Mercruiser 470 Hull Front Engine Mount

[Blazeracer]

I looked through the forum and couldn't find and info on what I need to know within the next day or two... First, a touch of history.

Three week ago I knew nothing of boats other than the new Bayliner I had back in 2000 only needed gas. That boat's long gone. I retired from the Army about two years ago then went right back to Baghdad as a contractor. My time is done there and now I live in Dallas TX where the lakes are abundant. So three weeks ago I buy a boat off of Craigslist advertised as "lake ready". It was for about 45 minutes, then the transmission gears in the lower end cut loose. I found another lower end on Craigslist and pulled the bad one off... WHOOSH.. Out comes half a gallon of water from the u-joint bellows. Turns out is has a one inch tear in it.

I'm fairly mechanically compitent so I order a transom seal kit that has all the required parts. While I'm waiting for the parts to arrive I take a peek under the carpet... Well one thing led to another and now the boat has a new glassed in floor, new paint job, new carpet and a new seal kit on the bellows. While doing the new floor I noticed the front motor mount is sagged down almost a full inch. Not being a boat guy three weeks ago I figured that's how it was supposed to be since it was running before. That new lower unit had to be tapped on the last inch. I think most of you here will know what happens next... yeah.. I'll be replacing the coupling this week. As a result of needing to replace the coupling I'll be replacing the head gasket also.

So, here's what I'm wondering before I pull the motor. What is the front motor mount made of and what should I make a new one out of? When I tap on it, it sounds hollow. Is it just glassed in wood? It seems there should be metal plate or something there, but that's car guy in me thinking that. The guy that knew nothing of boats three weeks ago want's to build it correctly. By the way, I have the tool for ensuring the alignment is correct this time, since I now know that the alignment exists...

 

[Bt Doctur]

Re: Mercruiser 470 Hull Front Engine Mount

a block of Poplar fitted to the hull and glassed in place will work.
or some 3 inch microlam.

 

[Don S]

Re: Mercruiser 470 Hull Front Engine Mount

What is the front motor mount made of and what should I make a new one out of?

Those mounts can be made of anything. ALuminum, solid wood or plywood covered in fiberglass, steel. Seen it all.
Your best bet would be to post your question over in the Restoration forum on how to build and glass in the new mount.
This forum is more for engine and drive problems.

 

[Bondo]

Re: Mercruiser 470 Hull Front Engine Mount

Three week ago I knew nothing of boats

Ayuh,... Welcome Aboard,...
I guess I shouldn't mention that the 470s are Mercruiser's redheaded bastard step-child,...
The 1 they Don't support anymore,....

 

[Blazeracer]

Re: Mercruiser 470 Hull Front Engine Mount

I'm gathering that this motor isn't the most desirable one to have now that I own it. However, since I'm in the motor forum, would an automotive Ford 460 work on this motor? One of the biggiest headaches with this beast is the fact the block is aluminum and the head is iron. Swapping the iron head for an aftermarket aluminum head would eliminate the constantly blown head gasket problem and probably come with more horsepower. The cooling system is the sealed type so it never touches sea water. Unless there are some different mounts I don't see why it wouldn't work. From pics I've seen of heads for sale on ebay everything looks identical.

Anyway, all the parts are in so time to pull the motor. I'll be glassing in a block of poplar. Thanks Bt Doctor. Poplar explains why the mount sounds hollow when I tap on it.

 

[jerryjerry05]

Re: Mercruiser 470 Hull Front Engine Mount

Constantly blowing head gaskets??? That is something that motor ISIN"T know for.Start lookin and find the problem.J

 

[bruceb58]

Re: Mercruiser 470 Hull Front Engine Mount

Constantly blowing head gaskets??? That is something that motor ISIN"T know for.Start lookin and find the problem.J

I don't own one but seems like all I read about here regarding the 470s are blown head gaskets...especially if you don't use the Mercruiser one!

 

[guyaverage]

Re: Mercruiser 470 Hull Front Engine Mount

Had my 470 out last spring to change the rear motor mounts and the leaky oil pan gasket, and since the intake and exhaust were already off, I pulled the head and found the head gasket blown in 3 different spots. This was on a 470 that would cruise all day at 4000 rpm and never go over 175-180 degrees, had good compression, great power, and that had none of the typical symptoms of head gasket problems. The deck and head were flat to within .002 and no corrosion anywhere.

Ford 460 aluminum head can be made to work, it will require a hole to be machined for a front water hose fitting. Check out some Ford forums, many people have put the 470 in race cars and other applications, usually you can find some good info there if switching to an aluminum head is something you really want to do. Its not going to be cheap by any means.

 

[zbnutcase]

Re: Mercruiser 470 Hull Front Engine Mount

And if you do an aluminum head I would also use head studs instead of the bolts. If you talk real nice to ARP they might sell you half a 460 stud kit. Don't ask me how I know this....'nutcase

 

[Don S]

Re: Mercruiser 470 Hull Front Engine Mount

The open deck design is the biggest reason for head gasket leaks, but the seldom leak until you over heat. When you overheat, for whatever reason, you loose the head gasket. You can do all you want with head gaskets, aluminum head and whatever. BUT, until you stop the overheat, you will have problems.

 

[45Auto]

Re: Mercruiser 470 Hull Front Engine Mount

Well one thing led to another and now the boat has a new glassed in floor, new paint job, new carpet and a new seal kit on the bellows. While doing the new floor I noticed the front motor mount is sagged down almost a full inch.

Did you check the stringers and transom when you re-did the floor? Sounds like the front motor mount structure is totally rotted out, it's usually tied directly into the stringers ......

 

[Blazeracer]

Re: Mercruiser 470 Hull Front Engine Mount

Thanks for the info guys. I've pretty much learned all the same stuff in the last few days. Non-Mercruiser head gaskets blow everytime, iron head/aluminum block don't play well together when too much heat is involved, and why mine overheated...

When you spin the engine coupling, the prop is no longer turning, nor is the impeller.. which is what happened last time it was in the water as stated in the original post. Once the coupling went it overheated in less than a minute. Luckily we were right by the dock and able to row it in.

Jerry - I haven't constantly blown head gaskets. That's an inherent problem with the 470/485 motors that they are WELL known for. I just blew my frist one.

Guyaverage -Yeah, I've found LOADS of great info on hot rodding the Mercruier 470 motor. Apparently it's the motor of choice for guys who do lake racing at Bonneville in the four cylinder push rod motor class. They ALL run aluminim heads. Most are getting 300hp with a head change and cam regrind naturally aspirated. Tubo apps are pushing over 800hp and are testing the 200mph mark!! This is with our little 470 boat motors...

As far as price aluminum seems like the way to go if you have to replace your head. A single reman iron head will cost $530 plus a lot of shipping. A pair of new aliminum heads from Jegs will run a little over $900 shipped. Add another $100 to get the water hole machined into both heads and sell your second head to another 470 guy and BAM.. All aluminum with more reliability and a 15-20 hp gain for the same price.. but that's for the head only. Add the cost of a taller geared upper unit, four blade prop, four barrel intake from a 485with a quadrajet and it'll start adding up.

Just imagine the look on some dudes face in his $40,000 V8 powered Baja when you blow his doors off then show him your inline four.. haha

 

[Bob_VT]

Re: Mercruiser 470 Hull Front Engine Mount

Okay...... I too am retired AD Army. Thanks you for your service. One of my former co-workers just came back from working in Iraq and when the civilian contractors changed .... they sent him home.

I moved this to the restoration forum.

You probably need to get a goot handle on the structure (or lack of) for the mounting.

The 470 is a beast full of torque. Not in my opinion the best to play with but we deal with what we have. The equal amount of monet invested in a 4.3 V-6 will give you plenty of fun and power. Now is the time when people are unloading many "project boats" and I would suggest watching CL.

 

[45Auto]

Re: Mercruiser 470 Hull Front Engine Mount

Most are getting 300hp with a head change and cam regrind naturally aspirated. Tubo apps are pushing over 800hp and are testing the 200mph mark!! This is with our little 470 boat motors...

Yeah, and I imagine they're turning less than 5000 RPM, they're using the stock Alpha outdrives, and the reliability of their engines and drives is extremely high .......

Big difference between building an engine for a specific racing class where you're only concerned about top speed and about it living for a couple of minutes, and building an engine that'll actually be fun to use in your boat and run reliably for a long time.

Just imagine the look on some dudes face in his $40,000 V8 powered Baja when you

ask him for a tow for the 14th time when your hot-rodded 470 craps out ......

As Bob_VT says, there are a lot of engines out there without the inherent problems of the 470. Unless you're building it for a specific reason to stay within a specific set of rules, there are a lot of cheaper ways to go fast.

Hopefully you're aware of the other issues (heat exchanger, cam seals, charging system, etc) with the 470. This site has a decent write-up on it if you haven't seen it:

http://www.sterndrives.com/470information/470coolantleakrepair.html

 

[NetMatrix]

Re: Mercruiser 470 Hull Front Engine Mount

I to have a Mercruiser 470 for my boat (currently rebuilding motor) I was told by a guy that works at a boat place close to where I live at that is also a HUGE boater. He has a 80's model open floor boat. He said that the best way to solve the over heating problem is get metal ram air induction tubes from like autozone or someplace like that. Mount them so they go directly to the motor no more than 3 inches away from both sides of the motor. He also rebuild the top of the "hood" and put a school on it for better air intake to the motor as well. He's been running the boat like that for I think he said 3 years, and hasn't had any problems with over heating since he did those changes. Now of course that only works while the boat is in motion. Hope this helped somehow or another.

 

[45Auto]

Re: Mercruiser 470 Hull Front Engine Mount

You're wasting your time trying to band-aid 470 overheating problems by air-cooling. If you think that's doing any good at all (it's not) just take the entire "dog house" off from around the engine and run it in open air.

Best thing you can do is make sure that you've got the 4" heat exchanger and not the original 3" one.

 

[Blazeracer]

Re: Mercruiser 470 Hull Front Engine Mount

Yeah, and I imagine they're turning less than 5000 RPM, they're using the stock Alpha outdrives, and the reliability of their engines and drives is extremely high .......

You do realize that lake racing at Bonneville is done in cars, not boats right? There are no outdrives associated with that, but there are Ford 9" rear ends. The 300hp motors run there are very reliable. They get a two mile rolling start, then have to make a 5 mile run at WOT, then turn arnound and back it up with another 5 mile run. Don't forget about the several practice runs that are also made. These are not simple quarter mile runs.

If the cooling system is working as intended on any motor there will be no issues. My VIP is a 1980 with the original motor and I can definitely tell that today was the first time this motor has ever been out. (Scored a cherry picker off of CL yesterday for $150 and put it to use this morning.) I'll tell you what, them Mercruiser mechanics got a racket going on.. From opening the engine cover to motor on the engine stand was less than one hour. That was about 100 times easier than any car motor I've EVER pulled.

The motor work is done and now have to replace that front mount. The guy at Home Depot was nice enough to give me a foot and half long chunk of 4x4 for free yesterday. Initial poking around with a screwdriver indicates there was a block of wood in there that the top inch has disintegrated. Hence the misalignment and subsiquent destruction of the coupling. I can move the innards of the couple by hand. Todays' egenda will be a sawzall and fiberglass kit.

I'll be back on the water on Wednesday if the impeller will pull water out of a barrel and it passes the heat test, which it should. It was working just fine before the coupling went...

Switching to a 4.3 might be cheaper?? So far the total cost for this repair....

Top end gasket kit $79
Coupling off of Ebay - $39 shipped
Cherry picker - $150 which I will recoup from CL when I'm done, so it doesn't count.
Wood block - FREE
Fiberglass kit - $15

Total without cherry picker - $133..

BTW, The boat shop up the street wanted $1,200 for the motor work and to change the coupling. That didn't include fixing the motor mount.

Bob, thanks for your service too... Go Army, beat Navy!!!