300x build using 250xb block

[HST_ONT]

Hi S&F,

Recently picked up a 300x with a one severely damaged cylinder (bottom port side) and windowed block. I'm sure I'll find more carnage as I tear it down.

I also have a 250xb short block that I've been planning to hotrod (300 pm heads, 300 ignition box, 250xb module, etc.). My understanding is that the rotating assembly is the same as the 300x, but the XB block has different port timing which leads to higher compression.

My question is this:

Has anyone ever built a 300x using a 250xb short block, but retaining the 300x heads, reed plate, plenum, ECM, all electronics, etc.?

[Capt.Insane-o]

The x motor is unique to itself in the exhaust chest and a couple other details. The XB is nothing more than what the 300 pm should have been rated at. If the XB/300pm made 275 hp that was on a good day.

[HST_ONT]

Understood - thanks very much for the insight!

Looks like I'll be repairing this block:

[Fonz69]

Just bought a boat with a 2001 300x that lost the same cylinder and windowed the block as well.
can these really be repaired? Or is finding a replacement powerhead a better option?

[PanRonnie]

i wonder if they forgot about the proper torque sequence!?
that would distort cylinder number 6
leave locknuts 9 and 10 at step 2!

[HST_ONT]

Just bought a boat with a 2001 300x that lost the same cylinder and windowed the block as well.
can these really be repaired? Or is finding a replacement powerhead a better option?

Looks all too familiar.

I don't know anyone in my area who does this type of work, and the damage to my cylinder walls (even beyond the sleeve) looks pretty severe. I would love to save the block if possible. I have yet to determine if the crank is salvageable though - this might be step 1...

[HST_ONT]

i wonder if they forgot about the proper torque sequence!?
that would distort cylinder number 6
leave locknuts 9 and 10 at step 2!

Potentially - although I think its more likely it was pitched too high and outside of the proper rev range at WOT. A pair of these came off a 32 skater with a 32P 4 blade BBlades. Its also possible we just happened to lean out the same cylinder. I have yet to flow test the injectors.

[PanRonnie]

Potentially - although I think its more likely it was pitched too high and outside of the proper rev range at WOT. A pair of these came off a 32 skater with a 32P 4 blade BBlades. Its also possible we just happened to lean out the same cylinder. I have yet to flow test the injectors.

you can have some odd results!

[Chaz]

Ronnie is correct on both counts:

The blocks are weak under #6 .. I came up with a fix for that about a decade ago.

I mark all my injectors 1 - 6 .. weak flowing goes on top , heavies @ the bottom.

Lugging down the motors with tight props and marginal octane fuel will also stick a piston .. 5 say go , 1 says no .. as you see , makes a mess. I tried to have rods made that would stop the motor without breaking. No such luck.
I have settled for beams lightly ground , shot peening and cariogenic bath. So far , so good.

Both those blocks can be repaired. Weld up the windows and shrapnel wounds , bore the block .020 , .040 or now .060 over O.D. install new sleeve and bore it back to standard. Touch hone the other five ... and it's ready to go again ..

[HST_ONT]

Ronnie is correct on both counts:

The blocks are weak under #6 .. I came up with a fix for that about a decade ago.

I mark all my injectors 1 - 6 .. weak flowing goes on top , heavies @ the bottom.

Lugging down the motors with tight props and marginal octane fuel will also stick a piston .. 5 say go , 1 says no .. as you see , makes a mess. I tried to have rods made that would stop the motor without breaking. No such luck.
I have settled for beams lightly ground , shot peening and cariogenic bath. So far , so good.

Both those blocks can be repaired. Weld up the windows and shrapnel wounds , bore the block .020 , .040 or now .060 over O.D. install new sleeve and bore it back to standard. Touch hone the other five ... and it's ready to go again ..

Thanks Chaz, and Ronnie!

Can you recommend anyone for the welding/machine work? I'm in Ontario, Canada, but I can ship cross border for the right work to be done.

[FMP]

Try Speedmaster in Schomberg

[MrG]

If you have The window pieces a good welder can put it back you can grind out the sleeve just let the machine shop replace the sleeve seems the engine was over revving that’s what breaks the rods

[Chaz]

Thanks Chaz, and Ronnie!

Can you recommend anyone for the welding/machine work? I'm in Ontario, Canada, but I can ship cross border for the right work to be done.

I would imagine it would be easier and cheaper to keep it inside your own country.

Or use the search feature to find threads and pictures of repaired , high performance upgrades , etc. of 3.0L based engines here on S+F.

No need in keeping the pieces that were spit out in the carnage. If you look at them close you will see that they are "spider web cracked" and will just about break apart in your hands ..

[PanRonnie]

Would it be an idea to have a steel metal sheet part covering the hole from the inside on which you can build your aluminium!?
From my limited experience welding aluminium, it's like building something out of butter!
It's working!, it's working!!!, no it's not!

[Chaz]

It must have been "front half Friday" or something .. LOL



If the area is big enough to require a "back up" I think its better to just tap the spider web out ... grind the hole to a square, rectangle, egg .. out of 3003 or 5052, roll it , chamfer it ... weld it in place .. sand the inside back like it was .. send it again. Better than playin Mr. Dairy-Queen with the puddle ..

(I did whittle a block of carbon as a back-up for a Dart 360 head that shoved a broken valve into the water jacket. Steel, not so much .. the aluminum knows that steel is full of impurities .. and draws out as much black gunk as it can )..





Every block I do seems to have grooves cut by the crank sealing rings. I made a tool that cuts them back to size ..





For a while Merc thought they were OMC and "cold shoved" sleeves into place. You can see the crack (oil spot) in the register .. they came out a lot easier than they went in ..



Broken sleeves (at the bottom) should be bored out. This hole is the split register, 80% slot .. fill , bore oversize install new sleeve ...



Come on 450 , no not porkchop .. degrees