The elusive 224/3.7 MerCruiser banger

I haven’t leapt off the diving board yet--I’m a little concerned about the Mercruiser’s durability in every day street use; witness Dennis G’s blown-out cylinder/detonation/camshaft problems.


My build would be much like his—torquer cam, probably .030-over (or more), etc. Basically a stocker, rebuilt, updated. I would go zero deck and aluminum head with plenty of squish and flat top pistons and crank-triggered ignition.


Why, though, is he getting detonation at sub-9 to 1 compression? Detonation bad enough to pit cylinder walls, leading to splits? After backing off on the timing? This really worries me, sooooo…

(He starts a-thinkin’)

...First thought: All-American Cast Iron classic—it blows up? MORE CAST IRON! Ford built a 370 CID, 4.05” bore , a variant of the 385-series …I GOTS IT! Sleeve that sucker down to 370 bore size (4.05"), lotsa good FE-390 pistons out there (4.05"). 4.39 down to 4.05, let’s SEE that monster eat though a .170” -thick cylinder wall of good American cast iron!


2nd thought: OK, now I’ve decreased CID and bore size and not solved the detonation problem and probably introduced a valve/cylinder bore interference problem, but at least I’ve spent a ton of money sleeving an aluminum block with an existing cast-in cast iron sleeve and not begun on the open-deck/earthworm-like cylinder conundrum. But what if…


…I sleeved the quivering thing down to a 4.25” bore size? Lots of pistons out there in that bore size. Sleeve itself wouldn’t be quite so thick, but BBC pistons and rods...

...And did a BossNine Brian-style deck closure?


Eddie

 

Dennis, reading though your previous posts, I really think your problem starts with the old open-chamber cast iron head, which was sort-of OK-ish for the marine 4,600-RPM fast-cruise steady-state fully-loaded usage Mercury Marine intended. A four-cylinder engine with its 180-degree is power stroke is wonderful for that. Tractors, too. And a couple zillion HondaMisubishiToyotaSuburus, too.

In the late ‘40’s, Detroit began building wedge-chamber OHV engines, the idea being that CR could easily be raised, 12/1 or higher. These were small chamber heads, lots of squish; Detroit continued on this path ‘til the ‘70’s (late ‘60’s?), when the emissions gods decreed “low compression”, which meant Open Chambers. It also meant an decrease in cam and timing lead.

I think the Chevy Vegematic pretty much proved the aluminum block/iron head didn’t work really well; Mercruiser’s went on to drive that point home when they cheaped out and put an open chamber detonation-prone head on their four-cylinder aluminum-block.

Electronic Fuel Injection is precise enough emissions-wise that Detroit and the aftermarket has returned to closed-chamber head designs, high-squish head designs. High-squish means high-turbulence, which leads to less initial spark lead, which lead to lessened detonation proclivities.

Kaase's P-51 is gee-whiz cool, 2.2" valves 'n' all, but it is designed for a big cubic-inch high-rev engine. Personally, I think the smaller-valve eBay head, carbureted or EFI, is the way to go for street/strip use.

Eddie

 

Yes, you need studs with a much longer block end threead length. Carrol Carter at C&C has them. Prepare your needed dimensions, phone his receptionist (wife?), he'll measure the ones he has around. Thats what I did for my Kaase Boss head.
Short threads would likely pull out of the block. I would not chance it.

I also had my studs set up in a lathe and the unthreaded portion cut down to .50" diameter for greater stretch.

 

Thanks iadr. I did a search and found the Carroll Carter Motorsports site. Looks like a very serious Ford performance place. I was not aware they existed.

 

I will get a better photo later. You almost can't tell it is a 3.7 with the side shield, fuel tank, and big air cleaner.
This one has a Cobra Jet head, mechanical Engler methanol injection, relocated ignition, and all the best parts. It is based in central MO. The owner/driver has not been able to get near all the power to the ground. He has been detuning the motor to try to let the tires hook up. If you are near central KY (Powderly) and want to see and hear it, come to the tractor pull there (Fri and Sat). This is probably the nicest "Outlaw" garden tractor in the country. The same guy has another nearly like it with an Esslinger Ford in it.

 

Don't worry about the 470 for street use...It will be fine.

Detonation had nothing to do with my burst cylinder.....carburetor leaked and that engine hydrolocked and burst its lowest cylinder.

Yes, there was detonation, but I found a cam grind that does not detonate.
I had some lobe wear, changed out the reground cam for an Elgin cam that caused serious detonation. I have since had my Elgin cam reground to the non detonating profile.
My current block was over-bored 0.009 by the shop and they are redoing it (free).
As 040 over pistons were available with a 23cc dish, I went with them following big chief's advice. The cam profile I like is a supercharger cam and I bought a M90 supercharger so it should all work.

Dynamic compression ratios are the ones that matter, but if we go from cylinder pressure measurements, at 165 psi (cranking) there were no problems but it went up to 210psi
with the Elgin cam (a 27% increase and way too much for 89 octane gas so its timing had to be retarded 4 degrees). My records show a 9.2:1 static compression ratio with 100cc chamber iron heads. that equates to about 7.9:1 dynamic c.r. The 23 cc pistons give a static c.r.of 7.7 and a dynamic c.r. of 7.2:1
If the cylinder pressure increased 27% more and if that relationship applies to dynamic c.r then the original dynamic c.r. should increase roughly that much from 7.9 to around 10:1 so no wonder it knocked on 89 octane with the Elgin profile. It was a zero decked engine which increased the compression a little over stock, for the purpose of increased combustion chamber turbulence, reduced fuel stratification and reduced knocking. I should be able to adjust boost pressure to increase the lowered cylinder pressure by changing drive pulleys and gain some power.

And yes, the Ford iron heads are not so good, but they are cheap, common, really heavy and more prone to knock.

(I know I've played fast and loose with my rough estimates above, they are no more than crude approximations)

 

Dennis, thanks!

Guess I misinterpreted that infamous line, "...I burst a cylinder 2 years ago so cylinder strength is of paramount importance to me. The cylinder burst keeping the rod from bending. Analogous to an expensive transistor blowing to save a cheap fuse..."

Thanks!
Eduardito

 

The first tires I tried would not hook up either. Hit the throttle on dirt and the car was sideways but not going any faster. Even on pavement it needed different tires. Once I changed them it had much improved acceleration

 

My first engine's cam was a supercharger grind and it did not knock on cheap gas. It wore and I replaced it, but its closer to stock replacement knocked noticeably at idle so I had three cams reground to the first cam's profile.

I bought a used automotive iron head for my first engine. Not knowing that Mercruiser mills the side of the intake side of the head narrower to match the block, I had to make a cork gasket to seal the head and block to the intake manifold. It was the only gasket material that could seal that much width difference and it works fine but cork should be re-torqued occasionally.

 

For those wondering why marine cams knock, they have early exhaust closing so water does not get sucked up exhaust as most exit underwater.

 

I've officially joined the 224/3.7 owners. Picked this up for $100. Obviously needs work.

 

Glad to have you with us. We have a lots of information posted here so you will not lack for that.
I've saved engines with uglier bores than yours, but you are limited on how far it can be bored as the cast in sleeves are not thick.

If you did not get a good head with it, A big block ford head will work but is so wide that sealing on the intake manifold is difficult unless you either use a soft cork gasket or mill the head's intake gasket surface to match the block's width. Mercruiser heads have a water tube the factory adds . You do not have to do it their way. I drilled the intake manifold flange for water movement to the radiator from the head. I posted photos of this several years ago.

 

Thanks Dennis. I didnt getba headvwith it but did get a 2 barrel intake, and the bores are standard size right now. I'll be checking out the whole thread. Joe

 

good, I thought he owed you more than what was in the picture so I'm glad there is an intake manifold. It is a good heated manifold and will take either the usual carter carb or with an $11 adapter a Autolite 2100. The least overbore that works may be best.
My latest engine had a std bore and was good except for one rusted cylinder I had some .030 over pistons so it was bored to that, but he bored one cylinder .008 too much so he offered to do the job over again and i bought a set of .040 over pistons. Before you bore the cylinders, check piston availability and price. Both vary widely.

 

Dennis, thanks for the advice. An $11 adapter or a piece of aluminum from work with a bit of machining. Which model of Carter would that be? Thanks, Joe

 

Joe:
the inexpensive adapter sold at auto parts stores is what I use to put an Autolite 2100 (a favorite carb I've used for 52 years ) on my 2 bbl manifold.

Rochester 2GC 1708 1060 is the common carburetor. Mercruiser supplies their own version of the 2GC . it differs in having a single idle mixture screw.

jets and power valves are easy to find for Autolite
I use a wide band O2 gauge to choose jetting.

 

would anybody be able to tell me what ci and year and any other info on this engine?
https://inlandempire.craigslist.org/pts/d/mercruiser-4-cylinder-motor/6390990111.html

 

This motor looks to be one of the Chevy 4-cyl based MerCruiser items. The little aluminum 'tag' on that flat spot on the front left side of the motor is your friend : If you call MerCruiser with that serial number, they can supply you with cubic inches, horsepower, year of manufacture, etc. You may have to try several MerCruiser sites to find one that will talk to you, because they want to SELL you a replacement instead of GIVING you information! Don't give-up, just try another number, & eventually someone will help you. That's what I went through with my "488" motor

 

it is either the Mercruiser 120 or Mercruiser 140 engine which was originally a mid 1960's Chevrolet 4 cylinder Chevy 2 engine. The engine was also in late 60's post office Jeeps and has been used in a huge number of forklifts. It is still made as an industrial engine. A lot of smaller inboard powered boats have this engine OMC painted theirs turquoise blue and Mercruiser painted theirs black. The aluminum valve cover and black paint is positive identification as Mercruiser. The greatest problem with them is that they were run with seawater (or freshwater) cooling. So they can have massive internal rust problems. Their displacement is 153 cubic inches and claimed power was 120 or 140 horsepower. It has 5 main bearings. The 120 has 3 inlet openings in the head and is a mid 60's to 70's engine , the more recent 140 has 4 openings, they are taped over in the photo and not visible.
The worth of the engine depends on how much rust there is. Rust pits can go entirely through the cylinder and the engine can have good compression. In that case it has to be sleeved.
The 120 lacks power (I'd estimate 90hp as being realistic) because of intake passage restriction in the head.
Fork lift wrecking yards sell the motor and it will not have internal rust. There is a forklift yard in Portland Oregon. Automotive wrecking yard motors will not have the rust problem either. It is cheaper to buy a running engine than to rebuild a rusted one
Buying either a 120 or 140 is a gamble because of rust. In the engine for sale, the thermostat housing is off so you can look right into the head to see if there is much rust.

 

There is a free one of these in Edison NJ on Craigslist right now.

https://cnj.craigslist.org/bpo/d/mercruiser-470-engine-37/6404082916.html

 

Why can't someone near Detroit give one away?

 

Look in boatyards, they don't like rebuilding engines. You may even find a free engine, but a free engine can end up being quite expensive if you want to run a parts engine. The first engine I bought was $100 and had a freshly reground crankshaft still in its box. I bought it for the crankshaft, new starter, manifold, oil pan and block. The rest was junk. (What it cost is detailed in a post several years back). I could have bought a good running engine for its final cost but would not have learned anything that way. Expect machining expense on the head, block, crankshaft and cam. Try not to throw money at it. Watch out for cracks, rust, wear and old botched rebuilds.

 

Thanx Dennis,

I see them all the time here on CL. But, instead of cheap, these are made of unobtainium.

Really, I'm looking for a rebuildable short block. I have one piece already, forged crankshaft, standard on both rods and mains.

This is way down my list of things to do, so I haven't done the legwork to REALLY find one.

 

Boatyard guys often don't like working on these engines. So the boatyard is the place to look.

 

The rear main bearing cap has its sides sealed to the block with rectangular neoprene inserts. There are slots in the side seals that can take a pin driven in to expand the side seal in its slot. The pins have a .090" diameter. In my case I made two of brazing rod but they bent before I could get them in all the way in.
Now my question, are the pins really necessary? I'm using locktite 518 gasket maker to seal the rear main cap.

 

Big Chief you still there? I was wondering if you could help. I have a 1981 Boston Whaler. I replaced the head gasket, set the timing as per the book at 8 BTC, installed a Pertronix solid state ignition, and a Edelbrock 1409, (600cfm). Rochester was re-manufactured junk. Used the jet setup they sell for the 4.3. It takes off OK but seems to be down on power and slowly gets too hot. Does not have any problems at 1500 or below rpm. Water pump impeller on outdrive is new also. Opened up heat exchanger and it was fine, no blockage. Driving me crazy, any ideas would be greatly appreciated. I'm using a relay on the Pertronix to get full voltage to the coil. That was a problem.

 

Mark, a known issue with this engine was the poor timing retard "fix" that Mercruiser used to get around its detonation problem. Retarded, the engine ran hot and had less power. Big Chief's cure for it was to change out the flat top pistons for 22cc dished low compression pistons and advance the timing. With retarded timing, the engine runs hot and makes less power so check if your distributor is advancing properly. The piston change reduces its compression ratio from 8.8 :1 to 7. 7 :1 and in Big Chief's words "wakes the engine up when you reduce the compression ratio and advance the timing to where it should be". I run my engines advanced 32 degrees at 2200 rpm. Alternatively, you could use 100 octane aviation gas and advance the timing.

 

Thank you I will try that. 93 octane is the best I can find here. I will run over to the airport and set the timing as you recommend. Sorry for hijacking the thread

 

I am debating about filling my block. For those that don't remember, my motor will be a competition piece. I was not planning to run water anyway.

A friend bought a couple of these motors when he was building his competition motor (post 1777 for photo). Several were cracked at the front of #1 cylinder and the front web. He believes this is the week spot in these engines. He filled his block. I am wondering if this is where they break if they freeze, but not a strength issue during operation??

Recently another guy using one stuck #4 rod out the side. He destroyed everything inside. That wasn't caused by block issues but a rod issue. I had an extra block for him but he is still needing a crank.

If I decide to fill the block I am wondering what to use. The common block fill material has iron filler in it. That makes sense for an iron block, but not so much for an aluminum block. I have that here in bulk. The other option is epoxy with aluminum in it. That gets very expensive if it is purchased premixed. Epoxy is about $5 a pound if you buy bulk. Aluminum powder is cheap when purchased by the pound. My wild guess is epoxy weighs about 10# a gallon. Another option for the aluminum is waste from a machine shop. I have access to all of the aluminum milling chips I want. I would need to clean the coolant residue from them.

Anyone have suggestions?