1986 3.7 Mercruiser

[Johark53]

Hi everyone my name is joe I'm new to iboats I have a 1988 Wellcraft 19.2 classic with a 3.7 Mercruiser that was given to me the owner bought the boat brand new for his daughter she did something to the motor on the second season. The owner then park the boat in is yard covered for 25 years when I tell you this boat is in factory condition as a professional boat builder would know this I ran a compression test on the motor cylinder 1 2 & 4 had high compression 175 pounds cylinder 3 had 90 pounds so I dropped the oil pan and popped number 3 piston out it appeared to have water in the cylinder the rings were completely seized so I remove the rest of the pistons to replace the rings. My question to you out there that if the motor only has 40 hours on it it appears the motor was overheated telling by the flap in the exhaust was completely melted the cylinders don't look scored should I hone the cylinders .5 and put oversized rings and put new connecting rod bearings? Or should I just clean everything up and put standard size rings and use the same connecting rod bearings or is it even worth fixing. It is a GM block with Ford pistons from a 460 big block with a Ford head 202 valves which are discontinued

 

[Bondo]

It is a GM block with Ford pistons from a 460 big block with a Ford head 202 valves which are discontinued

Ayuh,.... Welcome Aboard,..... It's Mercruiser's Own block, built with Ford parts,....

Merc's redheaded step-child they're tryin' to forget, a problematic motor,....
A Strong 4 cylinder, but with inherent problems,....

Best update available for that package is to pull it, 'n drop in a Chevy 4.3l,.....
The gear ratio works out well,....

Ya just gotta build front motor mounts, 'n find an exhaust y-pipe for the conversion,.....

 

[Scott Danforth]

I agree, why try polishing a turd. pull out the 3.7 liter, drop in a 4.3 liter, save money, go boating

 

[stonyloam]

Sorry guys, I disagree. With the newer 470, and only 40 hours on it it is well worth the rebuild. It is not a GM block, it is a Mercruiser designed block. It uses a Ford 460 head, and 460 pushrods. ALL of the parts you need to rebuild should be available. The main problem with them is that with a aluminum block and an iron head, if you overheated you would blow the head gasket. If you rebuild with a genuine Mercruiser OEM head gasket, and change the impeller in the outdrive at least every other year you should be good for 30 years or so. I would not even THINK about going through all the headaches of a swap when a rebuild will do just fine. IMHO of course!

 

[stonyloam]

OK I have a little more time now. There are three basic problems with the 470 engine. Here they are one at a time:

Charging system: The 470 uses a rotor-stator system like an outboard. The rotor (replacing the harmonic balancer) is lined with magnets and rotates around a stator to creat electric current. This works fine, however the weak point in the system is the water cooled solid state voltage regulator. Eventually the heat generated in the regulator will cause it to fail. The problem is that the regulator is EXPENSIVE to replace, and most folks do an alternator conversion when it happens. With 40 hrs. yours could last many years and is a relatively easy about $300 fix.

Water pump cam seals: The 470 engine water pump uses an impeller that is bolted directly to the end of the camshaft. The pump housing has two seals othe cam. Eventually those seals will fail and coolant will leak. If you replace those seals during the rebuild you should be good for a long time. I did mine 10+ years ago and are holding fine.

Head gasket: yeah, this is the BIG ONE LOL! The 470 has an open deck alominum block, with a iron Ford 460 head. This is fine EXCEPT that the two dissimilar metals expand and contract at different rates when heated, so if you overheat a 470 you will probably have a head gasket failure. That problem can be petty much solved by doing two things: when you rebuild use a OEM Mercruiser head gasket (that has special sealing surfaces molded in) and change your impeller in the outdrive water pump at least every second year (every year would be good). You already have the 4" heat exchanger which helps.

Now for the good stuff: It is at least 100 lb lighter than a V 6. Has good power and economy. It (in spite f what some say) is as reliable as other engines of that vintage. It is antifreeze cooled and winterization is a snap, just one plug removed from the exchanger (5 min job) any you are freeze protected.


The fact that #3 was stil holding 90 sounds like you have a really good core to start with. As far as the cylinder wall, sounds like it might clean up, so I think I would go ahead and clean it up and if there were any question take it to a machine shop and have them measure the cylinder for size and roundness. See what they say. They should be able to get valves if you need one. When I had my valves done I had hardened exhaust valve seats put in. Good luck and welcome (hopefully) to the 470 club.

 

[Scott Danforth]

for the cost of rebuilding a 470, you could buy two running 4.3 liter motors with low hours.

as far as red-headed oddball engines go, there are worse ones out there.

the issue with the 3.7 is the floating bores in the block which contribute to the leaking head gaskets along with the iron head / aluminum block. then there is also the original undersized heat exchanger.....etc. I would put an aluminum 460 head on the motor if I were so inclined to rebuild one to eliminate the two different metal thermal expansion issue, along with o-ringing the block bores and installing a laser cut bore stabilizing brace (like we do on Porsche motors). then again, I have the same desire to work on a 3.7 as I do the vazer.

 

[bruceb58]

Unless you can get the 3.7 going for little cost, I would dump that engine in a heartbeat.

 

[stonyloam]

I guess there is nothing wrong with a V6, just need to find one that is a COMPLETE ( including manifolds and exhaust) marine engine, then you will have to fabricate new front motor mounts and make sure everything fits correctly. If you can do the glass work yourself the cost should not be too bad. Yeah, if your engine were completely trashed, the V6 would be the way to go, but it looks like you should have a pretty easy rebuild here. With the "88" boat you should have a 470 with all of the improvements, larger 4" heat exchanger and aluminum exhaust manifold. Good luck, whatever you decide.

 

[Johark53]

Thank you everyone for your feedback!! I ran this engine for two season and she purred like a kitten until number 3 cylinder started misfiring I'm told the reason why water went into the cylinder is because of low compression the motor ran fine until this happened it never overheated everything is brand new in the outdrive water pump rubber boots and I replace the shift cable it was completely seized after sitting 25 years my charging system works well what if I was to add another cooling tank I think that might help with any cooling problems in the future. The only basic problem I really have with 3.7 they discontinued making 460 Pistons you cannot find them if I rebuild the block it would have to be 30 over with oversize Pistons to me that does not sound practical and the cost for $300 I can replace the Rings connecting rod bearing and OME gaskets. I am a professional boat builder in the Tool and Dye industry 32 years. I may not be the best mechanic I know enough to get by when I tour this block down there were no signs of metal filings anywhere in the oil pan

 

[harleyman1975]

I'm with Stony on this one. Rebuild it and run it until it gives you trouble AND THEN switch to a v-6

 

[stonyloam]

You were just looking in the wrong place: check out e-bay http://www.ebay.com/itm/Mercruiser-...ash=item2812334971:g:fZkAAOSwWTRWw0r7&vxp=mtr I am guessing that it may have been the result of the previous overheat, and sometimes they "just fail". Mine started leaking at #4 and never overheated that I know of, but that was after 20 years or so. You do not need a second heat exchanger, the 4" that you have works just fine. As a matter of fact tha original 3" exchangers worked well, but they did not have a lot of excess cooling capacity and when folks neglected to change the impellers, water flow was reduced and there were overheating problems. It is a little different than in a seawater cooled engine where you have both the engine water pump and impeller moving the water, in the 470 ONLY THE IMPELLER is pushing water through the exchanger. You need to make sure the impeller is in tip top shape to maintain seawater flow through the exchanger.

 

[Scott Danforth]

they sell pistons for ford 460's ever day. check out places like summit racing and jegs. you can get stock bore, +.010, +.020, +.030 all the way up to +.125 forged.

infact you can get a set of 4 seal power pistons for the 3.7 on ebay http://www.ebay.com/itm/like/151323812174?lpid=82&chn=ps&ul_noapp=true

Federal Mogul was the original manufacturer of the pistons and rings, and they still make them today under a variety of brand names. with a lot number on the pistons or rings, I could probably trace them back to the person running the machining center (Dad worked at federal mogul for years)

 

[JerryIrons]

I'm in the 470 club as well, (170), and I like it. It's the only boat I've ever had, (about 5 years or so), so there you go. You'll really like the torque this thing has, and I always get comments about how nice my 86 sounds running. And winterizing these things is as easy as it can be.

That being said, there are things to watch out for like above posters have mentioned, if you do keep it I think mostly you want to make sure it's well maintained and learn to listen and keep an eye on it, because you really don't want to cook these engines. I watch my gauges a lot, have a temp gauge coolant valve, spare fluids in boat etc.

In regards to melted exhaust flaps, I once had my water inlet tube come off the outdrive when going out on lake erie. I could hear the loudness in the engine and within seconds shut it off. That was all it took to melt those exhaust flaps, so I wouldn't just assume the engine was overheated because of that.

 

[Johark53]

I've always been an outboard kind of guy so this is my first inboard experience and I do agree she's a power house and I did take into consideration that those flaps could melt very easily my final conclusion that the Rings could have seized over the 25 years never being used I'm going to put new rings then see what happens if I can't get it to go I'll replace it with a brand new 4.3 the boat is definitely worth it

 

[Johark53]

I've done more research guys General Motors produces all Mercruiser blocks for Generations in 2014 Mac cruises trying to get away from General Motors and produce their own block so my motor is a mongrel Ford GM and MerCruiser rough

 

[Johark53]

No Title

 

[JerryIrons]

Holy cow does that look better

 

[Johark53]

Holy cow does that look better

Thank you lot of hard work I am a professional boat builder and I figured what better than using professional materials if anyone needs any questions about fiberglass epoxy Kevlar carbon fiber gelcoat repair water sanding buffer but all I really need to do is get my 470 up and running