Merc 420 Cyclone engines

[MOBILEMERCMAN]

Don't let the intake bolts slow you down. Simply grind a box end to fit.

[BDC1013]

Ok I broke the head off the bolt and the damn thing still won't come away from the head. I tried pretty much everything. I don't know why it won't come off. I can get a screwgy between the head and manifold and it just won't break loose.

The intake manifold I haven't even touched. I don't have a 12 point boxed wrench set so I'm going to have to go get one.

I should have been more patient with this bolt, would have been done a long time ago. I headed up using the combination of a cut off wheel and a air hammer to get the head of the bolt off. I've found that under all the paint is powder or metal corrosion from salt I assume?

[MOBILEMERCMAN]

I presume it is one of the long ones. Yes the stainless bolt thru aluminum bonds extremely well with corrosion. The thing is aluminum responds to heat well and expands more then most metals. As the metal cools it draws in the PB blaster. As I said heat PB and patience is the plan. Drilling, tapping, stainless sucks. I have learned it is better to spend time trying everything possible to avoid drilling stainless fasteners.

I suppose my next move would be to drill a parallel hole to the stainless bolt. Something small like 1/8 or smaller. [Just large enough that it wont break] against the stainless bolt in the aluminum. Then repeat the heat spray and patience as you try to work the manifold off the head. The hole should give space to the aluminum, allow PB fluid in deep and release the surface tension the corrosion has built. The air hammer is NOT your friend.

Best of luck.

[old377guy]

Brian, to add to what Jim said about the parallel i/8" hole - lubicrate that bit as you're drilling or you'll snap that bit; not that I've every done anything like that. Good luck.

[Ratickle]

Ahhh, the joys or salt water corrosion.

[BDC1013]

Update:

got the intake manifold off... some signs of water getting down into the valves and also signs of water in the main galley.

[BDC1013]

I still didn't get the exhuast manifold off, but not sure if that really matter right now. I do not have a plan of which route i would like to go on this engine. Ideas?

[Ratickle]

Just peeking at that cam lobe doesn't look real good.


Need the experts in here though...

[MILD THUNDER]

Here is what I suggest. Keep on tearing it all down. All the way to bare blocks. Saltwater, can wreak havoc on the cylinder heads, and blocks.

Once you get them down to the bare blocks, you'll need to take them to a machine shop. Have the blocks tanked, magnufluxed, and sonic tested. When you deal with salt water, the blocks rust from the inside out. What happens here, is that your cylinder walls can get thin. A quality sonic test can mean a block thats good, or a block thats scrap.

Same goes for the heads. You will want them cleaned, and magged for cracks. You need to be careful with heads. The heads you have, while they are a good performing head, can cost a lot of money to redo. If they need valves, seats, welding, etc, the machine shop ticket can add up quickly. Its not uncommon to have 1,000 or more into fully redoing a set of these older heads. Of course alot depends on your budget, and HP goals. If your on a budget, which I believe you are, it may be money well spent to get two sets of Dart 308 Iron Eagle heads. Actually, the Summit Brand 308 Iron head, is made by Dart, and even less money. These heads will outperform the GM Rect ports, and brand new castings in my opinion is always better than rebuilt old castings.

The blocks. What you have there, is somewhat basic, but a good quality setup. The Crankshaft is very good, and so are the Rods. With the Rods, you have two options. #1 is rebuilding the old rods. You'll probably have around 200 per set of rods, possibly a little more if you go with the ARP bolt option for them (which I would for the few extra bucks). Or, you can opt to go with a new set of H beam rods, scat, eagle, etc, which is a better stronger rod, for around 400 per set with the good ARP bolts. Usually you can ebay the stock rods for 75.00-100.00 a set, and in the end, you have brand new stronger rods for a couple extra Hundo.

Pistons are pretty cut and dry. You'll want a quality forged piston. Theres a couple things you need to watch for. If you plan to, or even think down the road, you may want to go with a roller cam with some high lift, you'll need to watch if you use a stock speed pro/GM replacement piston for those engines. Sometimes, piston to valve clearance can be a issue. Theres alot of options for pistons out there for what you have.

Going to a hydraulic roller cam is awesome for power, but pricey. The crane 134561 cam would work nicely, and has a really nice sound in a 454. CRANE 134561 BBC CAMSHAFT HYD; CCH-296-2 $144.79 BUY ONLINE My buddy runs them in his old scarab. Its a bit hotter than the stock cam. With flat tappets, I'd use the Crower 'cam saver' lifters. They have a additional oiling groove, that gives the cam a bit more oil. Helps to prevent wear and lobes going flat.

Of course theres a lots of little things along the way, But I'd say first order of business is tear them down, and get the blocks and heads to a machine shop you trust, and get a clean bill of health on them. Who knows, all might be good, and maybe you'll be able to just polish crank, hone the cylinders, new rings, and start putting them back together. Once you verify your heads and blocks are solid and useable, we can move forward with Parts selection, etc.

[MILD THUNDER]

Just peeking at that cam lobe doesn't look real good.


Need the experts in here though...

I agree. Not even worth messing with it. Flat tappet cams are cheap enough to replace.

My previous post, I may have been gettin a little far ahead of where your at. So, dont get nervous. I'd remove all the rockers and pushrods tonight, and remove the heads. Keep all your valvetrain parts organized and labeled where they come from. Not even so much from a reassemble stand point, but sometimes you find odd things during teardown with a certain cylinder, and its nice to go back and go over the rest of the parts from that cylinder.

With that manifold thats stuck, make up some wooden wedges. Like door stoppers. Try to get a little gap between the manifold and the head, enough to get the wedge started in there. Once its started, get a good sized hammer, and pound away. Try to work it from both sides. Believe me, the wedges work, and dont gall up the parts.

Oh, how did the water passage ports on the intake manifold look ? Any corrosion? Where they meet the head. Those intakes will work nicely for you, they're keepers if they arent corroded up.

[MOBILEMERCMAN]

I'll bet the intake is rotted and the source of the water on the cam. I'll also bet the block has no threads left to secure the heads and the heads are cracked between the seats.

There are many ways to proceed. I have shared my thoughts a bunch. Spend your money on parts { new engine assemblies } not machine labor to test and rebuild 30 year old salt water stuff. It would be a different story if you had both engines and they ran last year.

Sell the stuff off and let someone else waste their money testing, hoping something is any good. The only thing really with any value is the crank and rods to some car guy. None of it will be worth going back in your boat.

[MILD THUNDER]

I do agree with the above post. Salt water, just ruins everything.

He's absolutley right about the headbolt threads in the block. On those engines, the head bolts go into the water jackets. Salt, heck, even fresh water over time eats them up.

Personally, Im leary about buying used engines. Unless they are super low hour freshwater and I know who im buying from. Other than that, its just a gamble. A buddy of mine got burned on a pair of carbed 502 mags last year. Supposedly low hour closed cooling units. What he got instead was this...............only thing useable after spending 9G, was a couple GM cranks, and a pair of carbs. Basically, not even 1000.00 worth of stuff.

[MOBILEMERCMAN]

In the late 80's Dave and I had this expression. New New. We would often laugh. Is it new? New New? Almost new? Yea its got new paint. It is new, it got the aerosol overhaul.

In the 90's I knew a guy that would come by the shop and pull the boxes new parts came in and repacked his junk in it and sell it as new.

At the same time I came to realize after witnessing projects no body ever has the money to do it right the first time but, they always find the money to do it right the second time.

Get it right the first time. Buy new partial engine assemblies. New New in a crate from Merc or GM. Anything else will just be a hard lesson learned before it is all over.

[ROGUE]

All very true and well learned experience I found out all too well. The only reason to tear into those is if you have a desire to learn the hard way on how to rebuild engines which ends up turning into an expensive experience in bad machine shops and poor parts and mistakes. Once in a while you get lucky and manage to keep one alive with little money but for the most part, I totally agree with what MMM said.

[BDC1013]

Yes the last thing i want to do is spend 9K on engines that have wd-40 spray nozzles stuck in the oil pick up. haha that's a shame. I'm looking for some "new new" short blocks. Definitely would like to do a roller cam setup for the extra money i think it is well worth it. Right now I'm still saving up. I like the sound of those dart heads on summit.

At this point i believe Jim is right. I've already ran into some nasty stuff just by removing valve covers and the intake, I think its only going to get worse from here. anybody want to buy an "old old" block? ha

how do you guys feel about the accessories? Coolers, alt, water pumps, ignition, distributors... keep that stuff or sell it? My garage is becoming a quick disaster with stuff from two sets of engines. I've got both transmissions sitting on the floor as well. Maybe i should start thinking about sending out the transmissions to be gone through or checked out? The one that was still hooked up to the "good engine" is probably in good shape, but i bet the other transmission got some water in it from sitting in the bildge all those years.

Im going to be moving the boat again by the end of this month... my affordable storage has run out. Its either going to be in the driveway or at lockheed martin, my friend works there and a 13x40 storage slip is $300 for 6 months. Great deal. Only thing is its outside, and well you cant just walk into lockheed martin if i wanted to do something on the boat.

[MOBILEMERCMAN]

Price partial engines or long blocks. Partials come with everything to hold the oil in. Long blocks need more assembly. Short blocks need heads and all related valve train.

Keep all your accessories, ignition, brackets and the like. All those loose pieces are worth more then you can imagine.

I will say it again. Buy a GM partial. Make the boat work. At some point in the future you want to add more power fine. Do that last.

There will be plenty of surprises along the way. Don't get side tracked worrying about cams and rockers. I wouldn't start sending trannies out yet either. Keep everything together. When you send something out and say I am not in a hurry it will just get set aside, robbed from or lost. Get your engines paid for first.. It doesn't matter how well the trannies work without them.

[BDC1013]

Jim,

10-4 you got it. I have about half of what i "think" ill need to buy partials. Not really sure where to look at prices for these things. Most of the GM stuff in the catalog says specifically "not intended for marine application"

Any ideas on where to go with the old engine as of right now? I'd like to move it asap if i can. What would you list it as? and for how much? I'm not trying to scam anyone... its really probably worth no more than $1000 right? $400 for core and a set of used rods, crank, old heads... $1000?

[MOBILEMERCMAN]

I am chewing on my shoe in my mouth.. The way I am suggesting may not be available anymore. I have a few calls in to see what is still available new new.

[MOBILEMERCMAN]

I found this so far. Still have a few calls in .

They offer 7.4 and two 8.2 's 502. a 450 hp and a 502 hp NEW GM PERFORMANCE MARINE BASE ENGINES. I spoke with the guy briefly he says they come with intakes, dampers, not sure about flywheels. I plan on calling back for more info.

GM MARINE ENGINES(GM MARINE ENGINES)

[BDC1013]

im liking these

425 HP 7.4 liter Part # 74425 $ 6,545
450 HP 8.2 liter Part # 82450G6 $ 7,805
502 HP 8.2 liter Part # 82502RJ $ 12,405

Are these actually GM part numbers? if so... I can order them through work, I can get it at cost. I priced a ZZ502 at work a couple weeks ago with aluminum heads, with intake. it was $9000 shipped to our shop.