ok probably dumb question but......

[libram]

Can anyone explain simply why a 4 bolt crank is better than a 2 for any other reason than the increased rigity and strength of 2 additional bolts. Is there any short or longterm performance increase? I know its said to be a nice surprise to find you have the 4 bolt and not the 2 but why.

 

[Omie01]

More often than not: Bragging Rights! Especially when it comes to the Cleveland. The 2 bolt mains are just as beefy as the 4 bolt. If you are going to do a performance build of a 2 bolt just go to studs instead of bolts and you will have all the strength you need!! I have personally NEVER seen a main cap/bolt failure in my life, but I don't build motors everyday either. But I have been a part of many builds, including several of my own. All that said I fell into the bragging rights crowd and snagged myself a 4 bolt for my most recent build. But I have a really nice 2 bolt on the back burner if I need another block. There may be other blocks out there that do benefit from 4 bolt mains, but most Fords do not need them for performance builds.

 

[delawarebill]

it depends on the build.. u go full bore and major hp then the 4 bolt is better. but avg nice build with 300 hp and u'll be fine.

 

[Stanglover]

All Cleveland blocks can be turned into 4 bolt mains. The casting already has the bosses cast in, just need to be set up and drilled. A competent machine shop with a big enough radial drilling machine could do it. You just need to find the 4 bolt caps. Even then, I have been told that it is not necessary to do the front and back end caps as there isn't enough material for the extra bolts. Don't quote me on that though.

My theory on why 73's are all 4 bolt mains is simply this; Ford had cast way too many 4 bolt caps (for 71-72 high performance engines) and rather than scrap them, it would be cheaper to add the extra op and drill and tap the blocks. The set up was already in place anyway.

An engine builder friend who builds stock car racing engines (for "mud puddle" racers I call them) has shown me that on Chevy blocks, the outboard bolts are on an angle, which undoubtedly increases the clamping force of the caps on the block. Cleveland's are straight in and are only I think 7/16" bolts. I'm told that these do add strength, but mainly there to stop harmonics between the cap and block. Again, I'm NOT the expert here, but this does make sense to me.

 

[SVO2SCJ]

it depends on the build.. u go full bore and major hp then the 4 bolt is better. but avg nice build with 300 hp and u'll be fine.

I wish everyone (on Facebook groups) would start their questions with your TITLE!    Not a dumb question as you just may not have researched WHY it is done, or WHY say the "value of a Boss 351" is effected!

When a motor is designed it maybe designed for a specific job, weight use/torque ability.  Usually motors that don't see stresses , say of sustained RPM, forced induction or high compression maybe be just fine with both 2 bolt and stock production components.

When "cap walk" was evident after forensic teardown - use of 4 bolt and even "Cross Bolt" (read FE) was designed into the motors.  But it seems to be PERFORMANCE MOTORS.  If a "master builder chimes in .......or let me talk to some Ford engineers at lunch today MY GUESS is it is high compression ratios that warrant the use of special caps AGAIN in sustained higher RPM use.

NOW KNOWING that Jack never used the 4 bolt block or even the Boss crank when building the early 70's Pro Stock 351's ....some with say "well those were high compression"!  1) those motors were almost treated like Top Fuel motors getting torn down weekly.  2) Jack Roush was smart (not cheap) as when he didn't see a issue using 4MA or D0 rods he didn't spend the difference in price (not much in 1971 less than $10 when it came to cranks)

VALUE for the 1971 R code owner - is to own either the original DOAE-L 4 bolt block, a date coded correct for car DOAE-L 4 bolt block or you better have paper work as for a warranty replacement if you have a D1 service or worse a D2AE-CA.  Of course, in the case of the Boss it goes much much farther into "what the factory did" than just the use of 4 bolt mains.   Not having correct block is least of your problems -if you don't have crank, rod, pistons,balancer, flywheel  ALL SPECIAL to the Boss.  (and that is just the bottom end) 

Mark

 

[Stanglover]

I have a book, - The Essential Source Book- Ford Cleveland 335-series v8 engine, 1970 to 1982 by Des Hammill. In it the author describe the reason for 4 bolt caps. So, paraphrasing, when an engine is turned above 6000 rpm, an amount of "fretting" is unavoidable. Fretting is the deterioration of the surfaces of the block and caps due to micro movement of the caps against the block mating surface. So in a nut shell, the extra bolts are thought to stop this fretting between the surfaces. As a former machinist, that makes sense to me. Another "trick" was to dimple the edges of the block to take up any additional play between the cap and block, making the cap a tighter fit.

What was not mentioned previously, is the absolute need for the caps and block to be line bored/honed before assembly.

 

[DK73]

As I see it. Depends on what the engine should be built for. Race or just daily driver. Some time's I feel that I maybe went to fare with my own engine.! My Cleveland is so fast in the traffic. But it is so incredibly [emoji6] But as I look around me. My friends are beginning to go back to original engine. But then have one only for races setup. We know that only the originals are getting sold. Whit the highest price. So if I should change it again. Then I would go back to original horsepower. But it is a big Car. So my 469.5 HK to the flye wheel is what is perfect. [emoji6][emoji106]

Sendt fra min F8331 med Tapatalk

 

[SVO2SCJ]

HI

Spoke to guys (Dominic and Roger) about "cap walk" (Fretting) today. Seemed this first was an issue with the FE race motors in the early 60's - CROSS BOLTS /4 bolt mains were the fix. As for the Cleveland Dominic said I would be suprised if it was more "chest bumping" and marketing AS memos for late 68 from MR Frey were all about performance and CHECKMATTING everything Mopar and Chevy did. And later added that casting caught up with them and there was use in all lines (read Torino/Cougar) WHICH we all know having seen MAY 4 bolt D2AE-CA blocks all the way into 1974!

Mark

 

[rotorr22]

HI

Spoke to guys (Dominic and Roger) about "cap walk" (Fretting) today.  Seemed this first was an issue with the FE race motors in the early 60's - CROSS BOLTS /4 bolt mains were the fix.  As for the Cleveland Dominic said I would be suprised if it was more "chest bumping" and marketing AS memos for late 68 from MR Frey were all about performance and CHECKMATTING everything Mopar and Chevy did.   And later added that casting caught up with them and there was use in all lines (read Torino/Cougar) WHICH we all know having seen MAY 4 bolt D2AE-CA blocks all the way into 1974!

Mark

It was a big issue on the SOHC 427 that was being drag raced on fuel in the 60's. I cannot envision a street type application ever needing them. Now, start playing with power adders (nitrous, turbo's, blowers etc.) and add a bad tune to the mix, cap walk can raise its ugly head. Keep the engine out of detonation, install main cap studs and cap walk should never be an issue. I have seen one engine that had severe main cap fretting and that particular engine also lost all of the bearing crush and had cracked pistons. All resulting from detonation. 

That's why it is advantageous to have your car professionally tuned on a chassis dyno or buy a wide band O2 sensor and do it yourself if you have a street engine set on kill. The state of tune can mean life or death to any high performance engine.

As for the Cleveland, Ford would have been much better served controlling their casting quality and given us thicker and more uniform cylinder walls vs. adding 4 bolt mains. That was the weak point of the factory Cleveland blocks in racing applications back in the day.