318 Magnum Dropped Valve

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J

JW MOPAR

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So very disappointed! Just about to finish my build on my 1965 Dart GT while fine tuning the engine #8 dropped a valve. The 302 heads have been completely rebuilt and I have maybe 15 minutes on the engine. What is the possibility that I also bent #8 rod, damaged the wrist pin or anything else? The valve broke right at the bottom of the keeper. I am thinking that the valve was week at that point and hopefully no other valves are the same. I am posting pics of the top of #8 cylinder and the bent valve. I am hoping to have the valve and valve keeper replaced, put it all back together and be good. What are your suggestions.

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wow, man that sucks.

the chances of damage beyond the top of piston are small, but they are also not zero.

however, the chances of you needing a valve guide are probably close to 100%

if it were me, i'd clean the top of the piston with burr and polish it nice so there's no hot spot, have the head checked out and replace what's necessary, knock it together and ship it with fingers (and toes) crossed.
 
I would be disappointed beyond words! Odds of a weak valve are slim. Check everything!!!!!! Guide, pushrod bent. Everything! Too expensive to risk.
 
There'd be no way I'd not get the other head off and inspect and or replace all of the valves. A trip to the machine shop at the very least to get checked out with a magnifying glass.
 
Rebuilt heads? I don't think so. Are all these valves new? Are you reusing the old valves? Bad idea.
 
As noted before, take the other head off for inspection. If you wanted to, you could measure the stroke on that cylinder and the opposite cylinder with a depth mic. Amazon product ASIN B08X7LRBHY Use a dial indicator to find TDC and then measure how far the piston is below deck. Istall a timing tape with zero line upo to the zero timing mark. Summit Racing SUM-167598 Summit Racing™ Timing Tape | Summit Racing
Rotate 90 degrees and subtract below deck dimension from BDC dimension. Rotate engine over at least three times and repeat each TDC and BDC measurent each time. Ideally, the dimensions will remain close (within a few thousanths) and consistent. That will give you some indication of the condition of that piston/rod/bearing in comparison to the other one. For the time and $$$, you'd still be better off pulling the pan and that rod and pison assembly to make sure everything moves like it should and checking the rod bearing while the heads are getting checked out.
 
pittsburghracer said:
New valve guides installed??? Just wondering if it was possible you had a tight one.
Click to expand...
that was my thought as well.

many moons ago i got lazy and snapped together a set of magnum RT heads without checking the guide clearance. wound up dropping #2 intake, but not immediately. on teardown inspection it was evident that it was too tight, naturally pulled both heads and sent 'em out. surprisingly that was the only one tight, all the rest were within spec.

lesson learned there.
 
pittsburghracer said:
New valve guides installed??? Just wondering if it was possible you had a tight one.
Click to expand...
Yep new valve guides were installed. Believe me I have gone through every scenerio I can think of trying to figure out what could have gone wrong. Machine shop that did the heads is closed for the holidays until 1-3. I'll post here what they have to say.
 
Could also be that the valve stem had too much run out and was not straight. My brother checks every single one and we order 25% more valves due to this as even a few thou can cause a problem.
 
Scody21 said:
Could also be that the valve stem had too much run out and was not straight. My brother checks every single one and we order 25% more valves due to this as even a few thou can cause a problem.
Click to expand...
Thanks Scoody21. I sure hope there isn't a potential problem with others in my heads.
 
I don't believe you've hurt the short block any more than the slight damage to the piston. They can take a pretty good beating before transferring damage to the bottom end.
 
Thanks RustyRatRod! I sure hope not. I am going with that assumption and putting it back together once I get the head repaired.
 
Sorry about the crude picture but what is going on with the piston in this area circled. Probably just the angle. Look at the piston right along the cylinder wall.

IMG_1097.jpeg
 
I was surprised that a machine shop asked me if I wanted them to check the valve guide clearances, that should be a given on any valve job. Also I've learned not to reuse the valve's as I had a valve break right below the guide boss, needless to say it not only broke the top of the piston but broke through the cylinder wall. The valve guide issue and the broken valve were both on the same engine a 302 ford
 
Studying your 318 build.

Your title says "Magnum 318", not looking like a magum engine.

It is looking like the 318 Roller Engine that came factory with the 302 Closed Chamber heads.

Also it looks like you have the replacement aftermarket 8.5 cr valve relief pistons, when the factory Roller Pistons were 9.2:1 cr flat tops. So this tells me someone has been into this engine before, possibly before your overhaul.

Used valves and valve seats have been cut recessing the valves down into the heads, and standing the valve stems up higher than stock at the valve spring tops.

So now into stock 318 roller cam or replacement higher lift roller cam, or a reground factory roller cam that equates to smaller camshaft base circles.

Leading up to valve train geometry, pushrod lengths and type of rocker shaft stamped rocker arms?

If rocker arm geometry is off it can push the tip of the valve stem back before it starts pushing it down.

All the little things off in the valve train can throw off the rocker arm to valve stem geometry, causing undue stress to parts.

Just some things to think about of why this may have happened.

Here are some comparison pics various parts.

Valves riding low in combination chamber, after reground valve job.
20240102_170954.jpg

Factory Flat Top Pistons
Screenshot_20240102-162632_Gallery.jpg

For comparison, new valves Standing Up higher in a 360 chamber.
Screenshot_20240102-170511_Gallery.jpg

318 aftermarket 8.5 cr pistons
Screenshot_20240102-164310_Firefox.jpg


☆☆☆☆☆
 
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