Mercruiser 7.4 MPI Valve Job . . .

[tpenfield]

Well, I did my end of season compression tests on the engines today. The port engine seemed to be OK . . . The Starboard engine, not so much :facepalm:

While the compression numbers look OK (not great) I did a cylinder leak test on the starboard engine, since the numbers were a bit lower than the port engine.

Here are my numbers

Starboard Engine:

1 = 125
3 = 124
5 = 118
7 = 117

2 = 124
4 = 128
6 = 127
8 = 128


Port Engine:

1 = 137
3 = 129
5 = 126
7 = 135

2 = 140
4 = 134
6 = 133
8 = 140

Engines are closed cooling system - including exhaust.

So, the cylinder leak test on the starboard engine showed a fair amount of leak on # 5, # 7, #2 , #4, and #6 had 80% leak . . . Seems to be the exhaust valve that is leaking on #6 . . . I did not check the others for source of leak.

The port engine appears to have received a valve job at some point in the past, whereas the starboard engine is probably original (830 hours, 18 years)

Anyway . . . looks like I should do a valve job on the Starboard engine (oh joy) . . . My plan is to try to buy a set of built-up cylinders heads (iron) and do a swap of the heads. Then get the old ones re-done and swap out the port engine in another year or 2.

Couple of questions . . .

These are 'Gen 6' BBC (454) engines. I want to see if I can get off of eBay (or elsewhere) a set of rebuilt heads. I suppose I can get the casting number off of the existing heads. There are all kinds of BBC heads that have been made over the years. Anyone have any good cross-reference resources for compatible heads for the Gen 6 engines? Serial #s for the engines are in my Sig below

Anything else that I should consider, other than get a sailboat :noidea:

 

[alldodge]

Well, I did my end of season compression tests on the engines today. The port engine seemed to be OK . . . The Starboard engine, not so much :facepalm:

While the compression numbers look OK (not great) I did a cylinder leak test on the starboard engine, since the numbers were a bit lower than the port engine.

Here are my numbers

Starboard Engine:

1 = 125
3 = 124
5 = 118
7 = 117

2 = 124
4 = 128
6 = 127
8 = 128


Port Engine:

1 = 137
3 = 129
5 = 126
7 = 135

2 = 140
4 = 134
6 = 133
8 = 140

Engines are closed cooling system - including exhaust.

So, the cylinder leak test on the starboard engine showed a fair amount of leak on # 5, # 7, #2 , #4, and #6 had 80% leak . . . Seems to be the exhaust valve that is leaking on #6 . . . I did not check the others for source of leak.

The port engine appears to have received a valve job at some point in the past, whereas the starboard engine is probably original (830 hours, 18 years)

Anyway . . . looks like I should do a valve job on the Starboard engine (oh joy) . . . My plan is to try to buy a set of built-up cylinders heads (iron) and do a swap of the heads. Then get the old ones re-done and swap out the port engine in another year or 2.

Couple of questions . . .

These are 'Gen 6' BBC (454) engines. I want to see if I can get off of eBay (or elsewhere) a set of rebuilt heads. I suppose I can get the casting number off of the existing heads. There are all kinds of BBC heads that have been made over the years. Anyone have any good cross-reference resources for compatible heads for the Gen 6 engines? Serial #s for the engines are in my Sig below

Anything else that I should consider, other than get a sailboat :noidea:

Howdy, I have one of your type engines sitting in my shop, belongs to a buddy. 454 MPI is a 385HP engine which uses 502 heads giving it the extra ponies, 385 of them

Pretty sure your casting should be the one below as with my buddies 1999 model.
14097088...91-up...rect...OPEN...Gen.V 454/502 HO, 118cc chamber

In 2000 they came out with but do belive they a straight 502, but they should also fit but no listing on chamber size
12562934...00-up...rect...OPEN...Gen.VI 502 Marine

http://www.mortec.com/bbc.htm

Edit: Would also suggest doing the whole engine not just the heads. IMO

 

[tpenfield]

Howdy, I have one of your type engines sitting in my shop, belongs to a buddy. 454 MPI is a 385HP engine which uses 502 heads giving it the extra ponies, 385 of them

Pretty sure your casting should be the one below as with my buddies 1999 model.
14097088...91-up...rect...OPEN...Gen.V 454/502 HO, 118cc chamber

In 2000 they came out with but do belive they a straight 502, but they should also fit but no listing on chamber size
12562934...00-up...rect...OPEN...Gen.VI 502 Marine

http://www.mortec.com/bbc.htm

Edit: Would also suggest doing the whole engine not just the heads. IMO

Thanks, AllDodge - I did get a casting number off of the heads "10114156" , which I believe is an oval port head, not the rectangular . . . 118cc open chamber. The intake manifold is 805233C . . . it seems that the MPI intakes are rectangular port, or maybe they are not all rectangular :noidea: . There are an "A2" and "A6" versions of the same part number.

There are a few reman companies that list a rebuilt head for the '156 casting.

My engines are the LX, not the MAG, so I think the HP is more in the 310-330 range.

My cylinder leak test numbers are:

Starboard:

1= 10%
3= 10%
5= 35%
7= 35%

2= 40%
4= 35%
6= 80%
8= 15%

I tested the #6 cylinder several times and rotated the engine in between test, as I could not quite believe the 80% leak, given that the compression on that cylinder was one of the best on that engine (127 psi).

Port:

1= 2%
3= 30%
5= 30%
7= 8%

2= 8%
4= 15%
6= 30%
8= 5%


So, it looks like I may want to do both engines if time and resources permit. Anyway, I'm starting to search for a set of rebuilt heads.

 

[tpenfield]

I am also wondering if I would have the opportunity to go with the rectangular port heads and get a bit more on the top end? Would have to do both engines to match.

 

[alldodge]

Sorry my mistake though you had the Mag engines. Mortec shows 10114156 casting number as oval port 118cc chambers. Could get a set maybe from a junk yard truck engine maybe. You know it takes less then a day to do a set of heads. Only issue is scheduling them into the shop time. It's never taken me more then a week to get a set back, yours can very.

I am also wondering if I would have the opportunity to go with the rectangular port heads and get a bit more on the top end? Would have to do both engines to match.

You can change to rectangular port heads and other mods such as roller cam, but then you would need your ECM remapped. Could pull plenty of power with simple mods, and more HP with a bit more. I'm thinking the simple would be a roller cam, rectangular cast iron heads, and remap and tune the engine and go. Don't see any reason why you couldn't do one at a time, but would need to baby the new engine until you get the second done. To get the real skinny on what you can do I would call Bob Madara (NY) 585-654-8583 or Eddie Young (TN ) 615-216-7449. I've talked at length to both the guys and they are willing to discuss all possibilities.

 

[tpenfield]

Yea, considering I may want to do both engines, I may keep everything as is so as not to complicate matters. Looks like I can get rebuilt heads for about $450 each. First Mate Marine seems to have them ( their part H-6033) and they are sold through various retailers. There are also a few on eBay, etc.

Probably a local shop would be similar money for a valve and seat grind on the old heads. Then there are the gaskets, head bolts, etc. Looking at $1200 each engine. Not sure if I can do better with a set of salvage yard heads. Those may only be a couple of hundred, but still need all the machining.

 

[alldodge]

Just thought of something else, if you build more HP in your engine and your currently running within range at WOT (4200-4600), you will need to increase pitch in your props. Now if you increase HP and gain top rpm lets say up to 4800 - 5200 you may not.

 

[tpenfield]

Just thought of something else, if you build more HP in your engine and your currently running within range at WOT (4200-4600), you will need to increase pitch in your props. Now if you increase HP and gain top rpm lets say up to 4800 - 5200 you may not.

Yea, kind of gets into a whole cascading set of mods and related costs. Prop sets are $1000 each ( x 2), so I think I'll stay with stock LX MPI as is.

 

[tpenfield]

I'm still curious about the intake manifold versus the cylinder head. Would the intake manifold be rectangular port and the cylinder heads be oval ??? does not sound like a match. I am wondering if the 805233C intake is an oval port, yet I have not seen one as such. :noidea:

 

[alldodge]

Yea, considering I may want to do both engines, I may keep everything as is so as not to complicate matters. Looks like I can get rebuilt heads for about $450 each. First Mate Marine seems to have them ( their part H-6033) and they are sold through various retailers. There are also a few on eBay, etc.

Probably a local shop would be similar money for a valve and seat grind on the old heads. Then there are the gaskets, head bolts, etc. Looking at $1200 each engine. Not sure if I can do better with a set of salvage yard heads. Those may only be a couple of hundred, but still need all the machining.

Doing heads should not cost that much, I'm thinking around the $200 to $250 mark including cleaning and machine work for the set. If your heads are straight and only need valve and seat grinding, and seals, it should be less for both heads. Now if you need new springs (most don't for standard lift cams) this would increase stuff.

Edit: while many have replaced heads bolts, I never have unless I figured the engine went through something I need to worry about them, this includes the last 3204 diesel I rebuilt

 

[alldodge]

I'm still curious about the intake manifold versus the cylinder head. Would the intake manifold be rectangular port and the cylinder heads be oval ??? does not sound like a match. I am wondering if the 805233C intake is an oval port, yet I have not seen one as such. :noidea:

From what I can find the intake is the same intake which is used on both HO and standard engines. This tells me the intake ports are rectangular, but tis is not an issue with matching up to oval port heads, it would be an issue if it was the other way around. Those high rise runners is what increases more torque

 

[tpenfield]

Doing heads should not cost that much, I'm thinking around the $200 to $250 mark including cleaning and machine work for the set. If your heads are straight and only need valve and seat grinding, and seals, it should be less for both heads. Now if you need new springs (most don't for standard lift cams) this would increase stuff.

Edit: while many have replaced heads bolts, I never have unless I figured the engine went through something I need to worry about them, this includes the last 3204 diesel I rebuilt

Thanks AllDodge.

I am re-thinking the approach and related costs. Yes, it looks like if I use the existing heads and do all the dis-assembly and re-assembly work, then I can save some serious money. I am going to be way over budget this year as is with the projects and maintenance that I have planned.

So, just checking online for machining prices, it looks like I could have the valves and the seats ground for about $100 per head. Might be a little more if any of the seats have to be replaced.

Just looking at my compression and leak test numbers, I am thinking that I may have a head gasket issue on the starboard engine between #5 & #7, and perhaps some exhaust manifold gasket ( or exhaust reversion) issues on the port engine, based on the higher leakage in the middle cylinders.

So, having a day or two to think about things, my plan would be at this point to do both engines. Probably will do a cooling system pressure check on both engines before I loosen any bolts, just to see how that checks out. Then I can dis-assemble and inspect the heads, send them off to a local machine shop, and finally put it all back together. I think with this approach, I will be in the $800 range total.

Sounds like fun?

Probably should post a few pictures as I go.

 

[alldodge]

Sounds like a plan but normally the cost of doing a valve job includes disassembly and reassembly of the valves and springs. Might be able to save a bit by doing the job your self don't know haven't tried that way in a long time.

One caution to think about, is I've done heads only on an old engine and it didn't work out very well. Did it a long time ago and wound up with more blow-by. At the time was barely seeing some blow-by, but with renewed heads there was much more. Look for a visible ring groove

 

[tpenfield]

Yea, I know that I could do the lower end as well, but we will have to see how the cylinder walls look when I open things up. These engines have about 830 hours on them. Not looking forward to a more extensive re-build, so I am hoping things will look OK.

 

[Scott Danforth]

Ted, does the $100 a head include the shop supplying the valve seals?

with the heads off, would be a good time to port-match the ports, unshroud the valves and debur and polish the chambers

 

[tpenfield]

Ted, does the $100 a head include the shop supplying the valve seals?

with the heads off, would be a good time to port-match the ports, unshroud the valves and debur and polish the chambers

I don't have any exact pricing as yet, just ball parking from what pricing I can find on the internet. I am thinking that since I got to buy a bunch of new gaskets, I can just get the complete top-end rebuilding kit that has the valve seals. So, I could supply them or just do the assembly myself.

As far as the porting and other stuff . . . :noidea: With twin engines, there is no shortage of power.

I did have one thought . . . On the Starbaord engine, the plugs looked fairly black (carbon) no real deposits, just black. On the port engine, the plugs looked more brown-ish as you would normally expect. I am wondering if I have a 'running rich' situation on the starboard engine and if the cylinders are getting carbon build-up?

I might try a de-carbon treatment if I can find something suitable for MPI engines and see if there is a dramatic difference in the numbers before I 'crack' the engine open.

 

[Volphin]

IMHO, the best way to choose a machine shop is NOT by price. Go visit a few. Or ask some local dealers who they use and if they are happy with their performance.
Two 454 heads completely rebuilt should run around $350-450 including seals- out the door. 100 bucks per head? Scary.

 

[tpenfield]

I have used a shop that is about 25 miles away in the past to do some machining on a previous engine. I may start there and check a few others. Anyone got some recommendations for shops on Cape Cod, MA or the greater Boston area?

 

[alldodge]

Have had a lot of heads done over the years and 125 is normal with a 3 angle seat grind per head, but I'm in KY. A 2 angle grind is sufficient for this application.

 

[tpenfield]

Yea, not every place advertises their pricing, but for the ones that do in my area, looks like $120 per 4 cylinder, 2-valve head is typical. A big variable would be if they merely have to do a re-cut of the seat or have to replace the seats as well. That could easily double the price.

I plan on running a few more test before I crack things open, mostly because you cannot do those tests once you open the engine up and are more relying on visual inspection, etc.

Boat budget is looking pretty sick this year . . . Based on all the projects and regular maintenance that I have lined up.