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Discussion Starter #1
I just purchased (But haven't picked up the motor yet) a 1974, 350 SBC, 2 bolt main motor. It is a 3970010 block ID# VO511CKW. According to the seller, who was given the motor by a friend, it also has a 400 crank and rods for a 383. Per the seller, the motor was rebuilt about 5 years ago and bored 30 over with all new parts installed.

The seller pulled the heads and found that a valve had broke and a back piston had hit it. He said the piston is fine, but dinged.

Questions:

1) The heads will need to be reworked and at least one valve replaced. Do you think the dinged piston will be a problem. What type of collateral damage should I look for?

2) What do I have as far as a buildable street engine, if it has a 400 crank with 383 rods? Do you think this 400 crank with 383 rods caused the valve problem (valve to top of piston clearance)? The pistons appear to be standard w/4 half moon areas on each one (Based on photo' I have seen of block w/ head removed)

I would appreciate all inputs! Once I have an idea, as to what I have on hand, then I'll be able to ask advice on building it for my 1969 Z28, as a street engine.

Thanks;
John Lighthart
Charleston, SC
 

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The DING in the piston is no big deal as long as its not on the edge of the piston. Any high spots can be filed off flush. I have had this same thing happen but it was six valves and nine pushrods all in one shift. (6400rpm). The reason behind it was that the gear drive I was running sheared the key and everything slammed together. What was the engine used for? I am pretty sure that the 400 crank and rods had nothing to do with this. When using a 400 crank it has to be machined into the block it can't just be bolted in. What cam was in the motor at the time of damage? Most flat top pistons have 4 reliefs cut into them These are the valve reliefs so the valves don't hit te heads at higher rpms. Does all of the other pistons look OK? My guess is that a retainer came off the valve OR a valve spring has broke this will cause the valve not to retracked after the rocker has depressed it. This would cause the valve to fall down onto the piston and get destroyed. I would get more info befor ethe purchase.
 

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The seller did say that it appeared that a retainer failed causing the valve not to close properly. I already purchased the motor and will be picking up the motor from North Carolina this weekend. I will collect more details and get back to you. Thank you for answering my inquiry; At 50 plus viewings, I didn't think I was going to get any input.
John Lighthart
Charleston, SC
03/19/07

The DING in the piston is no big deal as long as its not on the edge of the piston. Any high spots can be filed off flush. I have had this same thing happen but it was six valves and nine pushrods all in one shift. (6400rpm). The reason behind it was that the gear drive I was running sheared the key and everything slammed together. What was the engine used for? I am pretty sure that the 400 crank and rods had nothing to do with this. When using a 400 crank it has to be machined into the block it can't just be bolted in. What cam was in the motor at the time of damage? Most flat top pistons have 4 reliefs cut into them These are the valve reliefs so the valves don't hit te heads at higher rpms. Does all of the other pistons look OK? My guess is that a retainer came off the valve OR a valve spring has broke this will cause the valve not to retracked after the rocker has depressed it. This would cause the valve to fall down onto the piston and get destroyed. I would get more info befor ethe purchase.
 

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if the valve hit the piston got to turn the cylinder to top dead center and measure from top to piston. than turn another cylinder up and take reading to make sure rod isnt bent. all it takes is 1 hit and rod bends be careful
 
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