Merc 420 Cyclone engines

[BDC1013]

Some of you may have read my story of inheriting my dad's 36 mirage, and my goal to get it running again.

I have one complete Merc 420 and was looking for a bit of help. This engine has not run in 15 years or so, so getting it going again is going to be my first step to see where I am at. If i can get this engine running I will try and find a similar engine to put next to it. If it barely runs, or does not run at all, I will strip it and sell it and find two matching engines.

I am looking for another matching engine and/or two engines to get this boat running.

Anyone know anything about these? I pretty much have all of the accessories for both engines except carbs (stolen) and one set of exhaust pipes (stolen).

Jeff (Old377Guy) Has spent some time with me and looked over the boat. He suggested I reach out to you guys for information and advise.

 

[BDC1013]

Been doing some research, Jeff told me i have #3 drives. I believe i have the mercruiser #3A speedmaster outdrives. Only thing missing from one on the drives is a hydraulic ram (stolen). I think thats about all the parts that were stolen. Hopefully i can find a used ram for a decent price.

 

[MOBILEMERCMAN]

The 420 and #3 was about 40 grand option back than. Great combo. Good trannie and damper pieces. Nice bellhousing coolers, likely has rear engine plates. Had to have external steering. It will be something special when you get it going.

 

[old377guy]

Exactly so Jim, the boat is VERY straight, clean and has some great old hardware.

 

[600sci]

#3 not 3 a's...not with 420's but rams can be bought on e-bay, foud a guy that has several for cheap !

 

[BDC1013]

The 420 and #3 was about 40 grand option back than. Great combo. Good trannie and damper pieces. Nice bellhousing coolers, likely has rear engine plates. Had to have external steering. It will be something special when you get it going.

Thank you, I was hoping you'd chime in... Jeff had mentioned you while we spoke. I was reading about these drives and it seems they can hold some serious power. I believe the drives still have the clever style props on, which i saw a pair online going for around $1000. I also saw some #3's going for around $5000 so im glad no one stole these drives while the boat was out in the yard for 10 years.

I'm hoping to find an arm, lube these things up and have no problems with them.

 

[BDC1013]

#3 not 3 a's...not with 420's but rams can be bought on e-bay, foud a guy that has several for cheap !

I was looking at some pictures of 3's and 3a's. Some say they all look the same from the outside, but i did see a few different pictures for each so I am not sure. Also i read that you can tell the difference by the hole in the case that the rear trim cylinder pin goes through. A #3A uses a 1" pin and a #3 uses a 7/8" pin. Might be something worth checking.

 

[BDC1013]

also i was looking to find some replacement exhaust pipes for the port engine, YIKES! i came up with Gil exhaust for what I think I have on there now. Not cheap. Might be easier to sell the riser set i have and find something a bit cheaper for both engines. I have both sets of the manifolds so i should be able to resue them as long as there aren't any cracks that i read about for these.

 

[MILD THUNDER]

Count the splines on the propshafts. 19 spline is a #3, 26 spline is a 3a. My money is on them being #3 drives.

I would keep the gil exhaust, and not put some cheapy manifolds on the engines. You will never hurt a #3 with 420hp mills.

As for the engines, after sitting all these years, I would probably go thru both of them. Good luck, its a cool old boat!

 

[old377guy]

also i was looking to find some replacement exhaust pipes for the port engine, YIKES! i came up with Gil exhaust for what I think I have on there now. Not cheap. Might be easier to sell the riser set i have and find something a bit cheaper for both engines. I have both sets of the manifolds so i should be able to resue them as long as there aren't any cracks that i read about for these.

Yeah, kinda like I was saying; get rid of the expensive starboard muffler tailpipes and replace with matching tailpipes for both sides. Of course keep all four exhaust manifolds. And I should've thought to count the splines when we were over there. I told you that the guys here are a wealth of knowledge; just double check any info coming coming out of the Lone Star state though....

 

[BDC1013]

Count the splines on the propshafts. 19 spline is a #3, 26 spline is a 3a. My money is on them being #3 drives.

I would keep the gil exhaust, and not put some cheapy manifolds on the engines. You will never hurt a #3 with 420hp mills.

As for the engines, after sitting all these years, I would probably go thru both of them. Good luck, its a cool old boat!

Thanks i'll count the splines the next time i go see the boat.

The manifolds may be Gils, I am not sure. The riser tail pipes may be gils but i am not sure either. But to find a matching set of those pipes in the picture above for a decent price might be tough, and to think the person that stole them probably got $10 for scrap stainless. uke:

The one engine that is left I need to see if it will run first. If it does, can't hurt to run it till she blows. Will cost the same to buy a couple new long blocks as it will to have that engine gone through.

 

[MOBILEMERCMAN]

What you do is save up and by a couple 502 partial engines buy intakes and carbs and put your gils on it. While your saving keep an eye out for tail pieces.

 

[Ratickle]

Let me see what I have sitting around for Gils etc. I gave some to others, but they may still have some of it too. I had 420's in the Scorpion before I changed it to the 540's.

If it was much of a saltwater boat, the engines are probably "fall apart's" anyway......

My money is on #3's, not 3a's, too.

 

[Bobcat]

I'm digging this thread !

 

[BDC1013]

What you do is save up and by a couple 502 partial engines buy intakes and carbs and put your gils on it. While your saving keep an eye out for tail pieces.

my goal is to get the boat running for as little money and as soon as possible. I don't know if the place where I am keeping it is going to allow me to stay there for the price they have me at past sept. If it is running, i should be able to find a used hoist to keep the boat on the water at my uncles' place.

I would love a pair of 502's eventually, but this is something i really want to get going for my family, as well as my dad's brother. I would really love to give my respect to my dad by getting the family out on the boat that he loved and once took us out on. I have a few ideas for the boat, like a special name and also we want to scatter his ashes in SF bay.

 

[BDC1013]

Let me see what I have sitting around for Gils etc. I gave some to others, but they may still have some of it too. I had 420's in the Scorpion before I changed it to the 540's.

If it was much of a saltwater boat, the engines are probably "fall apart's" anyway......

My money is on #3's, not 3a's, too.

My money is on 3a's but im usually the first to walk from the table!

Thank you for taking a look to see what you may have.

I know the boat was last run and pulled out in fresh water. It was run in fresh water and only a few times out in SF bay, but always run back through fresh. The boat was from florida so i'm sure it has seen it fair share of salt. We will see.

 

[MILD THUNDER]

Those are definitly gil manifolds and tailpipes. I agree, ditch the muffled style tails you have now, and get some matching standard trs style gil tailpipes.

As for engines, you may be better off finding some nice low freshwater hour takeout engines if you are on a budget. You would also want to replace the oil coolers, and trans coolers, or minimum pressure test them. If they were in salt, they may be toast.

Would be a good idea to pull the drain plugs on the drives. If any water comes out when you first pull the drain plugs, the drives could be rusted and pitted inside. You don't need to completely drain the drives, but just pulling the bottom plug for a second will show if there's water sitting in them. No water, then just POP the plug back in till you get ready to change the lube and use the boat. The ssm III holds about 2.5 gallons per drive I believe. Inspecting and greasing the ujoints, bellows, etc would be a good idea before running it.

Take it slow, one thing at a time. Even if it takes a few years to complete it, you will have a awesome, classic ride when its all done. Try to stay involved with the project though, even when moneys tight. You would be surprised how much you can do/restore with just plain old elbow grease. Even if once or twice a week you get to the boat and clean something, polish something, etc. This way when you do finally get the cash together to purchase some motors, exhaust, and props, the little stuff will be done. Then when it hits the water, it will be a beauty once again!

 

[BDC1013]

Those are definitly gil manifolds and tailpipes. I agree, ditch the muffled style tails you have now, and get some matching standard trs style gil tailpipes.

As for engines, you may be better off finding some nice low freshwater hour takeout engines if you are on a budget. You would also want to replace the oil coolers, and trans coolers, or minimum pressure test them. If they were in salt, they may be toast.

Would be a good idea to pull the drain plugs on the drives. If any water comes out when you first pull the drain plugs, the drives could be rusted and pitted inside. You don't need to completely drain the drives, but just pulling the bottom plug for a second will show if there's water sitting in them. No water, then just POP the plug back in till you get ready to change the lube and use the boat. The ssm III holds about 2.5 gallons per drive I believe. Inspecting and greasing the ujoints, bellows, etc would be a good idea before running it.

Take it slow, one thing at a time. Even if it takes a few years to complete it, you will have a awesome, classic ride when its all done. Try to stay involved with the project though, even when moneys tight. You would be surprised how much you can do/restore with just plain old elbow grease. Even if once or twice a week you get to the boat and clean something, polish something, etc. This way when you do finally get the cash together to purchase some motors, exhaust, and props, the little stuff will be done. Then when it hits the water, it will be a beauty once again!

yep, might be able to get some decent money for these muffled gils, or even do a trade of some sort.

I've been looking for takeouts all over the place. I think finding those is just by luck. I will pull the bottom plug on the drives and see what I get, good suggestion.

Jeff had suggested that i take all of the parts i have and just start cleaning them up and prepping them. I think that is the second step after i find out if this current engine will run or not. If this engine is shot I can get it out of there and tear it down. Clean up all the good stuff and junk the rest. I think taking the drives off it a bit out of my range of room to store this stuff. All the smaller stuff i can clean up wrap and box up.

 

[600sci]

u can tell the differents by the propshaft only, the holes back when, u are correct but not always 100% a must.
the #3 propshaft easy to tell is stepped down and the 3a spline part is as big as the shaft itself !
but counting the splines ofcoarse is also a way !

on your 5K a drive ..well only if in 100% rebuild shape on a 3a
the 3a has #5 gears & shafts, the #3 has the internals from a #4 !
#3 was rated back then for 700 Hp and the #3a for ~800 but they can both take almsot 800-1000 !
a #3 in used condition u can find for 2500-4000 depending on what shape ( drive only ) gimbals go for 1500-2500 each.
exhaust, i would not trusst the old exhaust and buy some stainless marine !

 

[MILD THUNDER]

Yep. The #3 propshaft tapers down right were it comes out of the lower housing. Similar to how a TRS or Bravo propshaft would. The 3A, like he says, has no taper. Just a straight big shaft.

I honestly wouldn't bother even trying to fire that other engine. Even if it does start and run, I wouldn't trust it for long. The seals are more than likely dried up, rings could be rusted, valvesprings weak, etc.

Now, not to say that its junk though. I would remove the engine, and tear it down. If the blocks are not toast from salt, or the heads, then I'd say just rebuild/freshen it. The 420HP Merc was a great engine, and also very easy to duplicate. You can find a older Mark IV 454 block, plenty of those around from hotrodders, old surburbans and pickups, etc. The crankshafts and dimple rods are good GM forged steel units. Also can be found for real cheap. The camshafts were crane, but alot of guys have used the cheaper "sealed Power" replacement cams. They offer some nice cams that are very comparable to the original 420HP crane cam, but about half the cost. The cylinder heads are GM rectangle port heads. These can also be found used/rebuilt for cheap. Same for the intake manifolds. Carb is your basic holley 800CFM double pumper.

What I am getting at, is that sure you can just order some 502 crate engines, probably have around 12-15k in them by the time you dress them with carbs, ignitions, accessories, etc. But I think it would be cool, and cost effective, to restore the boat with the original 454/420HP mills, GIL exhaust, and everything period correct. Granted it might only be a 60mph boat, but....still cool none the less. Now, If you really wanna get silly, you can while rebuilding the engines, build them with the intention of adding a supercharger down the road. Some good headgaskets, dished pistons, better rod bolts and head studs, and a cam ground on a 114LSA. Little things that dont cost that much more. Then once you get her running, a few years down the road, if you feel the need to go fast, you can bolt on some 250/256 blowers, and gain 10+mph!