251 block 265 crank

[Ajgkirkwood]

I just picked up a 251 block without a crank. My 265 block I know is worn. If I use the 251 block, could I use the crank from the 265?

[Frank Elder]

251 and 265 blocks are the same, I don't know if the bore is the same but the crank and rods from a 265 will work in a 251, changing the stroke to a 265.

Edited February 10, 2019 by Frank Elder

[Ajgkirkwood]

I think the pistons are the same. I'm worried if the crank being bigger to not fit or the piston would be sticking out past the deck?

[55 Fargo]

14 minutes ago, Ajgkirkwood said:

I think the pistons are the same. I'm worried if the crank being bigger to not fit or the piston would be sticking out past the deck?

No and no.

The block is the same. The piston goes 1/4 inch deeper into the hole with a 265 because of its crank and rods. Not because of the block..lol

Edited February 10, 2019 by 55 Fargo

[Ajgkirkwood]

6 minutes ago, 55 Fargo said:

No and no.

The block is the same. The piston goes 1/4 inch deeper into the hole with a 265 because of its crank and rods. Not because of the block..lol

 What was the no and no for? With the crank having a longer stroke, the piston would go deeper correct? But also higher? Would they correct this with a different position with a different pin height?

[kencombs]

Pistons and block are the same.  Rods are different, that's what keeps the pistons from going too far up.

 

Just like the 218/230 swap so many do.

Edited February 10, 2019 by kencombs

[Ajgkirkwood]

Ok so the 265 would have a shorter connecting rod to keep the piston lower

[55 Fargo]

44 minutes ago, Ajgkirkwood said:

 What was the no and no for? With the crank having a longer stroke, the piston would go deeper correct? But also higher? Would they correct this with a different position with a different pin height?

Crank will not push pistons outta hole.

With the 265 rods.( specific length for 265 crank).

Thats 1 no.

Crank fits thats 2 nos.

They fit and work in the 250 block.

Time to move on..

Edited February 10, 2019 by 55 Fargo

[Ajgkirkwood]

Thank you Fargo for confirming

[Matt Wilson]

I'm doing such a conversion right now.  The 265 crank and rods will fit into the 251 block.  Earlier 251 blocks need to have clearances ground into the very bottom of the block, adjacent to where the oil pan attaches.  Later blocks already had these clearances cast into them.  I'm not sure what year separates an "early" block from a "later" block.  My block is a "later" 251 block from a 1963 Dodge Power Wagon.  I don't know what the crank and rods came out of.  I managed to buy them from a salvage yard out of state, and they shipped them to me.

 

All other parts are interchangeable.  Be aware that things like timing chains and gears, and pistons (number of rings) and valves (sodium-cooled vs. ordinary), and thermostat housings, can vary across year models or when crossing over from commercial to industrial engines, but not because of any difference between 251 and 265 engines.  Some or all of these differences can be seen between two 251s.  Using the 251 head on a 265 setup will give a decent bump in compression ratio.  On my setup, the crankshaft rear flange bolts right up to the flywheel from my 230, but I'm not sure if they are all interchangeable like this.  The rear engine bolt pattern is the same across all flathead sixes.  The same water pump will fit, too.

 

Be aware that some blocks have the fuel pump opening near the front and others have it near the rear.  Others may be able to add more about this.

 

Good luck!

[55 Fargo]

Interesting on the fuel pump location. I have never seen a rear mounted fuel pump ever. Something odd or rare for certain applications 

Sodium filled valves have not co.e across these yet either but they certainly were manufactured for heavy duty applications.

Yes a head off a 218 228 or 250 will increase compression. All have to be long block versions though.

Edited February 13, 2019 by 55 Fargo

[Merle Coggins]

Sodium filled valves were used in the truck engines of that size.

[Ajgkirkwood]

Call me crazy but I might go for a lower ci. My 265 block might be left alone in the car till i have a replacement motor. That would mean I'll be tracking down a crankshaft. However I'm thinking of getting a 218 crank for a lower stroke. Try to get closer to a square bore. It would have less stress on the internals I think and should get a bump in rpm limit. I'm planning to add some low boost to the motor to help it breath.

 

When using a 218 head to bump compression,  is it milled out more or the pocket is smaller in width because the piston is a smaller diameter?

[55 Fargo]

Hmm ive owned and driven a 218 cdn engine.

Yes shorter stroke but still undersquare at 3 3/8 bore and 4.0625.

A 265 will have much more torque and HP and it will be noticeably stronger even in stock form.

The head on the 218 long block will have a much smaller CC.

Because you would be using a 218 crank and rods your displacement would be higher than 218 as you now sre st 3 7/16 bore or larger with the 265 block.

That in itself would increase the compression.

You most likely can shave that head to attain an 8 to 1 comp ratio.

How much would do it and be no issues with the valves or head gasket life I do not know..

Edited February 13, 2019 by 55 Fargo

[Ajgkirkwood]

in stock form the 265 would be a more stronger motor. the 2 factors in this would be replacement connecting rods, from what i understand you cant buy nos or new connection rods and crank, but a 218 you can. with me adding low boost (5psi) should help it breath in the higher rpm but also make more power over all. 

 

these are the crazy things that go through my head at night.

 

it just clued into me now that if using a stock head from the 265, that compression ratio on a 265 motor is 7 to 1, with a lower stroke, it could drop to 6.5, so a 218 head would be needed. 

 

i have the head for the 251 but a 218 or 230 would be better to use.

 

i know its a change of subject but i read people using sbc valves in the flathead, i saw the shaft diameters to be the same and the valve head is slightly larger, but they are a decent amount longer?

[Frank Elder]

Sooo..... would a 218 25 inch head on a 265 raise the compression or are all the heads the same ?

[Matt Wilson]

On 2/13/2019 at 11:36 AM, Frank Elder said:

Sooo..... would a 218 25 inch head on a 265 raise the compression or are all the heads the same ?

Compression ratio varied for all engines over the years, but if we take a smaller engine and a larger engine having the same compression ratio as each other, then the larger engine will see a bump in compression when the smaller engine's head is installed onto the larger engine.   For example, if we take a 7:1 218 head (25" engine) and put it on a larger 25" engine that also had a 7:1 ratio with its own head, the result will be a higher compression ratio.  Of course, you also have to take into account any milling of the head that may have been done over the years.

 

I'm using the head off a 251 that came out of an early 60s Power Wagon and putting it on my 265.  The manuals say the stock compression ratio for that 251 in the Power Wagon was 7.2:1.  When I cc'd the combustion chambers and ran the calculations, I came up with 7.2:1 for that 251, so that all made sense (for this reason and others, I believe that engine had never been rebuilt, by the way.)  I then ran the numbers for that head on a 265 and got about 7.75:1.  I don't recall if that included boring the block oversize or not, which would have the effect of raising the compression a bit more.  Of course, now I've since had the head milled just enough to make the gasket surface flat again, which was about 0.015", and I cc'd the chambers again, but have not run the numbers on compression ratio yet.  However, the cc numbers didnt change much (I think they went from around 98cc each before milling to about 94 or 96cc after milling - going by memory), so I expect the increase in compression to be mild, which is what I wanted.  I suspect it'll be about 8:1 now, and I don't want it to be up much higher than that.  I also had the block decked, but I haven't taken the effect of that into account yet.  I doubt it'll be much . 

Edited February 14, 2019 by Matt Wilson

[Frank Elder]

Thank you @Matt Wilson

I would like to ask you one more machine shop question if I may, Have you ever heard of anyone truing up any of the other mating surfaces on a L6 block to make sure the fit is perfect for say fuel pump, thermostat housing, water pump, or intake/exhaust flanges?

[Matt Wilson]

4 hours ago, Frank Elder said:

Thank you @Matt Wilson

I would like to ask you one more machine shop question if I may, Have you ever heard of anyone truing up any of the other mating surfaces on a L6 block to make sure the fit is perfect for say fuel pump, thermostat housing, water pump, or intake/exhaust flanges?

Sometimes people true up the surfaces on the intake and exhaust manifolds themselves.  Not sure about the surfaces on the block where the manifolds mount.  If you did that, it would of course require removal of the studs.

 

The crankshaft main bearing bores/saddles occasionally require line boring to get them all to line up with each other, but that's not a must on every engine.  It just depends on the condition of those bores.

 

I don't know of any other surfaces on the block that are routinely machined (aside from things you probably already know about, such as cylinders, valve seats, etc.).  If a gasket surface, such as the ones you mentioned, is damaged, of course the shop can machine it to correct the issue, assuming it's not too badly damaged.  There is another thread on this site (can't recall which thread), where the gentleman describes having to braze some damage (maybe a crack?) to the thermostat housing mating surface on the top of the head, and his shop machined it nice and flat again.

Edited February 14, 2019 by Matt Wilson