1977 Mercruiser 888 repairs

eroemer

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I am in the process of repairing freeze damage to my '77 Mercruiser 888. I need to replace the cylinder heads and exhaust manifolds.

I was told that "all 888's used 351W heads", however, when I pulled the heads, they are definitely stamped "302". Does this mean my 888 has regular 302 heads, OR were the "special" 351w heads that were made specifically for marine 302's (smaller 7/16" head bolt holes) marked "302" to differentiate them from regular 351w heads with the 1/2" holes?

One of my parts sources is trying to sell me used GT40 heads instead....I have found that there are 2 types--GT40 and GT40P--and there are differences in the spark plug angle. Will the GT40 or GT40P heads work on my '77 888? Will the exhaust ports line up? Will spark plug angle affect the exhaust manifold mounting?

While I have it apart, I am also looking at upgrading to a 4bbl intake manifold/carb. Any advice/thoughts on this?
 

Bondo

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I am in the process of repairing freeze damage to my '77 Mercruiser 888. I need to replace the cylinder heads and exhaust manifolds.

I was told that "all 888's used 351W heads", however, when I pulled the heads, they are definitely stamped "302". Does this mean my 888 has regular 302 heads, OR were the "special" 351w heads that were made specifically for marine 302's (smaller 7/16" head bolt holes) marked "302" to differentiate them from regular 351w heads with the 1/2" holes?

One of my parts sources is trying to sell me used GT40 heads instead....I have found that there are 2 types--GT40 and GT40P--and there are differences in the spark plug angle. Will the GT40 or GT40P heads work on my '77 888? Will the exhaust ports line up? Will spark plug angle affect the exhaust manifold mounting?

While I have it apart, I am also looking at upgrading to a 4bbl intake manifold/carb. Any advice/thoughts on this?

Ayuh,.... Welcome Aboard,.... 302s use 302 heads, 'n the 351s use 351 heads,....

If the GT40 heads have the same spark plug angle as yer heads, you can use 'em,....
Otherwise, ya can't put the spark plugs in, because the exhaust manifold will be in the way,....
It's pretty tight, in the stock configuration,....

You'll see 'bout a 20 hp increase, goin' to a 4bbl. carb, 'n intake,...

Btw,.... How have you ruled out a cracked block,..?
If the heads are cracked, I find it hard to believe the block escaped damage from freezin',.....
 

eroemer

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Haven't found any damage to the block (yet) but all we can go on is visual inspection...

Another thread on this forum [ http://forums.iboats.com/forum/engi...602-mercruiser-888-replace-rebuild-or-repower ] is where I was told that the 302 marine engines (888) used 351 heads..

"The heads on an 888 are actually 351w ford, drilled to fit 302 head studs."

When I asked on another boating forum how to tell if my 302 had 302 or 351 heads, they told me all 888's had 351 heads...

The info about the GT40/GT40P was from an automotive forum, and the angle of the spark plug angle is definitely an issue in automotive applications. I was hoping someone here might have first-hand info about the GT40/GT40P in a marine application (on an 888)
 

Bondo

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Haven't found any damage to the block (yet) but all we can go on is visual inspection...

Ayuh,.... Is the motor In, or outa the boat,..?? How much of it is torn down,..??

I do know, I wouldn't spend a dime on that motor, til the block is air pressure tested,....
That'll find cracks that can't be seen,....

I ain't a big Ford guy, so I ain't sure on the heads,...
 

eroemer

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Motor is in the boat. So far have removed the exhaust manifolds, intake/carb, heads. Unfortunately, we don't have the $$/equipment to pull the motor or to replace the entire engine. Hoping we can get lucky and replacing with a few used parts we can get up and running again...otherwise I am afraid we will have to let it go. Cost of used 302/351/GT40 heads are all about the same so am looking to get the most for my limited funds...
 

Bondo

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Motor is in the boat. So far have removed the exhaust manifolds, intake/carb, heads. Unfortunately, we don't have the $$/equipment to pull the motor or to replace the entire engine. Hoping we can get lucky and replacing with a few used parts we can get up and running again...otherwise I am afraid we will have to let it go. Cost of used 302/351/GT40 heads are all about the same so am looking to get the most for my limited funds...

Ayuh,.... I hate to see ya throwin' money away,..... The Odds are the block is cracked,...

Any chance you could get a couple strips of rubber roofin', or maybe some rubber gasket material from a Hvac shop,..??

Then you could put down a piece across the top of the block, 'n bolt the heads back on, then pressure test the block,....
 

eroemer

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Here is why I am somewhat hopeful--we started up the boat to de-winterize by putting on muffs, connecting a hose, and running out the antifreeze. The engine never got hot and ran fine for about 30 mins, but we noticed the water from the muffs appeared to be going into the bilge. Upon inspection we had two freeze plugs popped. We checked the oil for water contamination, and did not see any. We replaced the freeze plugs and tried again. Engine started and ran fine for about 10 mns. This time we got water coming out of a crack in the end cap of port exhaust manifold. Again we found no water contamination in the oil, and the engine did not get hot. We removed the end cap and welded the crack closed, just so we could test it. Replaced the endcap and started it again. This time the engine died after just a few seconds. We now had water in one cylinder on the starboard side. This gave us hope because water did not get into the cylinder until after the exhaust manifold crack was repaired and at no time did we find evidence of water contamination in the oil.

Would there likely be signs of water contamination in the oil after running for 30 mins if the block was cracked? Does water in the cylinder only after closing the crack in the exhaust manifold indicate the water was getting in at the top (heads or exhaust)? We are not experts, but were thinking this might be cause for hope regarding the block...
 

Bondo

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Would there likely be signs of water contamination in the oil after running for 30 mins if the block was cracked? Does water in the cylinder only after closing the crack in the exhaust manifold indicate the water was getting in at the top (heads or exhaust)? We are not experts, but were thinking this might be cause for hope regarding the block...

Ayuh,.... Don't get me wrong, I hope yer right, but,....

Of the 30 minutes ya run it, most of the time, something was leakin' pretty badly, the core plugs,....
Ya fix 'em, 'n then the manifold leak became obvious, as the water level, 'n pressure rose,....
The water in the cylinder could be another crack in the manifold, or in the head,...

I suspect, as ya plug the holes yer findin', eventually, one of 'em gonna be into the oil,....

I ain't a big Ford guy, so I ain't gonna guess where yer gonna find a block crack,....
but I'm thinkin' yer gonna,....
 

eroemer

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Darn....a cracked block would definitely be more than we can afford to fix....
 

johnzonh

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Jun 11, 2008
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I had that engine a few years back... freeze plugs popped. Inherited the boat from my brother (a Ford Mechanic!) who let it sleep over the winter with water in the engine. sure..couldn't see any cracks with the heads off and manifolds pulled but it lost power easily after heating up and water got in the oil. Didn't bother with it either... age of the engine and the cost to pull / replace the block not worth it. Only thing I can say is that the blocks are cheap and common... good luck whatever you decide to do...
 

haulnazz15

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The 888's might have had 351w heads on them, but there isn't a ton of difference in them either way aside from the head bolt size. You will still want to use the 302 intake manifold. However, there are kits that use washers or sleeves to correct for the bolt size. You don't want GT40P's, the spark plugs wouldn't work with the manifolds. The GT40 heads are popular, but still don't provide a ton of benefit for the type of RPM range we utilize in boats. If you've already gone so far as to get new heads, I don't suppose it hurts any to go ahead and see if the block is cracked by getting it all set up, but I wouldn't hold my breath that the block isn't cracked. You'll know soon enough.

Regarding the 4bbl carb/intake, I like the Edelbrock performer intake and the 600cfm MARINE carb. I run both on my 351W and it works great. You'll need to get a larger flame arrestor as well to go with the bigger carb, and the fuel hard-line won't mate up anymore, so you'll need to have a new one made or use an SS-braded version. There will be a bracket needed for the throttle cable as well, as the old 2BBL bracket spacing is different.
 
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pureinsanity

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Jun 15, 2014
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I tore down 3 of the 888's during different stages of building my 77 Mark Twain. The original engine had 302 heads and flat top pistons. Those heads were junk (cracked pieces) also the block was cracked. The other 2 were 75 year model engines and they had 351w heads with slightly dished pistons. One of those hand a cracked block. But I actually run that engine for a season with the crack before taking it back out of the boat. It was cracked to the outside on the back, I patched it and had no issues with it. The reason I ended up taking it out was the impeller went out and it got hot, blowing the head gaskets. So I rebuilt the spare engine (engine #3) I had and put it in. So far it has been a good engine. Both the other 2 engines were cracked in the same place and that was on the back side behind the bell housing. you can patch it and have good results (as long as it's not a closed cooling system) but you are gambling because it still could be cracked to the inside.
Both sets of the 351w heads had the large 13/16 plugs, making them the early model heads. The 302 heads had the 5/8 plugs. I know the head bolt size is different too. Another thing to look at on your heads is the water jacket where it bolts to the manifold. Is it "L" shaped or just rectangular? The "L" shaped ones are the early 351w heads.
 
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