Did the Machine shop hose me on my Nailhead?

Man what a deal! I have been waiting over two months to get my Nailhead back from the Machine shop and finally have it but the Crank doesn't appear measure out right. He told me the crank was good and only needed polished but when I measure the mains and the crank I have 0.003 to 0.004 clearance! Everything I find shows they should be 0.000 to 0.002. So the question is does it need ground and new bearings? it's a 1965 401

 

Is you total difference .004 ? split that and it gives you .002 clearance all around...what does the plastigage say? ....my 2 cents worth

 

Check your micrometer with a standard and make sure it reads zero. Then re-check the journal diameters.

 

I am using a bore gauge for the mains and a micrometer for the crank, guess I could get some plastigage but using the tools should be closer?

 

The micrometer is right on!

 

If the crank polished up nice, and you are happy with it, just measure the journal and the bore with the bearing in and get a .001 or .002 under bearing depending on what you need

 

Some bore gauges have too much spring pressure and dig into the bearing which will show more bearing clearance. You should also check rod bearing clearance.

 

Have been looking for 0.002 bearings but no luck any idea who handles them for the Nailhead

 

The rod clearance is the same story! I may bring home some Plastigauge tomorrow and check it that way, you are right the bore gauge does dig in some.

 

Yep. Assuming your'e measuring it right .004 is too much clearance. I have never had plastigauge let me down.

 

Try Kanter, or maybe Egge, I like to measure them myself, but I always finish with Plasti gauge as said before I have never had it fail me

 

I have a full set of measurement tools plus my own standards and I still use Plastigage as a sanity check. Plastigage has a bad rep and a lot of guys think it's a joke. I find it to be reasonably accurate for what it is, and very useful.

It's so much easier to correct errors at the initial assembly stage rather than later, and it's cheaper too. When I find measurement concerns, I always try to assume that I'm making the mistake, and try to prove myself wrong before I take it back to the machine shop.

If you're confident in your measurements, take everything back to the machine shop and have them double-check it in front of you. I've had to do that many times. A good shop will stand behind their work and correct it, and turn it around in a timely manner.

 

If you have a bore gauge then you should be able to nail the clearance IF you have a .0001 reading head which breaks each thousandth into tenths.

You can use a .001 gauge head but it is pretty hard to interpret as the dimension from one side of a gauge line to the other is around 3/10's of an inch.

With a bore gauge and a micrometer it really does not matter if the mic is correct as you are using these two tools as a comparator. Have the rod bearings installed in the caps and the caps torqued to specs (with lube!!!). Mike the rod journals, they really should be within a VERY few tenths of each other, and then lock the mic. Set the bore gauge with this mic and bring the needle to zero. Put the bore gauge in the rod in line with the beam and your clearance will be shown on the gauge. As you move toward the rod cap (parting line) the clearance will open up to accommodate the bearing "crush" which holds the bearings in place.

If the crank is toward the factory low specification and the rod housing bore is toward the high the clearance will be big.

This same procedure is applicable to the mains.

If you have any questions as far as housing bore dimensions, crank dimensions, torque specs etc. feel free to contact me, I am glad to help!!!

 

Yep, that needs to be repeated.

Sadly, that bad rep is perpetuated by people that don't know as much about what they're doing as they should. If one knows how to use it and read it, it's very accurate. I can't recall an instance where it disagreed with mechanical method to anything over .0005

 

Get some green plastiguage. A tolerance of .000 is too tight. .0015 to .0025 is better. I'm assumimg some hot rodding with these numbers.

A half thousandth's is a very tiny amount indeed. If your measuring tool is digging into the bearing shell enough that you can see or feel it your measurement probably isn't accurate. The tools SHOULD give more accurate numbers than plastigage but I believe they are intended for use on hard steel surfaces.

An extra half or whole thousandths clearance is far better than a thousandths too little. I once owned an ancient Minneapolis Moline tractor that had around 6 thousandths clearance on a rod bearing. If I kept a load on it and didn't rev it up too much it really didn't sound too bad. However, at a fast idle while stopped in the road for instance it would knock so bad it would make you wince! Used it that way for 2 - 3 years. Still running when I traded it off.

Good luck
Worken2much

 

measure it with the plastigauge, just because thats what the mic says doesnt make it correct.

jeff

 

I prefer the Sealed Power foil strip gauges over plastigage.

Haven't seen them for sale anyplace in years. What I have is 35 years old and still works fine. No guessing with this stuff.

 

The hotter the engine, the looser things should be down there. (to a point, of course) When I have cranks cut for street/strip engines, I always have the machinist take an extra thousandth. At higher RPM, this keeps the journal temp down and compensates for the extra twist and flex that happens when you spin things faster than the factory intended.

 

If you can't find the bearings you need and need to tighten things up a bit you could try talking to guys that do the wetable coatings on piston skirts offically it will add 1/2 thou to a surface total of 1thou on a piston.I did a set of ducati pistons a couple of years ago guy said it had a bit of a rattle due to worn pistons loaded up the skirts with heaps of coating so nearly 2 thou bigger after coating.He hasn't been back.

 

Also helps to handle the expansion from extra heat generated under pressure. Double check the measurements to be sure, if it's a thousandth bigger or so, I wouldn't worry about it. Better to be a hair loose than too tight!

 

Double check with the plastigauge.

I'm not a fan of Kanter's plain white box bearings....

LOL, the Nailhead isn't gonna spin more then 6k tops. Power will most likely fall off about 5300.

 

I'd have no worries with .003-.004 total clearance myself. Better to err on being a CH loose than too tight.

Bob

 

The standard unit of measurement known as the "CH" is .0035 inch. This can vary + or - by .0002, but the average is .0035

 

So is this the correct way to figure bearing clearance? 1/2 of the total clearance? OH man,I.ve had some good running engines with really fucked up clearances if that's true

 

All of this about fancy expensive bearings and such for .001 or .002?
Am I missing something? if its under have them turn the crank. if it polished at standard then it will easily clean up at .010 under. problem solved and common name brand bearing are available.

Scot

 

That would also depend on the color of the CH

 

My studies focused on the mid to lighter shades.

 

Red and black err on the thicker side. Easier to see in the teeth tho..........

 

Zman:
Where can I get the .002 main and rod bearings?

 

Lets see $100 for the grind and $175 for a .010 main set and $65 for the rod set or just $175 and $65 for .002 bearings? Wasn't that good in math in school but looks like a $100 savings to me!!!