The elusive 224/3.7 MerCruiser banger

I would throw some red loctite at it and worry about more important things.

 

A distributor would not load the end stud nearly as much as a water pump.

I usually run a cut off cam and plug the hole in the aluminum casting where the stock cam would go through it.

A minor difficulty is that to mount the cam between centers for regrinding, it is easier to have a hole in each end of the camshaft to center it. A new center hole can be drilled in the cut off end.

Although the stock waterpump is nice, consequences of leaking antifreeze into the oil behind the water pump are serious and the cam wears faster than I expected under the seals. A distributor mounted there instead of the water pump is safer and an electric waterpump frees up a few horsepower that you may want to use for propulsion.

The disadvantge is that electric fans and waterpumps and starters (20 lbs) need a 40 lb battery in the car.
There was a time in my life when I looked for little hills to park on so I could have a rolling start. Alternator size may be so small for lightness(6 to 11 lbs) that after 15 minutes headlights become too dim to be of much use so one quickly learns not to drive at night.

You may get by with a starting capacitor (1/2 lb)and a 19 lb garden tractor battery (I never tried a garden tractor starting battery (with capacitor)for a 3.7 Merc). But a starting battery cart would work if it didn't.

Besides, the adventure begins when things don't go as planned. Life is full of adventure.

 

I am so disappointed with my dyno session today. My motor isn’t happy. A wheel dyno was being used so there is driveline loss to consider. It only made 128 hp and 131 ft/lb of torque. A stock motor makes more.

I have no issues with the tuner. It is the mechanicals of my motor causing the problems.

It hits a wall at 5200 rpm and won’t go any higher. We aren’t sure what the cause is. It could be a combination of several things. The MAP sensor output gets very erratic. It is bouncing all the way up the rpm range but it really gets unstable at around 5200 rpm. The intake is seeing pulses from each cylinder. The air cleaner now has holes in it from heat blowing back.

Possible causes:

1) My intake isn’t suited for the application. I have short runners (about 6”) leading to a plenum. The tuner spoke with a 4 cyl. comp dragster guy who had the same issue. He resolved it by installing stack injection and eliminating the plenum.

2) The lifters are floating. I’m using flat tappet hydraulic lifters. We did play a bit with them, tightening and loosening with no help.

3) The cam just isn’t big enough. It was recommended to install it at 109 deg initially. I set it at 111 deg when I was having the high cranking pressures, which are still at 215 psi.


On a good note; the MLS head gasket is holding! No water leaks. After starting it sounds good until it hits that wall and breaks up.

It still wants to kick back when starting. Something is going to break.

Possible fixes;

1) Make/modify another stack injection intake.

2) Change to solid lifters

3) Have another cam ground that has more overlap and lift.

I am near my limit with this motor. I'm close to throwing the towel in. I have been working on it for over 6 years. There is something to be said for belly button motors. There are proven performance formulas for them. Not so much for these.

 

Beck,
I've been waiting for your post on this. The results are very disappointing but maybe not as bad as you think.
The erratic MAP output suggests to me that maybe you are seeing a valve spring problem. This along with the 5200 rpm wall would lead me to try some stiffer springs. If you are not too close to coil bind, maybe just try some .060" shims. Might not be the ultimate solution, but should quickly show if that is an improvement or not.
That cam is not all that radical. While pulsing in a 4 banger is going to be greater than a 6 or 8, I believe that your problems are not strictly due to pulsing.

Can you extend the intake tubes easily to see what difference that makes?

We're rooting for you!

Have you checked with Chris Nichols for his ideas?

 

I had not considered the springs. I have heavy ones here, but too heavy for flat tappet cams.
The cam is really mild.
The pulsing is what burnt the air cleaner.
My intake is fiberglass. It won't like that much heat either. I could cut the runners off to lengthen them but they are tapered. That would put a straight section in them. I really hate to whack it up.
I was hoping Chris would check in here. I may call him.
The tuner called on another 4 cyl comp drag racer today. He said he had a motor that did the same thing. He solved it by putting stack injection on it instead of a plenum. I'm guessing he was using mechanical injection. I don't know what throttle bodies I would adapt for stacks. (Motorcycle or Weber style) I am currently drive by wire so all of that would need to be swapped out for mechanical cables. The wiring harness would also need to be changed for that. From what I read it is best to tune with Alpha N with that type of system. I currently am not. So, lots of changes consider. I think this project is going to get moved to the back burner for a while. I am upset with it.

 

With so many unknowns in setting up your engine, you must feel your way along, and that takes time. You have shown great perserverence in this and you have made useful contributions to our knowledge.

At 215 psi it is cranking and starting.................success
it runs with all of the changes that you made ...success
the steel headgasket does not leak.......................success
you did not mention vibration problems............success

You have made complex changes so the number of introduced variables is high. It will take more time to find the problem. Only make one change at a time and test the engine after each change. That is the fastest way to proceed in uncharted waters.

Some in this forum have experience with getting high rpm from the mercruiser 3.7 Randy I believe ran many of his to 6800rpm. You should contact him. The guys who race these engines seem to do ok with their rpm.


Used camshafts are cheap, you might grind one at 109 degrees but grind another at 115 at least for comparison as it has been suggested so often.
Solid lifters are less frustrating for me. I'd try the easiest first.

 

That will get pretty costly. I paid $800 for yesterdays tuning session. Plus the $175 of diesel to get to and from there. It doesn't take long to spend a grand anymore.

 

Rule those out right off the bat. An engine that's running out of cam or with an ill-suited intake doesn't flow back through the intake.

Erratic map means erratic intake vacuum. Yes, 4-bangers pulse, but even 2 and 3cyl engines don't pulse enough to damage air filters. At 5kprm the only way intake vacuum can be erratic is if lots of air coming from somewhere... like an open intake valve.

 

Beck, I was hoping you would post results but like you not what I was hoping for. I expected intake pulses is why I went with the long injectors I have. They are about 15 inches from butterfly to the intake valve. I can play with bell lengths to add torque. From my dyno work with V8's that's what seemed to work the best. My engine is assembled now and seems to have a lot of compression, I think I will go hook up the starter and get a cranking compression. I have my cam in at 115.5 intake centerline and was told I will have to use premium gas at that. I also had it changed to a solid cam, but now thinking on it and what this engine might have for expansion, that may of not been wise as I plan to drive on the street. Your short course use, I would go to solids. Sorry to hear you are still having troubles, but keep at it, you have a impressive rig!!

 

Wouldn't fire in the intake have to come from the cylinder through an open intake valve?
Could you adjust your cam timing so the valves open later?

I have a 2 stroke single ultralight that blew fuel out the carburetor until I extended the intake a foot beyond the carb..
It suffred from a port timing change that did not go well. (I'm innocent.)

 

That is worse than awful.
Assuming you have no differential on your tractor, could you cobble together a hub dyno to get an idea of torque comparing one test to another.

 

Your engine sounds somewhat like mine. We use the same lobe centerline. However I use hydraulic lifters. With the right cam profile (which the boat profile was not) it is nice to run on the street. With high compression and the wrong profile it ran hot and detonated even with no load on the engine. I don't remember using premium fuel in it but that would have helped, but I had the cam reground (It solved the detonation) but it still ran hot (about 400 degrees too hot), now after changing to a set of low compression pistons it is running cooler.

 

DennisG,
I have 11 to 1 pistons, but my cam grinder told me I have options on setting lash and where I degree it in at will determined how much compression it will make. Static is 11 to 1 but dynamic is 8 to 1 as set now. I have small chambers in my head. Quench is a little loose because of my aluminum rods but I plan to try it as is. Probably a month away from start up then we can see how it will be.

 

Closer inspection of the air cleaner showed it was not heat/fire that destroyed it. The pulses were sever enough that they tore the filter media from the screen it was embedded on.

I do have a differential in the rear axle.

 

Always try it before making changes. Always.

 

Years ago in these posts, insufficent lobe centerline was mentioned as a cause of pulses.

 

What application do I order front and main rear seals for? 351C?

 

I don't know of any 351C with a one piece rear seal. Maybe a late model 351W with a one piece rear seal, but you still need side seals. The front, I don't think any stock Fords will fit.

 

Summit sells Mahle gasket sets for these engines.

 

They do. But they are very, very, expensive for what they are.

I was just guessing on the application since the mains are 351c and the flywheel is Ford.

I may just have to measure the parts and just fine something that fits the dimensions for the rear. It's just a seal after all.

After digging around in my parts pile was able to get a part number off the front seal. CR18912 (so Chicago Rawhide 18912) which is a Chrysler 8.75 pinion seal.

 

You must be a Chevy guy. I thought $19 for a rear main was pretty reasonable.

 

So, cam/water pump seals....

Google says part number is Mercruiser 26-97530. Amazon lists this.

I think that ID number is wrong. My micrometer says that the camshaft with the stud to hold the water pump impeller on, like pictured on the last page has a .875od on the snout. I assume that the Amazon listing is just wrong and that the seal itself is the correct one. I measured a front cover and confirmed that 1.500 is the correct size. I also measured the seal I took out and it was .305-.310.

Nevertheless, this is a standard enough seal and I was able to find a compatible seal on the SKF site 8707. (I have no particular preference for SKF, they just had the easiest to find "search by dimension" tool. There are other seals that fit here but I restricted my search to FKM/Viteon seals because the temperatures inside an engine being worked hard is pushing the limits of the environments in which you can expect a good service life out of a nitrile seal.

 

If I could have found a good complete top and bottom end gasket kit for $100ish like you can with most 4-6cyl engines we wouldn't be having this conversation.

I was looking at the complete gasket sets on eBay. $150 for a head gasket set seems kind of unreasonable when a head gasket set for a SOHC V10 costs $16 more. I know it's "boat parts" but come on.

Several eBay sellers list the 3.7 gasket as also fitting a Ford 351 so and 1987 up uses a different rear main than '86 down so I'll probably order the early style for $7 and cross my fingers.

 

Early 351w will be a two piece seal. I have my old rear seal I will measure it up and see if it fits the later 351W. I bought just a lower gasket set for mine. It was about $100. It did not have any cam seals or side cover gasket. So 100 bucks for a pan gasket with front and rear seals and a front cover gasket. Not really worth it!

 

It looks like a 351W rear seal is the one. I compared it to one in a block and seems the same. The part number on my old rear seal is YSK 46838, front seal I don't recognize is a Victor 49230 and a cam seal is CR 503128. These are numbers off my old parts.

 

A later one piece one? Like for a 90s truck.

 

Yes the later one piece. 90's truck should do

 

Don't forget to get the two little rectangular seals that go to the sides in that area. They don't survive reuse very well.

 

I always make the pan gasket, side cover gasket and front cover gasket. It is easy and the cork sheet does not cost much.

 

How about this one ? not mine.... https://bid.bid-2-buy.com/ui/auctions/79028/7942986