The elusive 224/3.7 MerCruiser banger

A fully counterweighted crank would help out a lot. These cranks don't have a uniform counterweight structure to have equally opposing mass 180 degrees apart. In an inline, that really benefits the crank and harmonic shake....

 

Welcome @Charles Easter,

There are a bunch of builds on here with many variations. The more you read the more you will develop your own ideas. This is one of the things that I really like about this thread. So many guys wanting to try different things, just like the earlier days of hot rodding.
I have three engines. The one I am working on first is almost stock with the exception of an aluminum head, dual carbs and headers.
The next one will be bored and stroked.

If I get to the 3rd, it will be REALLY WILD! At least by my standards

 

I thought they were for replacing these on internal balanced 429-460's

I have the weighted kind in a drawer somewhere. It was wrong for whatever we were building. Mike

 

The FE's used a straight wall extension like was posted earlier as well. Most performance 460 builds eliminate those counterweighted sleeves, they are really outdated, and just use a conventional counterweighted harmonic balancer with the seal snout made onto it.

 

I vote go for the wild one first!

 

I am on a wild trip, too...

 

Doug,
There are several things to work out with versions 1 & 2 before spending the MONEY on the Big Gun!
Besides, I have to keep some in reserve in case the guy with my favorite '32 roadster decides to sell.

 

Well, you know me, if a little is good, too much is just right!

 

Which is exactly why I like your roadster

 

Anyone know the bore spec and tolerance for the big end of the connecting rods?

 

I have that info but am not at my shop right now. Will post later.

 

I've seen several Bonneville build threads where guys have welded counterweights onto cranks to make them fully counterweighted and worked out fine.

 

Here is the engine part of the service manual.

 

Thanks. My manual didn't have the number.

Looks like my rods are solidly within spec. I think I'm gonna order up a set of OEM bearings and cross my fingers that the ones I got were thou under or something.

 

So...While driving around today a thought came into my head...Suppose one was to take a block, mill the deck area down "except the cylinder bores" say .100" and mill corresponding bores into the cyl. head, so the cylinders would be stabilized by the head...perhaps with a copper O-ring in the bored area for sealing? Calkins dragster photo above, got this in my head...Thanks!

 

There's been a lot of discussion about this many pages ago in this thread. The cylinder girdle I suggested that's similar to what the Honda guys did a long time ago seems to be the favored solution for stabilizing the cylinders and probably the best option. IMHO

 

According to my Connecting Rod Manual the big end should measure 2.6522 - 2.6530". This is what an automotive machine shop uses to resize the rods.
I might be dumb, but I don't find that spec in the Mercruiser engine manual.

 

Little benefit and much additional complexity vs a traditional O-ring and receiver groove setup.

You've mentioned this several times. Can you ballpark a price? It's well within your capability to whip them up if people want to buy them.

A ghetto one-off solution would be to cut the deck surface out of a stock iron 460 head and then cut out just enough that it "drops" in with only the slightest interference that can be overcome by hand.

Which is exactly what I have so I guess I'll just buy OEM bearings and pray. The thing presumably went together just fine 30yr ago using OEM bearings...

It's not in the table section it's in the connecting rod section on the actual page with the rod. The whole manual has a bunch of info similarly buried like that. Stupid IMO

 

There was at least one person that made several of these and already has a CAD file for them. I'm not sure who it was without looking back over the thread. But it's not too far back in thread from what I can remember though....

 

Except for the 460 part being iron and the 3.7 being aluminum.

 

Iron should grow less than the cylinders so the fit should remain tight with heat.

 

Well, I was told I will be the owner of my first 470 about Dec. 15, salvaged from a rotted boat.. not frozen, "ran when docked last"...we'll see. $250 and 100 miles to get it didn't sound bad. When running and prepped for road use, it'll be going into a Willys Jeep.or truck. And modified from there as deals come along.

 

The fuel pumps listed as fitting the 3.7 along with a multitude of other engines don't fit. The lever arm is wrong. I knew that going in but was hoping that it would just be a stock photo and the actual pump would fit.

 

This seems to have been one of the deepest rabbit holes to be discussed in this thread. A lot of good ideas, some seem to be feasible. The best solution is the one that the average enthusiast can can do with the basic tools they have at home. Not everyone has a mill or lathe at home, or even has friends that do either. So that leaves, I'm my opinion, the cylinder girdle as the best option for several reasons. One, its tried and proven to withstand high cylinder pressures from insane boost levels without failure. In the nearly 25 to 30 years that the early Honda racers and enthusiasts did this, they achieved 1200 HP and beyond with relative ease. Second, it requires no fancy or expensive tools, no special machine shop labor to install, and anybody can do it with basic hand tools he or she has at home. So yes, there is always going to be attempts to make a better mousetrap, that's just part of the hot rod culture. But don't overlook the ones that already work, so I think it provides the broadest and easiest solution for those reasons.

 

I don't remember who posted it, but here is the deck filler. You'll have to search the thread for the file to download. Send the .dxf file to a company like SendCutSend, they will ship you the part, use a file on the filler piece until it fits into your block, at or below the deck, put your head gasket on it, and see if you need to drill coolant holes in the piece (I have no idea if you need to), and use green Loctite (sleeve retainer) on it. Done deal.

If the deck filler is really tight in spots, or you force it into the coolant passage, it may put pressure on the sleeves and may move them (unlikely). If you weld in the filler piece, you will warp everything and move everything. It does not matter how good of a welder you or your friend thinks they are, don't be full of yourself.

 

I completely agree and would gladly spend $100 on a girdle if one were readily available.

edit: found the dxf earlier in the thread. Not sure how I missed it the first time.

This is the post: The elusive 224/3.7 MerCruiser banger

Credit goes to Three Widows Garage

 

$200ea in 6061 and $140ea in 5052 from SendCutSend. I'm going to investigate lower priced options...

 

I can make some samples from the file posted. One issue I see, because I deal with this all day long in the CNC world, is the file is going to have to be tweaked to get the right fitment in the block. Since the company cutting these out doesn't have a block to test fit the part too, its either going to be loose or too tight for some blocks.....

 

Funny, I was just about to post the file to IBB asking if anyone with a CNC wanted to whip one up.

Questionable fitment is par for the course when it comes to these things. We're dealing with the rough parts of a casting after all. The commercially available ones seem to be manufactured "good enough" and the user is responsible for using good judgement and making adjustments if needed.

 

Yeah, I'd like it to be a little on the snug side and be able to hand fit it to the cylinder barrels and inside walls of the block.