V12 crankshaft repair process

That pretty much covers it.

You would never want to grind the crankshaft until you actually had bearings in your hand.

 

Actually you don't want to grind the crank until you had the block align-bored, then install the bearings, and measure the actual ID of the bearings. Then have the crank ground to get the oil clearance exact.
Too many people have the crank ground .010" under just because they have .010" under marked bearings. They end up with too large an oil clearance and low oil pressure.

 

Part of the process.

 

May I make a couple of suggestions, based on a couple of decades of building Italian engines for racing?

1. Get the shaft crack tested first - Magnetic Particle (Magnaflux) - while you are at it, get the rods and big end bolts inspected too, if they are to be re-used. Sometimes, the MPI results can be very bad news.....

2. Get hold of all the dimensional data - sizes and clearances.

3. If possible, find someone who really does know the engine you are working on (and doesn't BS) with any luck he will know a machine shop that knows what they're doing too - all engines have their quirks and "things to watch out for".

4. Read point 2 again - measure everything and write everything down - a spreadsheet is convenient. You may find that the shaft is within new tolerances and only needs a polish - seen that plenty of times. Really good measuring gear and practice in its use is assumed.

5. Dummy assemble and measure all clearances - don't accept anything that is out of spec - check rotation of the shaft in the bearings - already mentioned I know, but a good shaft in a warped block doesn't work....

6. Be really careful about "extra" surface treatments - a lot of it is snake oil...

 

Good advice.

 

A great thread guys. Thanks and keep any extra tid bits coming expecially about the old 4L Lambo engine.

Bob S.

 

Can anyone suggest the best method to clean a crank and prep for reinstall? Granted this is assuming everything measures within spec.

 

I ran an AMC K2000 grinder for many years. I've ground everything from 5hp Kohler cranks to 16 cylinder locomotive cranks, and everything in between. Model A and T cranks were the worst due to being so flexible.

First off, why are you wanting the crank ground? A close inspection should reveal if the crank needs a wheel put to it or not. Did it spin a bearing? is it scored? Bent? Or do you want to "do it right" during a rebuild? Perhaps a polish will get it looking new and keep it in spec.

Once the crankshaft has been found in need of grinding, the next step is to see how much grinding it will need and what bearing sizes are available. If the damage to a journal requires grinding beyond the sizes available, the journal can be welded and brought back to specs by a competent shop.

The sizes are "built in" to the bearing, and a specification is furnished by the bearing manufacturer for a target journal size and a target bore size for the block or rod bore the bearing rests in. This is a realm that not for playing with. Most target shaft and bore sizes have a variance of .001". That means as a machinist, they must be comfortable working in the .0001" range. There is no sneaking up on tolerances of this size. The difference of a human hair (aprox. .0020") can mean a happy engine or one that rips into the shells the first time it's started.

There is a misconception that line boring a block moves the crank centerline significantly. This again rests on the man running the machine. A good machinist will do most of the cutting on the caps, while just barely cutting the block side of the bore. (usually less than two thousandths) The goal is a round properly sized hole.

As stated above, find a competent machine shop that knows your engine and trust in their abilities. Good machine shops are not cheap, so don't let price be the shopping point.

Good luck.

 

A good explanation.

 

Yes,

Nicksons Machine.
FAA Certified..
Santa Maria, CA
(805) 925-2525

Just finished my block,, and are starting on a 1964 Ferrari 330 V12

They are good and fair.
Edwardo

 

Hi T-Man, you obviously know of what you speak! One quick question for you - why would more of the cutting in a line bore occur in the caps rather than the block side? I assume you mean when going up at least one bearing size. Is the goal to re-center (obviously, w/in the limits of the increased bore) so as to cut less of the block side than the cap side in order to preserve as much block material as possible?

Thanks.

 

It was common for the more grizzled builders to ask me to "cut it a little loose" or "bring it to the upper end of the spec". Most times I try to place the spec squarely between the high and low. Periodically someone would bring me a crank I had no specs for and I had to either find bearing specs for it or find out from the customer what was being done with the engine. Quite often with the older engines the block and rods were babbited and had to be bored to fit the crank, so everything started with that.

Many other engines had several different journal sizes along the mains.

If a crank is found to be "tight", it's remeasured to see if it's the journal size, or if the block is over crushing the bearing. If the caps are installed incorrectly, the crank won't turn, either.

As far as regrinding a tight crank, it's very difficult to recenter the crank in the machine with enough accuracy to deal with a thousandth or less, so if more clearance is desired, the machinist usually removes what's needed on the polisher, or will opt to move to the next undersize.

As far as line boring, again, the block is inspected for damage or excessive twist or bow. If it's just a clean up with no spun bearings the caps are removed and shaved a few thousandths where they bolt to the block. This shortens the hole up. Then the block is trued in the machine and the boring bar is set to height. With the caps torqued in place the machinist will begin to cut. If he reaches for a line hone, (stones instead of a cutter) grab your block and run. Line honing is preferred in budget shops for speed and it does a reasonable job, but there is no directional control. Material will be removed from both the caps and block equally, which is what you want to avoid when maintaining the crank centerline is critical.

Here's a boring bar in action. I'd like to see less of a cut on the block side in that video.
http://www.youtube.com/watch?v=aXih7KOKVqY

 

Budget shop? WTF?
Honing is a much more precise method of removing material than boring. Not to mention there is no fractured metal, honing leaves a smoother, more controlled finish.
When fitting aftermarket caps, I bore the caps to within and couple of thousands and finish hone it to size. Otherwise, I cut the caps 2-4 thousands and hone to size.

Ferrari takes it to an even more extreme, main bores are lapped to size.

 

I agree using honing as a finishing step. I've also seen a hone destroy a few engines that drives the oil pump from the nose of the crank. It was honed "just a few thousandths." If the crank centerline must be maintained, you can't beat the boring bar.

 

My experience with 12 cyl engine crank repair is that any required crankshaft resizing on older engines is that acquiring the engine bearings first is important and that on the older engines the .010, .020 uindersizes are the most difficult to find and standard sizes are the most readily available, therefore, I elect to have the shafts hard chromed back to standard.
Cleanness to the point of obsession is imperative, especially the oil galleys in the crank with the blanking plugs removed, my preference is to have the crank ultrasonically cleaned.

I have found that the do it youself person does not normally have the skill nor the measuring equipment to set the crank up properly, therefore my preference is to have the crank sized and fitted to the black by a professional machine shop with impecable credentials, which will require some digging.

Best of luck kdl

 

This is my take on the repair procedures.

Procure al of the bearings including the thrust bearings that you intend to use.
Procure new crankshaft galley plugs.
Gather all of the factory specifications on the bearing seats in the block, including the saddle with for the thrust bearings.
Gather the rod specs for the big end of the connecting rods.
with these specs take/send crankshaft to machine shop, the shop can measure the bearings and with the block specs they can determine the chantshaft size for proper clearance and bearing crush.
The grinding shop would remove the oil galley plugs and hot tank the shaft as well as magnaflux it for crack detection and also check for straightness.
If you would like you can record the before and after data.
It is also very important to take the connecting rods to a god machine shop along with the factory specs for measurement and resizing if necessary. Bear in mind that the rods are
a heavily stressed component.
Have the block checked out for proper bearing bore size, should a line bore be necessary I perfer to use a honing procedure like Sunnedn or Van Norman and not a lathe bit type cutter.
Do not have the machine shop install the oil galley plugs at this time, you may think the crankshaft oil galleys are clean at this time, but you will be amazed at the crud that still remains.
Clean the oil galleys with a long spiral wound steel brush similar to a rifle bore cleaning brush along with some petroleum solvent. Rinse profusly with solvent.
Now send the crank out to a shop specialiging in ultrasonic cleaning of precision parts for aircraft. It will now be clean and ready for the oil galley plugs to be installed.
Use new galley plugs and install them with a little lubricant, I prefer not to use a sealer aor loctite as there is the possibility that some residual amount of uncured sealant will be present in the oil galleys. You may want to peen the alloy plugs just to ensure they are seated properly. At this time check the thred elongation on the main bearing studs or cap screws and replace the nuts if applicable.
With the crank cleaned and the block cleaned you are ready to lay the crank in its bearing halves.
Clean the bearings in solvent and place them in the block, keep the bearings seperated
as pairs and do not mix the upper and lower halves, then smear the bearing shells with assy lube and carefully offer the crankshaft to the bearings and thrust washers.
Take a suitable threaded cap screw about 150 to 300 MM in length and thread it into the rear flange of the crank, this is for leverage to rotate the crank as you proceed.
Rotate the crankshaft befor you install the mian caps to check for smoothness.
Now fit the main caps and lightly torque the caps in the recommended order but not to full torque, rotate the crank again checking for smootheness an binding.
Torque the rod caps to full torque and again rotate the shaft.
The finished job should render a smooth rotation with no slip stick tendencys.

It should be noted that should you elect to have your crankshaft hard chromed, in its future life it will not be possible to magnaflux it. Therefore, you may elect to have it welded up by the submersed welding process---NOT METAL SPRAYED.

THERE ARE MANY SHOPS THAT PERFORM THE HARD CHROME GRINDING PROCEDURES
AND MANY HAVE GONE OUT OF BUSINESS BECAUSE OF ENVIORNMENTAL CONCERNS.
ONE THAT IS HIGHLY RECCOMENDED, BUT I HAVE NOT USED IS (ELECTRONIC CHROME &
GRIND IN SANTA FE SPRINGS, CA ) 562-946-6671

kdl

 

The bearings for these engines are not in the Model T ford era and under no circimstances woul you even consder boring modern bearing. Most modern bearing are tri metal, with the back being steel and the other bearing surfaces are only a tenth or so in thickness, therfore you destroy the intended purpose of a tri metal bearing shell.If all of the macnine work is properly done, each journal will be essentially the same. Plus or minus nothing is unobtainable. The measuring is not for the unskilled. Selecting different size bearing shells is a different matter if they are availablr.

Cheers kdl