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) :crying2: P.S. Anyone ever remove spiral locks and know a trick for that?

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. ;)

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?

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. ;)

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...

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.

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 :)

I was also thinking about the larger gaskets...

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.

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?

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 :bonkers:

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.

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 :histeric:

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.

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.

You can't bore a 425 to 500. you're lucky to get it even 60 over. The 425 block is also lighter weight than the 472/500 blocks. They supposedly removed the weight from "unimportant places". As for all this talk about the 425 crank, I had a discussion with Al at MTS about that when I first took on this project and he was saying that those cranks are not as weak as some believe. He said his expierience was from racing them and most of the talk about the weakness of the crank was coming from bench racers. Me, being new to the world of Caddy motors, took his word for it. Hard to argue with a guy that has one of the few speed parts places for Caddy motors in the whole world. But, as for nitrous, I stayed away from it in a 425 also.

Sure the 425 crank won't just crack, but it can't be stressed too much. Seems to me nitrous would be a bad idea. Anyway even if I could bore out my 425, I need a running car to get around in. I may have found a good local 500, I need to check on that one..

You're preaching to the choir on the nitrous, that's why I didn't go that way on my 425. A small amount probably wouldn't hurt but I wouldn't use a 150 H.P. nitrous kit on it. I wonder if those cranks could be sent out to be nitrided. Or is it toughtrided. One of them is outlawed, but I forget which one. I'm sure Katshot knows.

Angela,
1st i have to say that i admire you ;) I don't know ANY women that "build engines" and "Teach Boxing" > My hat is off to you!

Have you tried the Spark plug with the 4 electrodes on it to see if you had enough clearance in your cylinder head? I saw one at Auto Zone the other day, it may have been made by Bosch, im not sure but it was a strange looking spark plug. The thicker head gaskets and different plugs would probably work > check out one of those spark plugs and let me know what you think. :spin:

Sorry I haven't let you guys know whats going on with this fiasco. I sent my pistons back to Ross to be re-machined to MY specs. I called Federal Mogul, the parent company of Champion and they gave me a plug which is slightly less protruding in the combustion chamber, but after the pistons are machined, the stock plugs will fit just fine...By the way, the person at Ross that talks turkey with you about piston dimensions and the general mechanics of a piston is also a woman. Her name is Jane... And being a onetime professional boxer I've met a lot of women boxers :D

Angela
I have followed mostly all of the posting on this and other boards but you seem to be more involved in the cad 425 than most, I to am intrested in the 425 cad for a number of reasons #1 being weight.So i've been waiting and watching for your posting of the progress of your project,I hope I'am not being to forward.believe I'am not trying too.

oyoung

Dude.... nearly 2 and a half years ago this was posted! I remember it :)....

Angela hasn't been around for a loooong time.... haven't heard anything about her since..... she is the only person that I know of that was doing a real high performance build on the 425, she also used to live like 20mins from me back in NY.... wonder where she is now...

BTW.... weight isn't a reason to pick a 425 over a 472/500... the weight difference is IIRC around 25lbs... nearly nothing. Throw the Edelbrock intake on a 500 and you are already under the weight of a stock 425.

Angela went with the 425 for the simple reason that it was free and she had it around. I was interested to hear the results on that engine also.

It seems like an awesome engine she had going. Way before my time though.

Night Wolf I guess I should notice the date on some of these posting,anyway the 1977cad S/M states that the 1977 425cu.engine is 100lbs lighter than the previous engine which was the 500cu.

Alright, so after an eddy, will 75 lbs lighter really be all that much of a difference?

I have a couple years of reading on me now... If there's a great reason you need ~100 pounds, and you are not shooting for a whole lot of power, a 425 might not be a bad choice. Plus you can pick them up for damn near free since most everyone goes for 500/472s. Anyway what're your goals with the vehicle and engine?

100lbs?

I remember it was just a lighter block and crankshaft... on CB7 I remember reading 25lbs or so.. I could be wrong.

Even if it was 100lbs... the 500 has more power out of the box, and go-fast parts will do more, that should negate the extra weight....

but if weight really is a concern, then the 425 is a fine engine... its a fine engine in either case, just outshined by the 472/500.