This started about five years ago as a 496 build. I began acquiring parts here and there as various deals presented themselves. TKO 600 - $1500. 454 - $200. Eddy Perf RPM heads - $1500, etc. And then it happened. I work across N. America and while in Michigan, came across a Mercruiser 502 last fall that the guy dropped a supercharger on and proceeded to nuke the engine. #1 and #2 rods broke about 1" above the crankpin and took a few small chunks out of the bottom of #1 & #2 bores. Here's a shot of the damage:



I picked this mess up for five bens and after a couple more, got it shipped back home. I was able to sell the heads for $400, the crank for $200, the rods for $250 (I happened to have two others to match them). Which left me with a 502 block and about $150 in the black. Because of some scarring in the bores, I ended up sleeving both 1 & 2 since the recommended overbore on these Gen VI blocks is only +0.030" and they wouldn't clean up at that. The block was then checked for any other problems and then machined Here's a shot of the one of the sleeves installed before I had it decked:



Anyway, I originally meant to build the 502 instead of the 496; for a few days anyway. The allure of building a bigger big block, however, was already working away and after Snowman's build via Jim (427Hotrod) last fall. I ended up selling most of the 496 parts I had accumulated.

I Picked up a Gen 6 Eagle 10 under 4.25" 4340 crank for $500. I kept the 6.385" bushed scat rods and added a set of SRP pistons & rings:



Here's a shot of the crank in the block:



To be continued. . .

 

This is gonna be fun!! I know where we're heading!!

JIM

 

That's awesome! Always great to see a smart build from good buys.

Any concerns about the damage on the bottom of the bore? Did you consider adding just an inch or so of block filler?

 

Nice project, please keep us updated

 

So...you can get 540" out of a stock but bored 502 block with a 4.25" crank? I didn't realize the bore on a 502 was THAT much bigger....

I always see 540s built out of Dart, Merlin blocks...I didn't know you could get that out of a 502....

I just happen to know where there is a good running 502 available....hmmmm

 

The sleeves were installed full length and then contoured to match the bottom of the bores so there shouldn't be any issues. The damage from the rods didn't compromize the water jackets at all. I haven't really considered adding any filler, but it's still on the stand with the freeze plugs out. You think it's worthwile?

Yup, factory 502 blocks are supposed to be good for 700 hp. I've read about several that were in the 800 hp range.

4.47" bore + 4" stroke = 502
4.50" bore + 4.25" stroke = 540

GM says the block will take a 4.6" stroke. With the standard 9.8" deck height you'll start getting excessive rod angularities IMHO. Plus, pistons are a custom order for a reasonable street comp ratio.

 

Thanks guys! More pics coming.

 

Nice, but one thing to be aware of. The aftermarket blocks like Dart and others, have lifter valley bosses that accept head studs that replace what would otherwise be missing head bolts on 4 of the cylinders. You don't have that option with your block, so you might want to keep the compression ratio as well as the final HP number on the modest side. That way you won't have too much risk of blowing the head gasket in those areas. Some builders call those missing head bolt areas, blow holes. But keeping that in mind, you should be able to stay out of trouble and have a real nice motor. Enjoy

 

Hanging out with Jim (427 Hotrod) can probably be fun, but also likely expensive. He is a wealth of knowledge and good for morale.

Keep up the post, sounds like it will be a interesting build to follow.

R.J.

 

Kinda makes you think that if you (or I for that matter) had originally built a 540 cu in you (I) would now be 'hankering' for a 632 or 706 cu in

 

Sleeves shouldn't be an issue, there's very little force applied to the lower part of the bore since there is very little angle between the rod pin and wrist pin. I have a Big M getting a pair of sleeves for the same reason and plan to whoop on it like I stole it including some pretty hefty doses of spray.

 

With proper installation of the sleeves, which I'm sure is the case, I don't think so. I guess I was just brainstorming a bit that if there was any general weakening of the area a little Hard Blok wouldn't be a bad thing.

You've got a good shop - I'd be interested in hearing their thoughts

 

I mentioned in the original post I picked up some Eddy RPM's. Since their flow numbers are somewhat weak, particularly for this size of engine; I flipped them on ebay along with a number of my other 496 parts I wouldn't use. I planned on getting a pair of AFR 325's with the CNC chamber option; but came across these instead for $1450/pair last winter. Edelbrock discontinued them and dumped their remaining inventory in their E-store. They are a 325 cc CNC head (well, mostly) with 112 cc combustion chambers. This yields a 10.8:1 static comp ratio, but the cam is 254* duration so it'll still run on premium.



These are a CNC ported version of the Perf RPM heads, and while they don't quite keep up with the AFR heads after 0.400" lift, they do have some really impressive low lift flow #'s. The exhaust port is particularly improved over the RPM head, and it's still in the stock location. Here's how they stack up to the AFR's:



The AFR #'s were from a CC (?) article and Edelbrock's are from their website. Here's some shots of the CNC work:









The combustion chambers and exhausts are fully CNC'd, but the intakes are only bowl blended and port matched. Edelbrock didn't exactly mention that! Quite frankly, I was disappointed in the CNC work on the intake side. there were fairly substantial ridges left where the CNC work met the original casting of the runners. A few hours of work with the die grinder fixed 'em up nicely though. You can see this in the intake port shots.

The springs are pacaloy with 145 # on the seat and 465 # at 0.670 lift on my cam. The retainers are 10* Del West titanium to help lighten the valvetrain up a bit.

 

I asked and they didn't have any concerns other than to say don't go more than 0.070" over with them.

 

The newer 502's can go 4.600, but I don't know when the break happened, they're very similar to the Gen 5 Sportsman blocks except for splayed mains and coolant holes in the deck. Sonic checking is the only way to know for sure, but you're fine at 4.500 with any 502 block.

 

Well, I just found out my SD card is junk so this pic will have to do:



I don't have the oil pan on yet, due to a fitment issue, so here's the bottom end:



Main bearings are at 0.030", except #5 which is 0.035". Crank thrust was 0.003, but with a sheet of 600 grit wet/dry and a piece of glass, the thrust is now 0.007"

The rod bearings are 0.020", which is slightly less than what I was shooting for. This is with the one thou oversized bearings too. I didn't really want to grind the crank so this is where they're staying.

Top ring gaps are 0.022",
Second rings are 0.025"

Deck height ended up getting blown a bit. The RH bank is 0.002 in the hole, but the LH bank is 0.008". I was shooting for 0.008" for a total quench of 0.0045 with the gaskets I'm using. I'm not sure if I blew the measurements or the machine shop missed the mark here. I used a machinists straight edge, a dial indicator to bring the pistons to TDC, and a feeler gauge. The LH side was 0.020" in the hole and the RH side was originally 0.028". The LH bank has 0.041" quench and the RH bank has 0.047" it's a little tough to add it back so the heads are now on.

Since the Gen 6 blocks use a different oil pan than the Mk 4 blocks, you are somewhat limited. I went with a Moroso 20411 pan. It has the trapdoor setup like the original corvette big block pan, is kicked out for additional capacity, and is 8" deep. Here's some stock pics of the pan:





One problem, the pan interferes with the front main cap. I sent it into Moroso and they test fitted it on one of their engines with, of course, no problem. Fitment over the rear pan seal is a bit questionable too. there's about 3/16" more of the seal exposed than at the bottom. You can see the flange isn't quite square to the oil pan rails. But of course, "that's how it's designed" I'll retake the pictures once it shows up again from Moroso.

 

30 thousands on the mains I hope that not your bearing clearance and the rods are 20 thousands on the rods.

Or is that a crank thats been turned .020/.030

 

Whoops - not enough zeros there :o. Good catch. 30 thou could be a problem.

The crank is ground 10 under on the mains and std on the rods.

The main bearing clearances are three thousandths (0.003") the rods are two thousandths (0.002").

 

That sounds much better and those clearances look fine for your build.

 

OK - got the valvetrain installed and set up today. Encountered a few minor issues since I'm using 1.8 ratio Harland Sharp rockers. Before I put the heads on, I did a mock-up. Since the higher ratio moves the fulcrum point inwards, I had to grind a 1/16" radius into all the guideplates for clearance. In addition, I had to clearance one of the exhaust pushrod slots on each head. Edelbrock apparently leaves a small lip on what would be #3 or #6 exhaust. This wouldn't be an issue with the standard 1.7 rockers, but mine just touch the castings. A little tlc with the die grinder and





Another 'issue' is the intake rocker on #1 and #8 interferes with the indent for the valve cover bolt. Luckily, I'm using stamped steel ones or the rockers on the intake side may have really needed some surgery. In my case, a little shave off of the edge of the rocker was all that was needed.



It almost seems a shame to have to put the valve covers on!



Oh, cam specs for those interested:

Hydraulic Roller Cam
Intake: 254* @ 0.050", 0.666" net lift
Exh: 260* @ 0.050", 0.670" lift
Lobe separation: 114*
Intake CL 112*

Pushrods are "Doug Herbert" aka Manley (they even come in Manley boxes) 0.080" wall pushrods, 7.70" intake and 8.70" on the exhaust side.