What would you do?
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500, 472, 425, 368 Discussion, What would you do? in Cadillac Engine Technical Discussion; As some of you know, I'm building a Hi-Po 425. I had Ross make me a set of pistons that ...
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    Angela Desmond is offline Cadillac Owners Fanatic
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    Question What would you do?

    As some of you know, I'm building a Hi-Po 425. I had Ross make me a set of pistons that would make 11:1 compression. They have a huge dome because my chambers measured in at about 114 cc's after unshrouding the valves a bit.It seems that Ross made a nice piston except that they didn't leave enough room for a stock spark plug to screw all the way into the chamber.It's not the dome that's the problem. (The dome is on the other side of the chamber).When I cut off the electrodes, the plug fits O.K. , although I haven't made a clay mold to check vavle and plug clearence yet, but at least it screws all the way in at TDC. Ross has offered to take back the pistons and re-machine them, or they said I could machine them myself with a diegrinder. I really don't like the idea of doing this myself, as one wrong move and the piston becomes a paper weight. For them to do it I have to get the rods off and they have "Spiral Locks" holding them on and I've heard they are a nightmare to get off. I found them easy enough to get on though. I think another option would be a racing plug that doesn't have the protruding electrodes.So, anyone ever expierience a problem like this?Even if not, any good ideas out there? This is one that has me kinda stumped( and upset) P.S. Anyone ever remove spiral locks and know a trick for that?

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    Katshot is offline Cadillac Owners Master
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    Re: What would you do?

    Damn, that sucks! Dumb question, are you using the right plugs? Is a shorter reach plug possible? If it's down to using surface gap plugs or taking all that crap back apart, I'd go with the surface gap plugs. They're more resistant to fouling anyway.

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    Angela Desmond is offline Cadillac Owners Fanatic
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    Thanks for the quick answer, Katshot. I trust your opinion. I used the original AC plugs that ran the425 when it was in the 79 Sedan DeVille. Those spiral locks are tough to get off, huh? I'll call the speed shop and see if I can get a racing plug to test the clearence.Would it be stupid to try to use a couple of gaskets instead of one on the stock plug? Or go with the larger gaskets I see in the indexing kits?

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    Re: What would you do?

    The spiral locks CAN be a PITA for sure. Generally, I don't have too much trouble though. I thought about doubling up on the gaskets, and it might work. I guess I'm just leary about giving you only the amount the extra gasket would net you. I'd rather get the plug WAY out of the way.
    The larger gaskets from an indexing set would be a neat fix too I suppose (didn't think of them). See, I told you you're pretty slick.

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    Angela Desmond is offline Cadillac Owners Fanatic
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    I'm slick with book theory. It's another story having to put these things into practice. I think I'm in some unchartered territory with this 425. Most people build up the 500 and 472. I never realized how big the dome was going to be on that piston to achieve 11:1. Up 'till now my expierience has been limited to mild build-ups of Chevy small blocks where there is tons of info around and also parts for the job. This winter I'm going to put together an engine stand that I can run this motor on before swapping it in and finding all sorts of little problems here and there. I know there will be plenty...

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    Re: What would you do?

    Good idea but do you have a plan for loading the engine? In other words, you need to apply some sort of drag to the engine like an engine dyno does. Just letting it sit there and free-wheel is risky for the engine. Parts "float" when not under a load.

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    Angela Desmond is offline Cadillac Owners Fanatic
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    I hadn't thought of that. Would even at idle be a problem? I wanted to at least break in the cam on the stand and that's a pretty fast idle! I'm not sure how to build something that would imitate a load on the engine. I better put my thinking cap on.I'm so busy right now. Just finished putting that Ford 9 inch in the Caprice. Got a vibration now that we all suspect is the old driveshaft so I'm having a Heavy duty one made. It took a while to find the right u-joint for this set-up 'cause Curries forgot which pinion yoke they put on there.First they forgot to put the upper control arm brackets on it and it had to go all the way back to the west coast for them to fix that.Also just got done putting a head gasket on the old M-37 Dodge. Intake gaskets to, and I still have a vacuum leak that's driving us crazy. We suspect the metering valve( the old type of PCV valve). Now this crap with my new pistons. It never ends!...I should have taken up knitting

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    MMNineInchNails is offline Cadillac Owners Enthusiast
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    I was also thinking about the larger gaskets...

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    Re: What would you do?

    That's the reason I don't do custom cars much anymore. Too much headache.
    Personally, I wouldn't run the motor at all without a load on it. You could float a bearing in a heartbeat and that quick all your work and money are turned to junk.

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    Just wondering, why are you building a 425 rather than a 472/500? I'm sure you know they're the same dimentions. Plus, the 425 has a weaker crankshaft. Wassup with that?

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    Angela Desmond is offline Cadillac Owners Fanatic
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    Had the 425 just laying around; which means for free. Besides, I'm always the wack that has to be different. I'm not to worried about the crank 'cause I'm not going to spin it more than 5500, tops..I wasn't aware of bearing problems without a load on the motor.By the time I finally get this project finished, I can use the motor to power a generator for the next blackout

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    Hi Angela,

    Keep us posted on your 425 as I am very interested in what your doing. I too picked up a cheap 425 to build. Just finishing tearing it down and making decisions on what to do. I got a catalog from MTS and have talked with Al on an occasion or two. Maybe he can offer some assistance in your quest for a HP 425. I hope to have some serious fun with mine, but am still looking for a 472 or 500 for later.

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    Angela Desmond is offline Cadillac Owners Fanatic
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    Yes, MTS is where I purchased all my aftermarket equipment. Al and I talk frequently, unfortunately it's about problems like my pistons or not getting enough lifter preload with the pushrods that were sent to me. If your going to spin that 425 over 4500 I recommened using the shaft rocker system. There is an inexpensive one that is not roller but works much better than the stock set-up.I too would like to do a 500 in the future, with nitrous or a blower this time.All I need is tons of cash

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    Yesterday I bought a 78 Fleetwood Brougham with a 425, so this is of interest, but I think I'll get a 500/472 and build it while keeping the 425 to drive around with, then put in the 500/472 when it's ready. Nitrous on a 500 would be fun, but nitrous on a 425 would suck when the crank broke. Anyway good luck with your 425.

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    the 368, 425, 472, and 500 are all in the same engine family. Just bore you're 425 to a 500 and change the crank and get new heads and such.

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