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Topic Review (Newest First)
01-25-2013 09:56 PM
vinniekq2 Igary,thanks for that post. I always assume that all engines get some kind of blue printing.Remembering the basics is important. The machine work needs to be accurate and cranks need to be straight. well chosen parts adds to a better engine.
dont rely on luck,do it right the first time.
01-25-2013 09:47 PM
1Gary Often times these threads ask questions that doesn't completely cover the total work needed.

Look at this analysis.

This engine has already gone through turning the crank once.

Now it needs it again according to his machine shop.

But we are rejecting his machine shop's suggestion the crank needs replacement.

Yet we are accepting the machine shop's inspection of the block.Well atleast that fact it isn't cracked.

Me??. The question I have is if we reject the machine shop's suggestion of a replacement crank,why would we accept that this block doesn't need a line bore now what would be a third time being repaired for bearings??. Rains down heavy on me is WHY??. What is creating all these bearings to be chewed up??. Is his crank bent??. Again before the third time isn't a charm,WHY??.
01-25-2013 07:35 PM
BOBCRMAN@aol.com
Quote:
Originally Posted by cobalt327 View Post
I agree- I'll be by in a minute to haul it to the dump to save you the trouble.

Why is it that no one bats an eye at turning a cast 400 sbc crank down 0.200"(!!!) to fit it into a 350 block, but worry about a LJ steel crank being turned down 0.030"??
Amen.. I say Amen!!
01-25-2013 07:30 PM
KA67_72 Shops offset grind the snot out of cranks but it's probably cheaper to buy new. I paid $160 for a 350 Scat crank from Speedway motors. Jegs, and Summit also carry them. At less than $200 it's a no brainer.

Kevin
01-25-2013 06:42 PM
oldbogie
Quote:
Originally Posted by TN6vols View Post
I recently purchased an Chevy 355 that is in need of a rebuild. I took it to the machine shop to get the block checked to make sure it didn't have any cracks. I also took the crankshaft to get it check out. The guy at the machine shop told me that he doesn't recommend using the crankshaft because the mains have been turned down 30 and the rods were turned down 20. Can I use the crank or is it safer to purchase a new one?
This being a forged crank, the turndown of the journals is in a structural sense not an issue; see your comment "The crank is forged steel. So, it needs to be replaced. Ive been thinking about a 383. Is a cast crank ok for a 383 build? " The forged crank comes with more than enough strength to sustain a lot of journal diameter reduction, in fact it's often done on high RPM race motors to reduce the surface speeds between the journal to bearing insert, especially on the rod.

Not all Chevy forged cranks received surface hardening so if it was originally it's now gone; if it didn't have it there isn't any issue. Depending on year of the crank they were made from slightly different materials 1046 or 1053 steel. The older lower carbon 1046 was nitrided to harden the journal surface to improve wear, the later crankshaft forging was made using harder, higher carbon 1053 steel so these shafts usually weren't nitrided as increased surface hardness wasn't needed to achieve the wear qualities they were looking for in a 100,000 mile engine life. There should be casting/forging numbers on the crank that will lead you to which it is.

A 400 horse power level is pretty easy to attain from a 350 with modern heads and pistons at very moderate RPM (under 6000) so it isn't the problem keeping the rotating parts together that it once was. Today this is done on cast cranks with no ill effect; pieces like SCAT's 9000 series cranks are very good if you decide to go that way. However, I'm more concerned with rods, pistons, balance and harmonic dampers these days. The original GM rods, even pink rods, are getting a lot mileage on them which translates to loosing (actually using up) designed fatigue life; so I lack any enthusiasm for reused or rebuilt rods when there are so many inexpensive high quality 4340 replacements out there. For good power the pistons need to work with the head. These days if you want 400 horses without the trouble long duration cams bring, the answer is the L31 Vortec or similar aftermarket clones. Those combined with the timing of something like a Comp XE268H flat tappet, a 750 CFM carb on an Edlebrock Performer RPM, a set of long tube headers it's easy to build a slightly better than 400 horse engine that doesn't have to turn more than 5600-5800 RPMs to do it. This of course means good piston selection which with the need for tight squish/quench clearance of .040 inch means the use of a D dish piston to keep the squish/quench tight on the far side with an adequate D shape dish under the valve pocket to keep the compression around 9.2 to maybe 9.5 depending on vehicle weight and gearing.

The end game I'm getting to is that if your current crank measures correctly for journal diameters, concentricity, and taper; I put my money in better rods, pistons, balancing, a darn good damper and heads.

Bogie
01-25-2013 06:42 PM
cobalt327
Quote:
Originally Posted by TN6vols View Post
The crank is forged steel. So, it needs to be replaced.
I agree- I'll be by in a minute to haul it to the dump to save you the trouble.

Why is it that no one bats an eye at turning a cast 400 sbc crank down 0.200"(!!!) to fit it into a 350 block, but worry about a LJ steel crank being turned down 0.030"??
01-25-2013 03:43 PM
BOBCRMAN@aol.com
Quote:
Originally Posted by TN6vols View Post
The crank is forged steel. So, it needs to be replaced. Ive been thinking about a 383. Is a cast crank ok for a 383 build?
Why would it need to be replaced??

I just sold a steel .040 rod .030 main crank yesterday..

The guy is building a very hot 355 and was very happy to find a steel crank for a reasonable price..
01-25-2013 08:18 AM
vinniekq2 If you are building the engine yourself?
Find a good machine shop,buy a journal.
If you have the time to hand fit each part(basic blue printing) You will have a very good reliable engine when finished. Find the heads you want to use,doesnt matter as long as the castings are good quality.If you decide to use a stock cast iron head,find a set that will yield no more than 9.2:1 CR.Before you purchase or machine the heads,match the pistons from a catalogue of your choice.Post part numbers and have the math guys help with exact fitting.
This means you need to plan the boring and decking of the block to extract the most power and fuel efficiency as possible.The cam specs will be factored in at that time.
The money you spend will be mostly on block and heads,premium machine work,balance the engine.

easy part now is deciding on the bolt ons you like. carb/manifold/exhaust

If you take the time and set your goals reasonable for power,,,? you can use cast or hyper pistons, a flat tappet hydraulic cam and still get an honest 350 HP
01-25-2013 08:06 AM
TN6vols The 400hp is an arbitrary number. I want one hp per cubic inch. If I fall a little short, ok. The engine will replace the 305 TBI that I have in my truck right now. Just putting in a stock 350 will be a big difference over the 305. I don't want to build a race engine I want something that I can drive around and play with sometimes. It is not a daily driver just a toy. I want the engine to last several years and be dependable. If that means it will take a while to build the engine then that is what I will do. I appreciate the guide on the setup @vinniekq2.
01-25-2013 07:51 AM
vinniekq2 read your other thread.You can use w/e quality parts you want.You can build the best or the cheapest.Its up to you how good your project turns out? If you want 400 horse power then decide how often the engine needs to produce that power,how did you pick 400,how long do you want it to last,,,,,?
01-25-2013 07:33 AM
TN6vols The crank is forged steel. So, it needs to be replaced. Ive been thinking about a 383. Is a cast crank ok for a 383 build?
01-25-2013 07:01 AM
vinniekq2 now is a good time to consider a 369/383? Maybe buy an exchange crank from bobcrman or other reputable shop.Get what you want
01-25-2013 06:51 AM
BOBCRMAN@aol.com Look at the crank from the front end. You will see a "parting line" that runs up the front of the crankpin. If this line is 1/16-1/8" wide. The crank is cast. If the line is 3/8" or wider, the crank is forged steel.

Cast cranks last hundreds of thousands of miles in production engines. Unless you are building a 600 horse engine. Cast is fine.
01-25-2013 06:32 AM
TN6vols Im not sure the type of crank. How do I identify the type? Im not building a race engine. I wanting to build a strong 355. I would like to get 350-400hp out the engine. I dont want to build the engine and a year from now I have to replace the crank. I would rather build it right the first time to be durable. Thanks for the replies.
01-24-2013 07:16 PM
BOBCRMAN@aol.com Absolutely nothing wrong with a crank turned past .020.

I am amazed at all the wives tales. The same guys that spread this stuff will read about small journal or Honda rods on a steel crank in a magazine article and think its the hot setup.. What is the difference?? The crank can be used for any journal size. If it is nitrided so what? Any regrind past .010 will usually remove/compromise the hardness. The crank is still usable if it is grindable.

SBC cranks (large journal) can be ground to any of these available sizes..-.010 .020 .030 .040. .050, .060, then to small journal std. -.010 .020 .030 .040 .060 I have all these sizes in stock most of the time. Plus in performance bearings + - .001-.003 increments are available in many undersizes. Then they can be turned to Honda rod journals std. plus several metric undersizes..Just have to watch where the oil hole ends up.

Many of these combos are used in racing. Several of my customers take a new GM steel crank and have the rods off set ground to small journal size, to gain a bit of stroke and reduce deck height. Same with 400 iron cranks.
Back in the day we did 350 cranks, cast and steel, with off set small journals all the time. TRW even had off the shelf pistons for the combo.
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