Cross drilled crank ok for 7000 rpms + ?

69 N.O.X. RATT · 11-17-2003, 11:40 PM

I have an opportunity to buy a Bryant crank for a very god deal. A guy had several 4.00 stroke cranks built for a boat, then backed out of the purchase. A good friend of mine works for Bryant and talked him into selling me one for a deal. The concearn I have is that it is a cross drilled crank (for boat use) I have heard this is not the ideal set up for higher rpm use. My buddy is also going to help me build the motor (way more experiance than me) and he says if we run tight bottom end bearing tolerances .0015 or so and restrict the top end of the motor (oil) we will be fine. This is beyond my expertise, any opinions on this.

I have a 6 quart Moroso pan.

[Modified by 69 N.O.X. RATT, 3:41 AM 11/18/2003]

No Go · 11-18-2003, 10:03 PM

Don't have a ton of experience, but .0015 bearing clearance seems awfully tight-I was shooting for .0025.

Also, back in the day I thought it was the IN thing to do...cross drill the crankshaft.

:confused:

69 N.O.X. RATT · 11-19-2003, 01:07 AM

.0015 is tight. Back in the day the thing to do was cross drill the cranks, then they found out at higher rpms the centrificical force of the oil went past the beaings too fast.

Thanks

Anybody else ?

clem zahrobsky · 11-19-2003, 12:40 PM

BBC cranks are crossed drilled and we ran them to 8000 rpm + with no trouble. buy yourself a copy of "chevrolet power",part #24502488 to answer all your questions. .0015 is to tight shoot for .0025/.003.

69 N.O.X. RATT · 11-19-2003, 01:06 PM

Thanks Clem, I will do some research on the clearances.

Ironcross · 11-23-2003, 10:07 PM

A cross drilled crank would be great, but your clearances are too tight for 7000+ RPM`s. Your taking a chance on black bearing the crank.

Quote:

I have an opportunity to buy a Bryant crank for a very god deal. A guy had several 4.00 stroke cranks built for a boat, then backed out of the purchase. A good friend of mine works for Bryant and talked him into selling me one for a deal. The concearn I have is that it is a cross drilled crank (for boat use) I have heard this is not the ideal set up for higher rpm use. My buddy is also going to help me build the motor (way more experiance than me) and he says if we run tight bottom end bearing tolerances .0015 or so and restrict the top end of the motor (oil) we will be fine. This is beyond my expertise, any opinions on this.

I have a 6 quart Moroso pan.

[Modified by 69 N.O.X. RATT, 3:41 AM 11/18/2003]

:thumbs:

norvalwilhelm · 11-24-2003, 03:58 PM

John I thought cross drilling was the way to go and cross drilled my crank years ago. At the speed shop that I worked for we always cross drilled and chamfered the holes. It gives 360 degree oiling.
As far as clearance I always like tight clearances on a big block. I set mine up at .0015 rod bearings and mains after making sure the crank was straight at .002 maximum. I also set piston clearance at .0045. I took it easy at first but after many Nitrous runs tore it down and found the wrist pins starting to seize. No other problems. Went to full floaters after that.
Lunati did a good article on bearing clearances and stated that they are designed for load and temperature to be run at .0025 not .0035 where the load rating goes down and the oil movement goes way up.
I think that at .0025 1 gallon of oil per minute is pumped through the bearing.
I like them tight John and work in a little extra clearance. :) :)

69 N.O.X. RATT · 11-25-2003, 12:27 AM

Thanks Norval. I hope to have this thing together by the first part of the year.
I just bought the ReherMorrison engine assembly books to help out also. I want to learn how to do it right, not just close enough.

norvalwilhelm · 11-26-2003, 04:44 PM

John I thought you were already pretty knowledgable on assembly. While I don't know the latest parts I do check everything, all clearances then check again to prove to yourself everything is right. If you don't understand something go over it and over it until you know how it works. If your gut feeling is that something isn't right it isn't and don't preceed.
Check every valve, every clearance when assembling heads, I mean everything. I don't spot check heads, I test every one. All it takes is one bad assembled vavle.
Good luck John

69 N.O.X. RATT · 11-26-2003, 06:43 PM

Norval,

I can put an engine together pretty well. But I know there are others who are more knowledgable than me.

When I started building long range rifles I quickly found out there are a lot of guys who think they know how to build a quality long range rifle. I did tons of research when I taught at the Marines sniper school and learned a lot about doing it right. I have the same thoughts on building motors. I can do a pretty decent job, but there are lots of guys on this forum who have been there and done that when it comes to motors. I want to be the guy people come to and ask questions about doing it right. I still have a ways to go.

ps, I just got back from a 97 mile ride up and down the coust on the new bike :cool:

norvalwilhelm · 11-26-2003, 09:19 PM

ps, I just got back from a 97 mile ride up and down the coust on the new bike

John that would take Strider and me about 24 hours to cover that many miles. :) :) ]
Glad your enjoying the bike.
John I gave up shooting when I started into horses 18 years ago and I miss it at times. I also shot intercounty precision shooting and combat. Miss then both. I don't hunt anymore. My conscience got the better of me and I don't want to kill anything else if I can help it.
The last thing I remember shooting was a wolf and I regret it still.