The elusive 224/3.7 MerCruiser banger

Permatex aviation form-a-gasket is now sold boxed as perfect seal at tripled prices. It is not perfect seal and does not seem to be like perfect seal.

 

The black oxide coating on headbolts prevents rust if it has some help from oil, but oil runs off. Wax on it works but it runs off in heat. Paint stays on. There are three different proceses for making forms of the black oxide coating. It is durable but is removed when a scotchbrite wheel removes the rust. Once the bolts rust they have to be replaced or if the rust is shallow, remove the rust and paint the bolt. Painting the shanks of new bolts is ok if done carefully.
The black oxide can be replaced by using a $50 chemical kit .

 

General advice: if you are going to use a 3.7 mercruiser engine, get two of them.
Begin by making a stock engine run well. Then you can try your innovations on the second engine, preferably one by one. That way your chance of success is greater.
Although it is a good engine, the 3.7 has innocent appearing quirks that can prevent it from running. In particular, cam profile and compression ratio can cause massive problems. Although not high, the stock compression ratio was for the higher octane gas that was common 40 years ago. One can run E85 and get around that problem. Its cam profile, iffy to begin with, combined with high compression can result in overheating and detonating.

 

I like msd distributors but they don't make them for the 3.7. so I made my own, well sorta. I bought cheap off shore stuff to see if it will all work. This is what I came up with.

 

How about a step by step tech thread on the distributor modifications? With pics please!

 

I didn't take any pictures, but here is what I did. MSD makes a VW bug dist, so I
I bought a bug dist from I believe was Southwest auto on ebay, $69.95, then I bought a small block Ford, $124.95, from the same for the shaft and housing. Both MSD knock offs. The bug dist is to short and to small od. I thought about sleeving it like the Merc but still needed a longer shaft. The small block Ford housing is I think .030 larger then the Merc. So turned it down to Merc specs, shorten it, made a slip ring to set depth. Bolted the upper and lower together. The shaft parts are .500 and the Merc gear is .470ish, so reamed the gear to .500. Slipped it all together, set end play, drilled and pinned the gear on. I can take pics later of the old parts, I'm sure it will explain it all a little better. Not knowing if it would all work and taking my time to make sure it would, I had about 5 hours in putting it all together.

 

Here is a pic of some of the parts. The top shaft and housing are MSD small block Ford, the bottom is the bug parts I did not use. I only used the shaft and lower housing from the Ford dist.
If that don't explain things, I will try again. I don't have a second Mercruiser dist, but am gathering parts to make another one.

 

Thanx Flatrod,

You are a true Hot Rodder.

 

I usually bought rebuilt 4 cylinder Delco distributors and swapped in used Mercruiser parts as needed to end up with a fresh Mercruiser distributor.

 

Today I found that mercruiser 3.7 engines do not all have the same flywheel.
I opened up my 488 to find instead of the Ford flywheel a boat flywheel with smoothly rounded corners and with no holes for a pressure plate. My other two engines, a 470 and a 170, came with stock Ford car flywheels painted Mercruiser black. (they are mid 1980s flywheels used on manual transmission small block ford engines).

 

I only have the one engine, a 470. It has bolt holes and was going to use it, but I found a steel 157 tooth aftermarket small block Ford flywheel in my pile of parts, took the bolt on weight off to use it. They both weight the same, 23 pounds. I have balanced everything, its all ready to go.

 

Warning: Speedmaster cylinder head studs for Ford 429-460 are made wrong.
The factory rolled the fine threads too far down the stud and only rolled the coarse threads about half as far as they should have. The studs they made will pull out destroying your block. The picture shows a speedpro stud and a Frod (mercruiser) headbolt the stud is reversed to show how the threaded sections lengths compare. The speedpro thread only engages 75% of the amount of block that the Ford stud engages. This is serious and made more serious as die cast aluminum has about 1/3 of the shear strength of grade 50 grey cast iron.

Another error in them is that the shank of the stud is too fat at 0.558 inch. This results in a rigid bolt that breaks instead of flexing. When a bolt breaks it is often in the threaded part near the beginning of the threads where the stress on them is the greatest. A fat bolt breaks before a more slender one which flexes in length. Volkswagen discovered this decades ago.

Stock Ford headbolts have 0.500 inch diameter shanks.
The proper diameter of the fastener shank will not exceed the minor diameter of the threads (0.480" as I measured it). because if it breaks, you don't want it to break in the block where the threads are. That diameter may be too much as it may need to be more slender to flex.

 

Good. As far as I can tell, it is an internally balanced engine. Good that you took off the weight.
Now for a story : A close friend raced in competition where the engines could be claimed. He had a good engine that was claimed by another racer who complained a week later that it shook his whole car. Dick purposely made an externally balanced engine to discourage the claiming of his engines. The flywheel, never included with the claimed engine, was where Dick balanced it. so without its special flywheel, it was not a useable engine.
Dick used big block Ford engines as the competition used small block chevy engines and Dick's engines would not fit their cars making claiming less probable.

 

Oil temperature matters in choosing oil viscosity. An oil temp gauge is needed to make use of the following chart.

 

Oil information from the internet on the oil that I use:

 

I'm looking into building a 470 for a future project like a little nissan or something similar that's small. I've read through the posts and tried to understand as much as I could but I think this is going to be a read as I do kinda thing. I've done engine swaps and mods over the years so I'm not totally ignorant to a project like this but my memory is a little fuzzy due to a heart surgery. I'm on the coast so I should be able to find a boat yard with what I'm looking but as I've read... useable blocks are hard to find.

I'm willing to put in the work for such an odd engine... I just hope this doesn't end up being a $5k build lol. Doing a build like this will give me a chance to play with carbs again as well if I don't decide to put in the work to figure out a EFI set up for it. I'm just spitballing at the moment but I do plan on contacting as many people as I can to get ideas and experience to help with a project like this.

I will start looking for an engine as soon as I move in a couple months and go from there. Are there any other groups I need to know about that are building these for land use? Any places that sell parts to help with what I'm trying to do ?(I understand the BBF head and high perf aftermarket head)

I'm thinking about setting it up to run a 700R4 or something similar and maybe 3.73 gearing. I've been looking around on YouTube to see if I can find one running with a open header but nothing much yet.... maybe I'll get lucky.

Advice and tips are welcome.

 

Welcome!
There are a couple of Mercruiser groups on FB that are mostly boat oriented. But, one that is for landlubbers is: https://www.facebook.com/groups/431992443615823
They are not too active but there is good info there.
I find this thread easier to follow and probably more directed at what you are proposing.

I have had my best luck in finding engines on FB Marketplace. Be sure to check out boats that are up for salvage. I searched for a couple of years on the auction site and Craig's list. Most were overpriced junk. Then I found 3 in a week, two short blocks and a complete running engine on Marketplace.

 

The engine can be cheap to buy, but it is usually a gamble even if it is expensive.
They normally run antifreeze which is a good prserver bt stay away from which just used water as a coolant (corrosion happens). One from a rebuilding company is less of a gamble but it would still need complete disassembly for the machining necessary to fit it into a car.
I kept track of what the cost of my first rebuild was and posted that early in this thread. I think it was about $3000 then which would be 3700 now and the boat shop said a rebuild was usually $4000 which after inflation would now be near your $5000 figure. With so many variables, the cost is unpredictable but can be lower.

 

I put a head on my engine today using locktite 518. Being anareobic there is huge working time. This engine is already in its chassis so getting the iron head in position on the dowel pins is a clumsy operation that would be much better with an electric hoist. Expect to have locktite smeared on your shirt if you decided to put it on metal instead of on the gasket. It was beginning to look like something out of Brer Rabbit and the tar baby. I used roughly half of a $14 tube of 518 sealant.

Something else, the dowell pins are very important but hard to find. I bought Big Block Ford dowel pins 6C3Z-6B041-A . They don't fit as they are too big but the length is ok so I enlarged the slot in them using a cutoff wheel and a file. They were 0.775" across and when they finally cut down enough to fit they were roughly 0.730".

 

What is the stock compression ratio? Seems to me that the detonation issue is likely more to do with the cylinder head used than the other factors. Ford's iron 460 heads of the era are not know for being performance pieces. I'd bet the more modern heads (in aluminum) are much more detonation averse at the same compression ratio even with the lower octane fuel we have today. But I could be wrong.

 

8.8:1, stock head has almost no quench shelf

 

In a comparison of the same 3.7 engine with the same head(iron), the only change was the camshaft. cranking compression reading:
cam 1: 165 psi , cam 2: 210psi.
At 165 psi the engine never knocked. (egt =1340F )
At 210 psi the engine knocked at idle until the timing was retarded 4 degrees to 28 degrees before tdc and it always ran hot retarded or not. (1740 F egt) unless the throttle was completely shut. The second cam was of use only as a cam blank for regrinding.

Yes , the aluminum head is much lighter, gets rid of heat better and someone wrote that it withstands more compression before detonating. The iron head is not good in several ways but every one of these engines comes with one so they are free. It costs enough to recondition an iron head that it is no bargain versus a new aluminum head.

 

I read this and like it. https://www.enginelabs.com/engine-t...ormance-squished-between-the-piston-and-head/
dennis

 

Sometimes I wonder why I keep trying.

I am still fighting with the 470 that has haunted me for the last several years. I thought I had it ready to go. Initially I thought battery/cable/starter issues. It is making so much cylinder pressure during cranking that the starter just cannot do the job. When the pressure was checked it was 280-285 psi while cranking. From what stupid me is told, that just won’t work. (Yes, the cam has been degreed and is installed correctly.)

There are a couple of options. 1) Cut the tops off the pistons. They have 24.2 cc domes for 13.6 compression for E85. 2) Install a thicker head gasket. 3) Install a bigger cam.

As you know with this motor there are issues with most of the options. Cutting the tops off of pistons would be a challenge for any engine. The 13.6 compression is right where it needs to be for E85. I really don't want to tear it down that far.

Head gaskets are a known issue and not all work as claimed. It currently has a stock Mercruiser head gasket. Cometic says they do have them available thicker. Solid copper gaskets are also available. This again lowers compression lowering the power output.

Since we still haven't found cam cores with gears buying a used cam, then have it reground is still the only affordable option. My current cam is a wimp. It needs a bigger one, so this is the route I have chosen.

There was 1 cam of my design left on Flee-Bay. It is now on the way to my cam grinder. $45 for the cam plus $20 shipping. I was way to lazy to look for another motor and disassemble it for the cam. Plus I would have filled the garage with the rest of the parts. I have forgotten what the regrind costs.

My motor is looking killer, but has yet to make any motor noises of it's own.

 

Beck,
Glad to see you're back at it. I'm curious about the lift, duration, LCA etc. on both your existing cam and the one you are getting.
Understand if you don't want to put this out to the public but it would be very helpful for those of us that are following behind you.
I agree that you took the only practical path. Lowering the compression is not a good alternative.

 

Beck, before you tear it all down try retarding the cam 4 degrees. But when you do be sure you check piston to valve clearance. This can reduce cranking compression by up to 20 pounds. Cam may not perform like you want as it will increase top end while reducing low end output.

 

I don't know about alcohol cranking pressures but someone posted here early that there is a gear reduction starter for this engine. https://www.qualitypowerauto.com/item_106/International-Starters.htm I assume you already have an ignition cut off until you get it spinning.

 

Here is the cam that is currently in the motor. This would have been fine had I not got crazy on compression ratio. With a smaller head and pistons on gas it would probably have ran well.

 

We haven't discussed the new cam grind. We have some concern as to how deep the heat treating is on the factory cams. That will limit how much can be ground off. Looking for something in the .245 to .250 intake duration at .050. from what I understand.

I wish I would have spent the bucks for some good rods now. The bigger cam will want to go to a higher rpm. The rods are my limiting strength factor. I have the stock rods with aftermarket bolts. I'm told 6000 rpm is as high as I want to turn them. I know others that have gone higher, but I don't want to redo all this. The hydraulic lifters my be the limiting rpm factor.

Flatrod17, I can't give up the bottom end on this motors usage. Once I have it far enough apart to retard the cam, it's far enough apart to change the cam. As much money as I have stuck in this thing already it's just $ signs going by. [I'm very interested in your distributor setup!]

34Phil, I have that exact starter on my motor. There is another one made by the same company that is larger, but still gear reduction. It has more cranking ability. Unfortunately the size won't clear my header or steering. I have spoken to the starter folks. They say the small one should crank it over. These starter prices keep going up.

 

I don't believe I have posted a motor photo for a while. Here is an updated one. This all has to come apart again to get the new camshaft. I had been torn away from this project for several months with knee problems. 1st I pretty much tore it up, then had to wait for a Dr. appt, then had to wait for a surgery date. Now I am 7 weeks past total replacement so I'm beginning to "play" again.
Click to enlarge.