dogturd21

Guys, I need some advice. The last time I rebuilt an engine was over 10 years ago- a 454 for a truck...but I recently picked up on a 1998 Merc 454 MPI 385hp- complete engine, EFI, wiring etc. The engine has right at 500 hours and is running fine, but has weak valves in 2 cylinders- leak down testing revealed that.

I want to do this myself, and on a budget- so my plan is to tear it down, and if the pistons are fine then just rering them, new crank / rod bearings, and send out the heads for rebuildng (retangular ports). It will replace a 454 7.4 MPI year 2000 rated at 310 hp.

My question- can I just get one of those hone brushes (with the round abrasive balls on the ends of cables) to hone the cyls ? My concern is that even this will take off too much metal, requiring me to go oversize on forged pistons (another $500 plus). Also, I was looking at Inconel valves and was shocked at the price- about $400-500 for a set of 8 exhaust valves. Should I go with Inconel, or just better SS valves over stock ?Would it be worth putting in $300-400 for some port work ?

The goal is to build a reliable motor. Another option I have is two send this engine out for rebuilding professionaly. I found a souce that can rebuild it for about $2400 (not local to me though), and perhaps cheaper if the current pistons are fine.

Any advice is welcome. I did find a new copy of the HP Books "Rebuilding the Big Block Gen V / VI Engines" to supliment my old 1980's copy of the Rebuild BB Chevy. that was a darn hard book to find, as it is out of print. I had to get this one from the UK.

Shawn D

I am by no means an expert or profesional engine builder, But I put a dozen or so automotive engines together over the years. From what I have gathered, the honing process is one of the most critical and over looked processes (a couple of smart guys told me). I wouldn't use a bead hone (glaze breaker), they will not ensure the hole is round. I would not use a spring loaded stone hone either. Only an adjustable rigid will ensure the hole is round. Which provides better ring seat/seal = more power and reliabilty. Infact the last few engines I had done, we used a torque plate which stesses the block's head bolt holes to simulate an assembled motor, then hone. Suppose to make for a straighter, more rounder hole.

I would guess marine motors have tighter tolerances than auto, since they run a little cooler, the pistons don't grow as much. In either case if the actual clearance is within spec, but just barely, Then I would punch it out. Because it won't be long before it is out of spec. Say if the clearance is .004" +/-.001" and the actual is .0045" - technically it's in spec, but it is 3/4 of the way to being out of spec. It doesn't have as much life as a motor with .0035" clearance. Both are in spec.

Just some intial thoughts.

jayhawk261

A marine engine is not something you want to whip up yourself. There is much more to be concerned with than regular automotive engines. Marine engines run at higher rpm ranges for extended periods of time. this means that a marine engine not only has to make the power, but do so over the long haul. This means different clearances and other items of interest in the build. I have built many hot rod car engines, but I wouldn't dream of telling my boat engine guy how to do it. It is a different world. That being said, find the right engine guy, and have them build what you need with their input.

BadDog

Budget meaning limited funds. If you can scrape the money together let the shop do it and explain your situation. If he has marine motor experience it will likely be cheaper in the long run.

jeff32

I know many car engine builder who tried their recipe in marine application and... long story short, get a marine engine builder...

Otherwise, have a good set of paddle in your boat...at 90% I'm sure what I'm saying is right... You may be in that 10%, I hope you are!

Panther

The piston to wall clearance is actually higher in marine. Sustained rpms under load = hot piston but with a cold engine block.

Shawn D

Putting it that way. That makes sense to me. I realize there are differences between marine and automotive and I don't know them. Are there any differences in Bearing clearance?

Assembling engines has always been a nerve racking kind of enjoyment for me. Not every one has been a success. One small mistake can cost a lot of time and money.

A nick of the crank, a tight bearing, machining chips in an oil galley, a missed dimension, a loose pressed in oil galley plug, Even down to simple stuff like an oil pick too close to the pan can all cause much grief.
But it is cool as heii to fire em up, run the piss out them and have them survive. And then to be able to say you did it.

I can't stress enough to find a great builder / machine shop for the guidance. While I may say I build engines, I really only assemble them. I have all machining (clearance spec'ing), Balancing, bearing blue-printing done by a very competent shop. ( Not all Are)
Assembling an engine prabably only costs $500 to $1000. The last one I quoted was $600. Really not worth it, to take the risks involved, especially if there is a warranty.

If you can have it done with a warranty for $2400, sounds like a deal.

I have a list of assembling tips some where. Things that alot peolpe either forget or just don't do. I'll see if I can't dig it up later. even if you don't do the work, you can ask who ever is if it's worth doing.

bajabob

www.high-performance-engines.com talk to scott miller see what you get for your money you want to spend and i got one year warranty AND THEY SENT MY MOTOR TO MY SHOP FOR FREE

dogturd21

When I found the guy that can do the rebuild for $2400, we specifically talked about marine engines- his quote was about $200 higher than for a similar truck engine, and he went through a number of differences between the two. IIRC, he mentioned extra work on the heads, valve springs, oil pump and bypass valve, marine engine gasket set, and some extra QA stuff as well. I dont have my notes in front of me, but that is what I remember.
The quote was for a stock rebuild, with a 1 year warranty.

http://remanufactured.com/Inboard_Marine_Engines.htm - they seemed quite knowledgable and professional on the phone.

If I did it myself, I would have a local shop do any machine work, but if I can do just the cylinder honing it would save some money. Or I can have the short block prepped and then do the assembly myself. Its just that I would hate to throw out $600 worth of JE Forged pistons if a rering would do the job.

My local shops are starting at $4000 for a long block rebuild.

HaxbySpeed

2400 sounds like a decent price. If you decided to hone it yourself with a ball brush hone like you were saying you probably wouldn't remove enough material to cause clearance issues unless you're already on the loose/worn side. The biggest problem is you'll need to run cast rings if you want to get a good ring seat again with your home honing job. Not really the best option in a boat motor IMO. You can always save your slugs for the next bigger better build!