crank beveling.......in old 4/6cyl Mercs

[mercguy]

some say it works, some say it doesn't? I would think that if O'Brien and Brinkman (both 4cyl masters) did it, then it must be worthwhile? Unstuffs the crankcase? Improves airflow? Let's hear it.................. ;)

[Fast Fred]

I do not know the dudes you have mentioned, litens the assembly which inables
the motor to rev more quickly. the time it takes from when the throtle plates open till the motor reaches max rpm, this time is shorter :cool:

[pops67g]

Crank beveling is a good practice in a mod motor only if all the other bases are covered in doing the build-up. The only stand alone power enhancer in building a mod is probably the ports, but even their effect is seriously limited unless you do everything else you can to wring out the horsepower.

[Mark75H]

I don't think Brinkman recommended it has highly as most other mods; mostly he told how to do it if you thought you needed to.

My opinion of it is that it is copying what Merc started doing on the 66ci 4 cylinder and carried over to the 6 .... to make more clearance for breathing (which became necessary only when they went to the center pinned reeds), but I agree reduced rotating weight could make a motor without a prop rev up faster. Once the prop is in the water the limiting factor is the boat and not the weight of the crank. Balance of the crank and flywheel could affect crank speed changes more then the weight.

Since the crank is hardened steel you pretty much have to do it with a grinder and since it has to be kept round, you have to do it on a lathe. A pretty involved process and very time consuming to do. If you bought the beveled crank that was on eBay a while back .... it might have sold for less than the cost of having a shop modify one.

[Fast Fred]

there is far more to it than just grindin on the crank, there is a relationship between rotating weight and reciprocating, you will find that two hulls with the same power and weight one with a stock assembly and one with a lightened
assembly, the lightened one will consistently nose out the stocker. :cool:

Assembly, not just the crank :cool:

[mercguy]

I don't think Brinkman recommended it has highly as most other mods; mostly he told how to do it if you thought you needed to.

My opinion of it is that it is copying what Merc started doing on the 66ci 4 cylinder and carried over to the 6 .... to make more clearance for breathing (which became necessary only when they went to the center pinned reeds), but I agree reduced rotating weight could make a motor without a prop rev up faster. Once the prop is in the water the limiting factor is the boat and not the weight of the crank. Balance of the crank and flywheel could affect crank speed changes more then the weight.

Since the crank is hardened steel you pretty much have to do it with a grinder and since it has to be kept round, you have to do it on a lathe. A pretty involved process and very time consuming to do. If you bought the beveled crank that was on eBay a while back .... it might have sold for less than the cost of having a shop modify one.

I agree with Sam, grinding on the crank does not do a whole hell of a lot for increasing RPMS, more so doing it to the flywheel and balancing.

[mercguy]

there is far more to it than just grindin on the crank, there is a relationship between rotating weight and reciprocating, you will find that two hulls with the same power and weight one with a stock assembly and one with a lightened
assembly, the lightened one will consistently nose out the stocker. :cool:

Assembly, not just the crank :cool:


I am refering to beveling, which none of these factors (balancing, rotating weight) are behind the idea of it....... :rolleyes:

[mercguy]

there is far more to it than just grindin on the crank, there is a relationship between rotating weight and reciprocating, you will find that two hulls with the same power and weight one with a stock assembly and one with a lightened
assembly, the lightened one will consistently nose out the stocker. :cool:

Assembly, not just the crank :cool:

not necessarily............it depends on the race course.

[mercguy]

Daren,

You've seen pictures of the inside of both my C and my E so you already know my thoughts on this subject. ;)

yep, and we are in agreement David! Just trying to see what others thought about it.........although MONTHS late! ;)

[Fast Fred]

yes, i see,not big on any motor with out a head gasket my self, i do however remeber a old merc the carbs bolted right to the case, no intake to speak of,
on the inside of the case, thare was a stud with a steal reed and a thick reed stop to keep the reed out of the crank. dose that sound like the set up? :cool:

[Mark75H]

Sort of like this, but not exactly. Besides the insiders I've already told, who knows what Merc product this reed cage came out of?

[Mark75H]

Here are images of what Daren is referring to:

[Mark75H]

A std Merc crank used to come with squared counter balance throws like this 6 cylinder:

[Mark75H]

A close up of a beveled crank that only has bevel on the reed side, original size & shape on the bearing side.

[Mark75H]

And this is a stock later 6 cylinder (99ci) crank with some bevel on the counterweights and reeds anchored at the inside

[Fast Fred]

the last crank looks like the one i was thinkin of, a three cyl w/ 2carbs, think it was a 650sumthin,? any way looks like it was done to help it move more air,
seems like alot of them cranks you got are done, must be something to it.:cool:

[Mark75H]

the last crank looks like the one i was thinkin of, a three cyl w/ 2carbs, think it was a 650sumthin,? any way looks like it was done to help it move more air, seems like alot of them cranks you got are done, must be something to it.:cool:

the 2 carb triple is the regular 650

Only the regular crank is mine. All the other pictures came from other people's shops. Two out of maybe a million, not very many.

All Merc 2 7/8 bore motors use the beveled crank and center anchored reeds, 3 cylinder, 4 cylinder and 6

[RichardKCMo]

Sort of like this, but not exactly. Besides the insiders I've already told, who knows what Merc product this reed cage came out of?
Military target drone or chain saw by merc.
RichardKCMo