Potential Engine Pull Out

John E3

Active Member
Nov 21, 2022
214
Rock Hall, MD
Boat Info
1999 370 Aft Cabin
Engines
Horizon 454
I finally got to firing up the engines for pre-launch check out and was greeted by a hydrolocked cylinder. Apparently the exhaust manifold failed internally and filled a cylinder full to the top. Thankfully it only turned a slight fraction, so I don't think any (more) damage was done.
I was hoping to put off exhaust & riser replacements till next winter due to the extensive amount of other maintenance that was needed. I think 2 owners ago let maint slip, and last owner just used it for a season (no maint AT ALL), and sold it to go back to sailing. So, the time is upon me, now.
Unfortunately it looks like I'm probably not going to get the old manifolds off without drilling bolts. 1 is already missing, 2 snapped, 3 are rusted away and 2 don't have clearance for an impact socket, and probably rusted too much already. This is the "easy" side, too. The outboard side can only be seen with a mirror. The other engine exposed side looks similarly bad. I'm also concerned that the whole engine is well worn. They read 1250 hours, and the heads were done some time ago. They are 7.4 Horizon MPI, 385HP, which is the Gen 6 HO version. With 4 plugs out I can still easily turn the crank with almost sign of compression on the other cylinders. Of course it takes probably a full minute to rotate it 2 turns, but I would expect some resistance. The compression gauge goes over with me on the next visit.
Assuming that I don't find a good result, the next challenge is how to get them out. I searched around here and didn't find an similar arrangements on pulling engines. In the Aft Cabin models (and probably the MY's too) the engines are under the floor of the salon, with pretty decent sized hatches. There appears to be an access panel in the salon ceiling, and a hatch on the helm floor. Might it be as simple as cutting the caulk around the hatch perimeter and lifting it out?
The effort to do this and just pluck them out is probably nothing compared to rusted/snapped bolt fight in the bilge. The marina yard has a setup on their travel lift just for this purpose. I have the tools and experience to drill out bolts, but low confidence I can drill them accurately enough in place, and may not even be possible on the outsides. If they come out, long blocks are going back in otherwise we will be sitting out the season. Paying someone to rebuild them probably doesn't make sense.
 
I would not drill anything out yourself. I would remove the remaining bolts however they come out, snapped or not and then remove the exhaust manifolds. Take the heads off and inspect the cylinders. If the cylinders look ok, I would then give the heads to a machine shop have hem remove the bolts and do a basic valve job. Reinstall the heads and see what you have. Your going to have crap compression because of the exhaust water intrusion and it's probably worse then you think it is.

TBH - your probably looking at long blocks.
 
Removing the bolts is no big deal for me. A little quality time on my Bridgport Mill.
Compression test on inboard cylinders, including the wet one, was quite good, 160-180.
I tried again to remove more bolts with no success. A bolt extractor with an 18" bar and all the pull I could muster just sheared off more of the heads.
I switched to the outboard side, working from the fwd end with one hand was fall more fruitful. 5 bolts out with an 8" socket. 2 are blocked by the plastic elbow, and the aft end is proving difficult to reach. I'm hoping that with the exhaust elbow and riser block off, and the plastic elbow gone, I'll have better access. Once the manifold is off I'll be able to get the compression test on this side. Given the other 4, I'm hopeful to avoid a long block, and removing the hatch.
 
Good luck, sounds like you have a plan.
 
I've ALWAYS found with corroded bolts and nuts that if you try and tighten EVER SO SLIGHTLY first before you try and remove that you break a whole lot less things.
 
I've ALWAYS found with corroded bolts and nuts that if you try and tighten EVER SO SLIGHTLY first before you try and remove that you break a whole lot less things.
If I could get an actual bite on the heads... there just isn't enough hex left on the remaining 5. The difference between the 2 sides is astonishing. One handed pull on an 8" socket wrench was all it took for 5, so far.
 
If anyone needs details on these heads, using the Mercruiser numbers all lead to NLA, based on lots of searching. I was able to locate the GM sheet (attached) for this base motor, 454 Gen 6 HO (original mfg 1990-2000 IIRC) and the head casting number is 12562920. This spec has all the correct buzz words that uniquely identify this motor. I will pull a cover in the next day or 2 and verify if it matches this. They are readily available, NEW, for $1158. A NEW long block is around $8500.
I may go this route to get back up and running faster.
 

Attachments

  • 454ho-crate-long-block-installation-guide-12568774.pdf
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More than likely, you will find the casting number ends with 088
Hmmm, maybe I was mislead in my research. What I found may well be the post GM production version, a new crate motor. I read that when they discontinued making them for production vehicles someone got the rights to continue making them. I did read in several places that they do fit the Gen 6 HO, -only-, not the 'older model' or L29, so they may be compatible.
Thanks for the heads up.
 
2 ways the engine can be swapped from my research. Removing the hatch which really is not that difficult. I had to remove mine to reseal it. Or piece by piece out the door. That seems like a lot more work and not something you would want to do if purchasing a long block.
 
2 ways the engine can be swapped from my research. Removing the hatch which really is not that difficult. I had to remove mine to reseal it. Or piece by piece out the door. That seems like a lot more work and not something you would want to do if purchasing a long block.
Looks like this from the bilge.
20230531_225213.jpg
 
If anyone needs details on these heads, using the Mercruiser numbers all lead to NLA, based on lots of searching. I was able to locate the GM sheet (attached) for this base motor, 454 Gen 6 HO (original mfg 1990-2000 IIRC) and the head casting number is 12562920. This spec has all the correct buzz words that uniquely identify this motor. I will pull a cover in the next day or 2 and verify if it matches this. They are readily available, NEW, for $1158. A NEW long block is around $8500.
I may go this route to get back up and running faster.
Take a look but you will probably find the valve train is non-adjustable. This becomes quite the challenge in head swaps and with surfacing heads. Rather than measuring and having new pushrods made, you might consider aftermarket adjustable rockers if you go the new head route.
Also since you already have the Horizon closed loop cooling, I'd consider moving to a full closed loop cooling system which includes the exhaust risers.
 
Take a look but you will probably find the valve train is non-adjustable. This becomes quite the challenge in head swaps and with surfacing heads. Rather than measuring and having new pushrods made, you might consider aftermarket adjustable rockers if you go the new head route.
Also since you already have the Horizon closed loop cooling, I'd consider moving to a full closed loop cooling system which includes the exhaust risers.
Ah yes this. A whole new concept for me! I've rebuilt a solid lifter engine and a couple Chris Craft 283's with hydraulic.
At this point it's looking more like get the bolts out, inspect and re-install. They were already rebuilt not too long ago. I'm wondering if they reused the manifolds given how bad they are. I got 1 more outboard side bolt out, but the 2 on the port with the hose connection are rusted too bad. I can't drill off the heads back there, but a die grinder with a carbide burr ought to do the trick. Hopefully I can grab the protruding shank and unscrew it. The other 6 offered almost no resistance, but were clean. I'd rather not remove that head if I can avoid it.
The casting number, 14097088, has the 9 with a 2 much more distinct over it. I read it as a 2 since it was so distinct. Came up empty on a search and had to go lookup the correct number to realize what it was. Very odd.
My nephew raised the closed loop point, but the kit is $2500. Hes got an older 370SB and has considered them too. It looks like this would include a bigger heat exchanger to support the extra load, new tstat housing and water pump.
 
As you note, the "full" closed system that includes the headers is larger than the "half" system. Just as a point of order, assuming that was salt water that sat in that cylinder, and was it for the whole off-season? Might be worth putting a camera in all the cylinders before committing to keeping your current long blocks. I always hate to put time and effort into things that may turn out not to be lasting solutions.
 
As you note, the "full" closed system that includes the headers is larger than the "half" system. Just as a point of order, assuming that was salt water that sat in that cylinder, and was it for the whole off-season? Might be worth putting a camera in all the cylinders before committing to keeping your current long blocks. I always hate to put time and effort into things that may turn out not to be lasting solutions.
It was mostly antifreeze. The head is coming off tonight to get the manifold bolts removed, and full inspection. All 4 cylinders on that side measured within about 10psi, 170ish.
 
"Tonight" was a dream as it turns out. I drilled, ground, dremeled and chiseled the heads off the inboard side (5) and ground the 2 on the back side. These 2 were surprisingly easy, and the manifold slipped off and the 2 studs unscrewed by hand. In hindsight I should have used the carbide burr on the exposed ones and skipped killing a set of drills. It made short work on the back 2. Thankfully I was able to get it positioned well. I am -so- glad this boat has a 14ft beam!
The inboard side is a whole other nightmare. After a couple hours pounding and prying (on safe spots) I have managed to get a gap to appear in the mating faces. I think this riser was seeping for years and that caused the bolts to be rusted tight in the manifold holes. The inboard side of the stbd engine looks similarly bad but the outboard sides are significantly better. I suspect that years of being used as a "stepping stone" caused the seepage.
Anyone have suggestions on how to help the manifold slip off the studs? I've been flooding it with multiple rusty bolt products in hope of it seeping down in to the holes and loosening it up. The upper row of bolts seems to be pretty clear, but the lower row is the key hangup. There are only 3 of these at full length the 4th snapped off below the surface of the manifold flange. Hopefully all this banging and wiggling will free up the bolt studs in the head and I can unscrew them and avoid pulling the head.
My father had some "head wedges" that he used on flathead 8's 55 years ago, but they are hiding somewhere now it seems. I was not able to find anything like these online.
Both manifolds were heavily rusted in the exhaust chamber down thru the 3" riser blocks, and on pretty much every inside surface. Water ports were bad, but not as bad as the exhaust area. Lesson learned - drain the manifolds completely rather than leave with antifreeze in them. I don't think I got the antifreeze displacing enough water in some sections. The outboard side seems to have self drained thru the dripless fitting hose.
Are the plastic elbows with drains a reliable fitting? That manifold port was rusted far more than the other 3, and on the outboard side the screws on that port were the ones I couldn't unscrew as the heads were too far gone. Any downside to replacing the drain plugs with drain cocks?
 
Its bad, really bad. Water has pbly been seeping into middle 2 cylinder exhaust ports since installed. This head may be toast.
20230605_190427.jpg
 
After some pondering and consulting with others, a pair of heads seems to be the only logical way forward. Even if the new heads are drop in compatible it just seems wrong to not do both. I should have both off tmrw for a cylinder inspection. Launch day has passed, sigh.
The only good thing going now is stbd looks vastly better, in spite of previous accusations. Outboard side is TBD fully. Gotta get a mirror back there.
 

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