FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: janjon on February 23, 2015, 07:11:16 PM
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I bought my car with a 350 SBC roller motor not knowing many of its particulars other than aluminum rods. It started smoking a bit from #8 zoomie stack and oiling the plug a bit. The car also needed a new flexplate so out came the roller motor and in went a milder 350. Upon removing the intake I find that the intake port wall (340292 head) has a hole where some extremely industrious but hopefully talented individual ground just a little tiny bit too close to the pushrod clearance hole and the intake port was sucking oil from the valley. 'Splains why cranking pressure and leakdown % not real bad. A whole lot of handwork went into these heads, both ports and chambers, in fact, one might say a little TOO much.
The head is removed and I am shocked to see... FLATTOPS!!! I expected to see domes of some sort.
So a repair was attempted, (a freebie) but the repair has a similar hole. It has been suggested to me that epoxy in the runner would work to seal the leak. It would have to be in the runner because pushrod clearance to the outside is just about zero. I don't care what restriction that might cause, but am a bit concerned what might happen downstream if it came loose. Anyone have any thoughts on this?
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Cast iron head repair is tough.
My suggestion is to use epoxy on both sides and re-clearance the pushrod side.
By putting it on both sides it can flow thru the hole to the pushrod side and have a larger area to grab on to.
Leave some extra in the intake port side for strength.
Start with cleaning the head really good. Take a prick punch and roughen up the surfaces so the epoxy
has something to grab a hold of.
Do a little less port work and hope it works.
The nice part about a FED is you can watch those pipes and see a problem! 8)
Matt
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I had to switch out a couple of roller lifters to ones that had offsets in the push-rod cup in order to get clearence
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Yes Bruce is right, on my IRON SBC, I have .150"offset push-rod centers in my intake lifters to have more clearance and straighten the push-rods and .050" on the exhausts. I have seen a race team put so much epoxy on the push-rod side that it looked like the push-rod was going thru the intake port, all to make the intake ports even wider. They even had a cam made to move the lobe over to help straighten the push-rod. Also you made need to get offset shaft rockers to get everything to line-up.
As the saying goes "speed cost money how fast do you want to go ? "
As far as the epoxy to fix the overly ported heads, I would think just on the push-rod side would work, but check with any good head porter, they'll know. Some head porters use epoxy to change the shape of the ports to increase port air speed.
Jon
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Janjon Don't be afraid to use epoxy on the intake port. Every one of my intake ports has epoxy in the pushrod area . The best epoxy to use is called Splash Zone and you can get it from a marine supply store . It is water solable and very easy to work with . When I get a chance I will post some pictures of my heads .
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Thanks to all for the input! Now I feel gooder about trying to fill the hole.
John
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Now to the flat-top side of the equation... the intakes measure about 2.070 at there largest diameter, you could get about a .015" feeler gauge between the intake and the exhaust valves on any given cylinder, and the edges of the intake valves hang about 1/64'' or so below the deck of the head. This would seem to indicate that the heads were decked severely to gain compression ratio with the flat-tops. Any thoughts here?
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"Clay" the piston to valve clearence
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We learned another tip on measuring p-v clearance, from a well know race motor builder, insert a 5-6" of solder into the spark plug hole, hand rotate engine, pull out solder and mike it, a simple clean way to get the clearance. Just insert it twice, one toward the intake valve, 2'nd toward the exhaust.
Again, the more compression the better when burning alky.
Have Fun !
Jon
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jon
a smart man once said shut the pie hole and open the two holes on your side of your ace ::)
your solder tip into the spark plug hole will be use this weekend :D may have just save some money to go racing on 8)
as always
thank you for your time
steve m.
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To be clear, the motor has punched the car down the track a bunch of times before I removed it from the car, so I'm not worried about p-v clearance at all, just sort of perplexed that someone would take the flat-top and-whack-the-xxxx-out-of-the-head-deck approach to build compression. Possible theories about combustion propagation impeded by large domes? Possibly the engine builder giving the customer the desired compression ratio with the parts supplied? Not that I know what the compression ratio is either. Not that I don't know how to determine it either. But I'm too lazy to do that.
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JanJon, your heads may not have "been-whacked-to xxxx" to get compression. My JF SBC heads have not been milled, and my intake valve stick out from the edge of the deck surface of the heads.
When I have time, I'm getting our dragster ready for the March Meet, I'll take some pictures of my current heads and post them here.
In the meantime, here is a picture of one on my busted heads, when the trans shifted into neutral instead of high gear and the motor went to 12,500 rpm. Just look at the good combustion camber , not the busted one. If someone milled the xxxx off you heads you would have alignment issues, with head bolts, intake manifold etc. Bottom line no matter how much energy you have, a good race motor has higher compression than your "back-n-forth " work car. And even higher compression if you are burning alky. You'll be surprised how much higher compression will "wake up your motor !" 10 Custom made [ with mold] Pistons , rings, pins cost me $1200, I think off- the- shelf high compression pistons will be allot less. Our current pistons are from CP.
I hope this helps,
Jon
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JanJon, your heads may not have "been-whacked-to xxxx" to get compression. My JF SBC heads have not been milled, and my intake valve stick out from the edge of the deck surface of the heads.
When I have time, I'm getting our dragster ready for the March Meet, I'll take some pictures of my current heads and post them here.
In the meantime, here is a picture of one on my busted heads, when the trans shifted into neutral instead of high gear and the motor went to 12,500 rpm. Just look at the good combustion camber , not the busted one. If someone milled the xxxx off you heads you would have alignment issues, with head bolts, intake manifold etc. Bottom line no matter how much energy you have, a good race motor has higher compression than your "back-n-forth " work car. And even higher compression if you are burning alky. You'll be surprised how much higher compression will "wake up your motor !" 10 Custom made [ with mold] Pistons , rings, pins cost me $1200, I think off- the- shelf high compression pistons will be allot less. Our current pistons are from CP.
I hope this helps,
Jon
OUCH!!!!
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X2^
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That's right, it's not fixable, but my head guy can weld-up and fix damaged iron heads, but not that bad !
Bob McKray Performance, the engine builder & tuner on the JrFuel car Don Enriquez has driven for the last 20 ? years, including the last 3 years of NHRA Heritage JrFuel Championships, 949-458-7087 [ SoCal]. If you send him your SBC iron heads he can port them just like his for $1500 pr.
Included is our 2014 March Meet winner's circle picture, BTW we won the 2013 MM too.
Jon
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On the east coast our dirt modifieds have a flat top piston rule so we fly cut the heads and get them down to 47cc combustion chambers and 13 to 1 compression 245lbs maybe the engine was built for a different purpose I have two of thease engines left over and im using them in a digger.
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Thanks to you all for the responses and advice. I shall proceed accordingly.
John
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Jon, how did y'all do at the march meet?