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Author Topic:   piston coming apart
leftturn73
Member
posted July 05, 2004 12:13 PM
I belive I have a detonation issue but not sure. I built a motor for a guy and twice he brought it back. 1st time a piece came off the top of #6 piston this time #3 and other pistons are showing signs of bubbling or melting on top. I have verified dampner, distributor and replaced cam. Motor is a 60 over zero deck flat top bottom end 462 double hump -.20 cut and 194/160 valves. The only thing I did not use of mine is my timing light. I set the timeing both times at his garage with his light. should I suspect his light (craftsman dial type) or some thing else.
Thanks


dirtracer76
Member
posted July 05, 2004 07:59 PM
possible detonation, but i would tell the gentleman to purchase a new water temperature gauge.


leftturn73
Member
posted July 05, 2004 08:06 PM
His gauges are new as of this year. I also have been to all but 2 races he has run and he never over heated the motor. All but one night at 190-195. The one night the nose got pushed in and the temp went to 250.


dirtracer76
Member
posted July 05, 2004 08:10 PM
mhm got me


BrianW
Member
posted July 05, 2004 08:32 PM
Have you checked the plugs - i.e. fuel jetting too lean? That would cause the edges of the pistons to pit and 'burn' off.


Raz_900
Member
posted July 05, 2004 10:45 PM
What type of fuel?

Timing set at?

Jetting/carb?

What spark plugs? If the heads were decked .020 " ( I hope it's not .200"!! ), the CR with flat tops will be around 10.5 or 11. Stock smogger plugs will blow pistons apart in hurry.

leftturn73
Member
posted July 06, 2004 08:37 AM
93 octane pump gas through a holley 4412 with 72 jets. Plugs look a bit rich. Timing is set a 36 degrees adv. Heads are 462 double hump heads 194/160 valves. Heads flat cut 20 thous flat top 2 brow pistions block decked. Plugs are autolite 353's. I have similar combination 355 flat top decked with 461 heads cut 10 thous. same plugs and I have run it for 3 years with no problems.
Any thoughts????????????


77k
Member
posted July 06, 2004 03:21 PM
What kind of pistons and what is the ring gap?


leftturn73
Member
posted July 07, 2004 05:24 AM
Speedway Hypermax top ring set at 20 bottom ring at 18. (SpeedPro Moly rings)
I do not think it is a ring cap issue because I see the on a couple pistons the tops starting to bubble and or small piece coming off. One piston is forming a small pin hole.
Heres a new twist. This is a 3 car team. I built a motor for only one car. Today I receive a call, the other two cars have just had the same problem. I have not touched the other two motors. Only thing common between the 3 is the pump gas and timing light.
After I put this one back together I will be setting the timing with my light, which I will have verified by my local Speed shop.


flatfoot27
Member
posted July 07, 2004 06:06 AM
Lot of compression for pump gas. I'd try a colder plug and back up to 32 on the timing.


mansfief
Member
posted July 07, 2004 08:39 AM
Get rid of pump gas. A friend ran pump gas (93) and he burnt his pistons. I was told that pump gas burns hotter and that is the reason the pistons burn. I spend that extra on 110 and keep an eye on timing.


Raz_900
Member
posted July 07, 2004 08:59 AM
A zero deck flat top with 461/2's is going to be around 10.5:1. That's VERY marginal on pump fuel and not feasible with 36 degrees.

I'd blend race fuel 50/50 with the pump 93. 50/50 with 110 will give you around 101-102 octane and with 115 would be around 104, which is enough for a 10.5 motor. Running straight 110 won't do anything but cost money and HP. Higher octane than what is needed will only cost HP.

I'd also switch to AR72 plugs. I think they're the coldest, gasketed plug Autolite makes. I used them in a set of 461s last year with very good results with 50/50 fuel (115 & 93)

Good luck!!

leftturn73
Member
posted July 07, 2004 12:44 PM
I just spoke with a local engine builder and he agrees that the pump gas is not enough. He feels because of the small cam, higher compression and 36 adv. timing the pump gas does not burn correctly. He also suggested running 50/50 fuel or run the lower end 108 fuel.
This was a learning exp.
Thanks for all your feedback.


leftturn73
Member
posted July 07, 2004 12:46 PM
quote:
Originally posted by leftturn73:
I just spoke with a local engine builder and he agrees that the pump gas is not enough. He feels because of the small cam, higher compression and 36 adv. timing the pump gas does not burn correctly. He also suggested running 50/50 fuel or run the lower end 108 fuel.
This was a learning exp.
Thanks for all your feedback.

Sorry I left out that he feels the chamber pressure is way to high for pump gas thus causing the bad burn.



77k
Member
posted July 08, 2004 01:59 AM
Go to a small airport and buy av gas.[100+octane] Reg gas around here is about $1.66. prem is about $183, airplane fuel is $2.00 a gal. You can add a little trans fluid if you want some top end lube.


mansfief
Member
posted July 08, 2004 11:57 AM
It is the pump gas. 93 burns hot and will do a job on the pistons. A friend lost some pistons with pump gas.


mini18r
Member
posted July 08, 2004 03:28 PM
quote:
Originally posted by mansfief:
It is the pump gas. 93 burns hot and will do a job on the pistons. A friend lost some pistons with pump gas.

I always thought high octane was a slow burn didnt realize it was colder burn also.So i guess if you want the best performance you need to push the envelope on the octane level,sorry if this sounds basic to you all, news to me.


Raz_900
Member
posted July 11, 2004 07:58 PM
The pump gas in and of itself doesn't run hot. It's the fact that it's detonating and preigniting that raises cylinder temps.

And yes, the higher the octane rating, the slower the burn. That's why getting just the right amount of octane required to avoid detonation makes the most power. Running higher octane fuel than what is really required just slows the burn down, which builds less cylinder pressure during combustion, making less overall power. A 9:1 motor on 94 octane will make more power and be easier to tune than the same motor on 115.

widebody
Member
posted July 13, 2004 07:07 AM
VP fuels makes a RED fuel, I think its 103 Octane. Ran my 10:1 motor perfectly on it, was a bunch cheaper than the 110 / 112 stuff.. check your plugs and jet accordingly ....just a thought


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