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| Why do I keep breaking pistons??? https://www.slantsix.org/forum/viewtopic.php?t=67395 |
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| Author: | Daddiojoe [ Sat Sep 02, 2023 12:05 pm ] |
| Post subject: | Why do I keep breaking pistons??? |
Piston Breakage #1-- 71 D100 propane powered. Hole in #3 piston after driving 60-70 on country roads. 3:23 rear. 727 trans. Piston Breakage #2--same truck but now gasoline. Shattered piston #4 on highway after less than 30 minutes. Driving 50-60 mph. Piston Breakage #3--64 Valiant wagon. Chipped off ring land on piston #1. Did some highway travel, but generally under 60. Car ran hot for 10-15 minutes (over 200 degrees). 3:23 Sure Grip rear w/ 904 transmission. All engines are set at initial timing of between 8-10 degrees BTDC. Gas powered truck and Valiant using Carter BBD. Most recent breakage was confirmed today after removing the cylinder head. I am a fan of slant sixes, but what's up w/ the problems I am having with this "indestructible engine"? Ideas appreciated. |
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| Author: | Rick Covalt [ Sat Sep 02, 2023 1:19 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
How miles was on each engine? Is it possible the first hole was due to a very lean condition with the propane set up? And could the second one be related back to that? Sorry I am only guessing. |
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| Author: | Charrlie_S [ Sat Sep 02, 2023 1:20 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
Any chance you could show some pictures of the pistons? What compression ratio? Sounds like it might be detonation. |
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| Author: | volaredon [ Sat Sep 02, 2023 4:22 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
I wouldn't call 200* "hot". |
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| Author: | Greg Ondayko [ Sat Sep 02, 2023 5:33 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
Are these oe pistons in a not-rebuilt short block or new pistons in a fresh rebuild(s)? Greg |
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| Author: | slantzilla [ Sat Sep 02, 2023 6:03 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
How much advance total with the vacuum added? Sure sounds like detonation. |
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| Author: | DadTruck [ Sat Sep 02, 2023 8:58 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
Shattered piston, chipped ring groove,,, Could also be improperly gapped rings, Photos are needed. |
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| Author: | Daddiojoe [ Mon Sep 04, 2023 11:22 am ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
I never got around to checking total advance, just initial, which was 8-10 degrees BTDC. Compression ratio on the truck was estimated at 9.5:1 by the shop that rebuilt the heads. Compression ration on the Valiant is unknown. First breakage on the truck--approx 5,000 miles on rebuilt engine. Second breakage on the truck--less than 1,000 miles on same engine rebuilt. Mileage on Valiant engine is unknown. When the truck was powere by propane it had a computer to maintain air/fuel ratio. Impco components. I am planning to put the engine I had rebuilt for the truck in the Valiant. Several cylinders needed to be re-sleeved after the piston shattered. That leaves me with the truck. I am considering a 318 for it. Would like to read advice from folks running /6 in their trucks. I am out in the country and need to be able to consistently drive highway speeds. |
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| Author: | SlantSixDan [ Mon Sep 04, 2023 11:56 am ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
Quote: First breakage on the truck--approx 5,000 miles on rebuilt engine. Who chose and supplied the pistons?Second breakage on the truck--less than 1,000 miles on same engine rebuilt. Quote: I am considering a 318 for it. A properly-specced and -built 318 is a fine engine. So is a properly-specced and -built 225. Bazillions of them were made; most of them didn't and don't break pistons. The problem is not with the design of the Slant-6 or its pistons; somebody on your end is doing something wrong (or having extraordinarily bad luck, or pissed off the wrong deity, or did some very bad piston-related thing in a past life).
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| Author: | Greg Ondayko [ Mon Sep 04, 2023 12:55 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
Who is rebuilding the engines? You or are you having a shop do the work? If shop did the same shop build all of the engines with the broken pistons? |
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| Author: | Daddiojoe [ Mon Sep 04, 2023 1:05 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
Greg and Dan-- Thanks for your comments. I like the idea that I just pissed off the piston gods, Dan. I almost always make a blood sacrifice when working on anything significant, though. Different shops for all three occasions. As far as I know all six pistons were new in each case. I paid for new pistons, anyways. First time truck--shop in Austin, TX Second time truck--independent rebuilder in Austin Valiant--no idea. I rescued the wagon out of a wrecking yard. All three times only one piston had problems and others looked okay. |
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| Author: | Dart270 [ Tue Sep 05, 2023 3:58 am ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
It is most likely either detonation from too much timing under load (initial timing has nothing to do with hurting engines/pistons), OR lean mixture causing detonation. Yes, it has nothing to do with the design of the engine. It is also possible that bad machining or assembly is causing this. All of this said above, just emphasizing... Lou |
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| Author: | Greg Ondayko [ Tue Sep 05, 2023 5:01 am ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
I have never seen anyone break stock na pistons in normal use. I have seen them break under boost or with nitrous. I am sure it happens due to the above mentioned issues. Greg |
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| Author: | Daddiojoe [ Tue Sep 05, 2023 2:13 pm ] |
| Post subject: | Re: Why do I keep breaking pistons??? |
OK. Thanks for your insights, everybody. Joe |
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