I am helping a friend re-power his boat.
He has a 1997 29' Fountain that had a 502MagMPI...
If he chooses to go with the new generation 496HO rather than a 502, what are the biggest stumbling blocks?
My biggest concern is engine alignment because his boat has a solid/race front engine mount and we can not make adjustments easily.
I have been told that the same bell housing and engine mount will bolt up to the new generation block. Is this true?
Does this also mean the crank centerline is the same?
Will it just bolt right in place?

I would have thought this has been done many times...
Am I wrong???

Shouldn't be an issue at all, unless his front mount plate uses some oddball holes in the block.

The front engine mount is a Gil tubular race mount.
It bolts to the same 3 holes on each side of the block as the standard Merc mounts.
I would hope GM kept the same engine mounting locations...

I think you will find that the engine mounts are the same on the 496 as the 502. However, the 496 engine is a little wider than the 502, if you have thru hull exhaust you might have to make some changes to align with the existing transom holes.

Dail

Pat:
The 502mag pan is shallower in the front. The 496 pan is full depth the entire lenght. The mounts should be checked to verify they will fit under the 496 pan. I believe the 496 pan is about 8 inches deep under the front motor mount area, so this is where he will have to check. The engines have the same crank centerlines and outside dimensions and mount points. Other than the oil pan issues the conversion should be pretty straight forward as long as the new motor has the ECM and wiring harness with it. If the oil pan is an issue, Dooley Oil Pans makes a aftermarket replacement thats pretty pricey. You can also cut and modify the stock pan pretty easily, since it is cast aluminum. Hope this helps.
Ray @ Raylar

The 502 & 496 block bolt pattern is the same. Unfortuneately the 502 mount will not clear the deeper 496 oil pan. The good news is that Gil makes a simular mount that works on the newer engine, as I helped them design it. It will work & clear the "cool-fuel" system as well. Your old Gil mount is probably bolted to the stringers with 3/8" x 4" x 6" angle aluminum. All the old mounting holes will not be able to be used. Start from scratch with new angle & fill all the original stringer holes with wood dowel epoxied in, slightly counter-sunk & covered in one or two layers of glass, ground back flush & re-gelcoated or painted. Hang the engine in place with the new Gil mount installed on the engine & the two rear transom-plate bolt assemblies threaded most of the way down, but not snug. Using the alignment tool in the gimbal, locate where to drill the new stringer holes first & install the new angle material with three new 1/2" bolts each. Use Never-Sieze or Teflon grease or regular grease on the threads to save yourself many, many headaches. Then locate & drill your Gil-Mount holes. I believe the ideal bolt size there is 7/16" x 1 3/4" long hex head cap screws. Always use Lock-nuts & flat washers. After you have finished tightening up the front of the engine, go back & snug-up the two rear bolt assemblies. Hope this helps. Ed

Thanks for the great info guys...
I'm going to recommend Gregg sticks with a 502 base engine.
Stringer work and aligning a new front mount are a little over our heads.
Are there still sources for complete 502MPI bobtails?
Or should he buy a new 502 from 1-800-runsnew then bolt the old accessories on?
Thanks again for the help.

Noooo ... go with the 496

I replaced twin 502's in a Cafe Racer without any problems. Did not have to recut exhaust and used same solid motor mounts.

The suprising thing is the 496's ran MUCH better than the 502's. With the Smartcraft and Guardian systems, you won't believe how much more relaxing your boating will be.

G

Definately go with the 496's...If you can afford them. They are very smooth, as he said...Are more fuel efficient, make more horsepower & are faster than the 502's you are replacing, using the same propellers. Ed