/21 10:58 PM
08/17/21 10:58 PM
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Joined: Aug 2019
Posts: 9,434 Super Spudsville
Mr PotatoHead
Half Baked
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Half Baked
Joined: Aug 2019
Posts: 9,434
Super Spudsville
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Are the current pistons below deck and by how much?
I agree on the valve reliefs I just checked a extra KB hyper vs the icon forged for the same basic application and the hyper is about .040 deeper. And with this being a small bore piston im getting a rough approx .040-050 thickness to the land. However I use these KB399 domed in my bracket car with a 150 shot ramped and a top gap of .038 with no issues.
Now the Icon Forged with the same 3.950 bore I spray 250 on ramped with a top gap of .028.
Never an issue with either.
I think you have a lot of options going forward, Id almost look for a proper oem 340 rotating assembly and sell the crank to someone else trying the old school mini stroker trick.
I snapped a few pics of the hyper vs the IC Forged and yes the hyper with the oem ring setup is just middle road over a stock cast but they dont make any high compression 318 cast pistons although even stock cast pistons can last and take some abuse.
This whole ring gap is nuts on the hyper and most just cant force themselves to put a mild motor together with big or bigger then poweradder gaps.
What I find interesting is there is some great lit. out about how big a ring gap can be and still work.
A first hand example I can share is in my youth I took a sd455 and re rung it with a simple hone job, it had .0055 bore taper. I used oem shelf moly rings and it never smoked or burned a drop, think of the gap change with over .005 taper so what the gap would go more then double oem?
None the less the lit, showed a minimal power loss with the bigger gaps, they said 1% over a filed set. This article was in engine builder mag and had info from oem ring makers on what some of the high limits were for some older stuff we use.
I snapped a few pics of the hulking hyper vs the ICF although the Icon is a stroker piston but both a 318-040 bore.
STOP POTATO HATE!
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Re: 340 build questions
[Re: Mr PotatoHead]
#2954898
08/17/21 10:59 PM
08/17/21 10:59 PM
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Joined: Aug 2019
Posts: 9,434 Super Spudsville
Mr PotatoHead
Half Baked
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Half Baked
Joined: Aug 2019
Posts: 9,434
Super Spudsville
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Next to the Forged... why cut the hypers so deep and not the forged? These are both zero deck with a blueprint cut deck height. And they wonder why the hyper will hold so much heat.
STOP POTATO HATE!
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