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Author Topic:   Here's one that's got me confused....
KPLugnut
Dirt Forum Champ
Total posts: 1019
posted June 09, 2005 02:04 PM  
I have a customer who can run a 25 lap feature with their motor and the temps in the motor stay just fine and within reason and it runs FAST....but if they run a 30 lap feature, every single time on lap 27 or so, it will get VERY hot, nearly peg the water temp guage, and swell the radiator as tho there's a broken head or gasket failure causing cyl pressure to swell the radiator.

Has anyone ever seen this symptom? I haven't seen it be so predictable and what's even MORE weird is that the motor runds GREAT for 25 laps or so (and has done that 2-3 times now)....

Suggestions, ideas, help greatly appreciated.

KP

dode
Dirt Forum Champ
Total posts: 613
posted June 09, 2005 02:15 PM  
That thought had crossed my mind, but the motor doesn't lose power as though it was leaning out (or even miss a beat at all), it just suddenly goes WAY hot and pegs the water temp guage and then blowz up the radiator like a balloon....

thanks for any help at all here, guys...

KP

ctfarm
Dirt Freak

Total posts: 206
posted June 09, 2005 06:29 PM  
I had this happen to me in the late 70's,chased the problem for three weeks,the motor was leaning out.Fattened up the jets and bumped up the fuel pressure.You did'nt say how hot was ,it may be close to overheating.If it sees lean at race speed,it only takes a few seconds to get hot.Had another motor do this,years later, and found out too late that the spark plugs were too hot.


racer038
Dirt Maniac

Total posts: 111
posted June 09, 2005 09:03 PM  
I had a similar problem. Started usually right at the end of 10 laps. The radiator would puke but the temp was only 210. By 20 laps the radiator had puked most of the water, and the engine would get HOT HOT. Compression and leak down never showed it. I pressurized the radiator daily for 4 days, then pulled the plugs and watched as the motor cranked. I got a mist out of #1 and #8. Pulled heads, both gaskets failed in exactly the same spot, allowing compression into the water jacket. Heads checked out good. New gaskets (not felpro 1004) and it's been sweet ever since. Hope this helps.

sdhnc29
Dirt Forum Champ
Total posts: 934
posted June 09, 2005 09:35 PM  
What type of engine KP ?
Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780
www.hendrensracingengines.com
www.experienceodessa.com

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted June 10, 2005 06:56 AM  
Steve,
It's in an SST mod here in the northeast. They are steel head, flat top, 2bbl motors with 2101 spec intakes, and they are in Troyer style pavement mod chassis with 10" rubber.
I'm not exactly sure of every detail but what I was told by the driver is exactly how I worded my original question. Kinda hard getting real details, but I'll try again to day for more info.

Thanks in advance for any help,

KP

rfb320
Dirt Maniac

Total posts: 150
posted June 10, 2005 10:21 AM  
A friend of mine could always rint he heat just fine and then on about lap ten of the feature the car would get hot and he would have to pull off. He chased the problem for weeks. It turns out that he had overheated the car 1 time swelling up the radiator and when that happened it closed all the fins on the radiator so it couldn't pull air thru. He took it out and you couldn't even see through it. Put in a new one and problem solved. Just something to check.

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted June 10, 2005 11:43 AM  
thanks, guys, for the info. they're on their 3rd radiator now, and although I haven't heard from them today, I'm leaning towards the cracked head or head gasket failure theory.
I'll let ya know when I hear more.

Thanks,
KP

sdhnc29
Dirt Forum Champ
Total posts: 934
posted June 10, 2005 04:06 PM  
Yes the only way the radiator could bulge would be from combustion pressure. Unless of course they are doing something stupid like adding a second rubber seal to a 25lbs radiator cap. This would raise the pressure in the radiator, and cause it to bulge over time. I've seen this happen before.

If they are not doing something like that, then is just about has to be a cracked head or cylinder wall. You would think that a head gasket would add radiator pressure at any temp.
Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780
www.hendrensracingengines.com
www.experienceodessa.com

eborcim
Dirt Freak

Total posts: 303
posted June 10, 2005 10:39 PM  
Steve, what pressure cap do you recommend?

o5racer
Dirt Freak

Total posts: 402
posted June 11, 2005 12:21 PM  
How much water is still in the radiator after the feature?
Nick

JohnG
Dirt Maniac

Total posts: 137
posted June 17, 2005 09:19 PM  
my motor would do that around lap 15 on a half mile track, but it was fine for 30 lappers on a quarter mile track!!!! same rpm at both.

the pistons were kissing the head and lifting allowing compression into the water.

the pistons were kissing the head because the main line was bad, after replacing 2 broken pistons the crank finally broke and i figured it all out.....

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