306 explosion!!!!! HELP!!!!!!!!

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ixlr8d

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Dec 10, 2010

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#1

• Dec 10, 2010

• #1

ok so i need help figuring out what blew my motor. im posting some pics of the heads first. My first question is does it look like the piston was hitting the intake valve. I had a new cam installed and had the heads off last year and I do not recall the line on all the intake valves. Any input will help. They are AFR 165cc on 306. Cam specs Im not sure but will post asap. http://gallery.me.com/shaned1979#100135

 

Dino Dino Bambino

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Dec 11, 2010

#2

• Dec 11, 2010

• #2

It certainly looks like the pistons were hitting the valves. It's only a question of whether it was happening because the PTV clearance was too small or whether the valve springs were too weak and you floated the valves at higher rpm.

 

Mustang5L5

That is…until I whipped out my Bissell

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Dec 11, 2010

#3

• Dec 11, 2010

• #3

Since not every cylinder is damaged, looks like PTV interference from valve float. What heads and springs are those?

 

2000xp8

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Aug 8, 2003

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Dec 11, 2010

#4

• Dec 11, 2010

• #4

It's hard to tell from the pics, what's the condition of the crank?
Valve float usually causes valves to get bent up and the car to run like crap.
For it to break a piston, the head of the valve would have probably had to come off and bounce around in there.

 

LarsD

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#5

• Dec 11, 2010

• #5

I assume the block is shot because of the rod in the oil pan? What were you doing when it went? Were you on it shifting hard or cruising around?

 

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ixlr8d

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#6

• Dec 11, 2010

• #6

The motor is 5 yrs old prolly 50 passes and I wast exactly easy on it those 5 years. I had a comp custom ground cam put in earlier this year and the guy who did it made sure ( so he says) that everything looked great or he would not have put that cam in. He also replaced to stock Afr valve springs with heavier ones to avoid valve float. I did have a rocker stud break once which luckily only mushroomed the top of the valve. So I put all new studs in pushrods an the bent valve. The guy that put the cam in informed me that the only way I was going to get big hp numbers and low ets was to spin the motor up to 7500. Which I do beleive is alot for a stock short block. I used to run up to 7k but never above. The car was very consistant 12.4/12.6. When it blew I was coasting in neutral at 40 mph snapped the throttle to 6k and that was all she wrote! It does look like the cranked walked as the flex plate has marks where it hit the block. But what I was doing at the time of the explosion doesn't seem to me the outcome should have been so severe. The intake valve broke on #1 then I guess all hell broke lose. I have holes in my pan wholes in my block holes in my piston holes in my head metal in the intake and three broken rods. # 5 broke off the piston and the crank. Thanks guys for all your input. I may have ran her hard but I respected her and spent alot of time doing what I could do to make her last a long time. It just a shame.

 

LarsD

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#7

• Dec 11, 2010

• #7

7K? Holy $^%*

 

Mustang5L5

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#8

• Dec 11, 2010

• #8

He told you to spin to 7500 rpm on a stock bottom end? Holy crap!

 

giddyup306

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Oct 22, 2002

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Dec 11, 2010

#9

• Dec 11, 2010

• #9

Looks like the stock rod bolt let loose.

 

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ixlr8d

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Dec 12, 2010

#10

• Dec 12, 2010

• #10

I made a mistake it was an exhaust valve and I was told all the valves hit the piston after the timing chain let lose. I was also told the heads should be fixable. I have a 84/85 302 non roller with only 15,000 miles on it. I was going to use that. Should I convert to a roller or leave it?

 

giddyup306

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Oct 22, 2002

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#11

• Dec 12, 2010

• #11

ixlr8d said:

I made a mistake it was an exhaust valve and I was told all the valves hit the piston after the timing chain let lose. I was also told the heads should be fixable. I have a 84/85 302 non roller with only 15,000 miles on it. I was going to use that. Should I convert to a roller or leave it?

Click to expand...

I don't see why the heads wouldn't be able to be repaired. I had a worse case about 8 years ago with my Edelbrock heads. The pics are hard to see, but I didn't see any damage, just debris.

If it were me I'd convert it to roller, but if you want to turn more than 6,500 get a nice set like Jesel or Crower.

 

2000xp8

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Dec 14, 2010

#12

• Dec 14, 2010

• #12

Couple things i'd like to note, to get max power for track use, guys do run engines up that high. Most aren't into getting every last tenth of a second out of a 306 so it doesn't happen often, and it's not a setup meant for everyone.

Snapping the throttle without a load is the equivalent to missing a shift and while missing a shift in the average guys car isn't too bad, in a situation such as this, it could turn ugly.

Would appear to me that a rod broke, engine went unbalanced and that was the end of it.

Sucks to blow up an engine, i know i blew up a few. But sounds like you got decent time from her, and honestly none of them last forever.

 

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ixlr8d

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Dec 15, 2010

#13

• Dec 15, 2010

• #13

I knew something was up when I took it out in the morning and ran it up to 7k it just didn't seem to have any ass up high. I know guys shifting at 6500 and pulling better 60 fts and better ets. Something wasn't fight from the beginning. Two different cams and still hardly any change in my times. Might just throw a bb in her and be done. Thanks for all the input. I do have one question if revving it is so hard on it why do guys at the track rev up in neutral before they stage? I've never seen a car blow up in neutral doing that?

 

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ixlr8d

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Dec 29, 2010

#14

• Dec 29, 2010

• #14

Took the engine apart last night and took the pieces to a professional. The verdict, not enough valve clearance. So a lesson learned that just because people can talk a good talk and have a flashy website does not mean they know what the hell they are doing. Also learned that roller cams do not make power above 7200. The lifters bleed off. If you want to rev higher than 7 you need flat tappet. So the cam that had a power band from 5800-7500 and was supposed to make miracles happen only did the opposite. I also learned that if your going to take your stuff somewhere make sure that the person doing it does engine work full-time not just as a hobby.