Crankshaft and connecting rod end play

If you aren't using that Jeep for offroading or other severe duty, I'm pretty sure that amount of crank end play will not be a problem for a long time. Also, you can switch to 20w50 oil for some extra insurance.

My experience is with racing turbocharged Buicks and the spec for the 231 V-6 is .003"-.009". I know of a few of these engines that have survived OK at the 4-500 horsepower level with clearances approaching .020". Once they're over .040" though, you better look out cause the counterweights will contact the main webs. One thing I do after each race season is remove the torque converter dust shield and pry against the flywheel to measure end play w/a dial indicator. Be advised that when the play gets past .015" the wear is accelerated due to shock load. Steve Monroe

I am certainly not an expert in this area, but I just have a question or two. The crankshaft end clearance range you mention are basically 15-65 TEN THOUSANTHs. Is that for the stock engine or with the stroker kit? That would seem small to me as that long crankshaft in the 4 ltr would expand and fill that small gap quickly. Adding a stroker will also increase the amount of heat generated under load, won't it? If that is the case, wouldn't you want your end clearance to be on the high side?

Just curious,

Wayne

The end play in a crank is controlled by a thrust bearing which is usually built into one of the main bearings. Any expansion that would affect end play would be just in the one journal. Some engines don't have thicker thrust bearings available so reducing this clearance would involve welding the thrust surface and machining it back to tolerance. If it were my engine I would run it with the slightly oversize clearances. Steve

I have not attempted a hot vs cold endplay measurement so can't comment much except to say that I think the block will expand more than the crank when hot so the clearance may actually increase a little but that's only conjecture on my part. Steve Monroe

The end play is for the thrust bearing only, the other bearings have greater clearance in them to accomdate differential expansion. And, the thrust bearing only takes a beating is manual transmission (clutch) applications. I would think that in automatic trans installations, the thrust bearing has very light duty. If the truck in question is manual trans. then the life of the thrust bearing is more of a concern.

You also don't have to worry about thermal expansion affecting the clearance, as the two faces of the thrust bearing are somewhere between 1-2 inches apart, not on opposite ends of the crank!

Jon

End play is a little loose. Try changing bearing manufacturers as they don't all have the same clearances. The rods are on the loose side but you didn't say what the overall application was going to be. Racing they might be fine however on a stocker I would go to the tight side. The loose clearance will throw more oil up on the cylinders and increase oil consumption. Also loose engines will knock more. Trust me after you hear your new engine you'll always be listening for that loose clearance so fix it right and never look back. Get it balanced to.

All those clearances are perfectly normal. Neither crank end float nor rod side clearance is particularly vital anyway unless they go way outside specs. In fact the specs are only what that particular engine designer thought best anyway. Look at a similar engine from another manufacturer and the specs will be different for no apparent reason. Your machinist sounds a very sensible chap and is no doubt starting to get well pissed off with you nitpicking every tiny little thing. I've had customers like that and they can rapidly become a royal PITA.

In fact automatic transmissions often are linked to thrust bearing failures in racing use. A weak torque converter can expand (called ballooning) from loading up the engine at power against the footbrake and will take out the thrust bearing or even the crankshaft. Steve Monroe

Umm, yes, forgot about some of the racing abuse people come up with. Like hooking stock transmissions to 15,000 RPM small-block engines.

Yikes!

Jon

"Mike" wrote in message news:...

The side clearances have almost nothing to do with oil throw. It's the clearance between the bearing surface and journal that does it, and this should be minimal. I spent years as foreman in a compressor rebuild shop, rebuilding 17,000 compressors, and found that to minimize oil "pumping," as they call the escape of oil past the rings and into the air system, the bearing clearances had to be at the low end of the range specified by the manufacturer. Too much oil on the walls overwhelms the rings and they end up floating on it instead of scraping it off. We ended up grinding most of the cranks and resizing many of the rods to achieve it. Side clearances, on the other hand, were ignored since they made little difference. A *really* big side clearance might allow the piston to rock a bit, though. Another factor that affects oil consumption is the piston-to-cylinder clearance. The piston gets tossed side-to-side in the cylinder as the engine vibrates, and the lateral motion mixed with the vertical thrust and friction on the rings will lift those rings off the cylinder wall at certain points in the stroke. Many compressors were using aluminum pistons which cooled off and shrank during the unloaded phase (running but not pumping) and would pump a lot of oil. Other that used cast iron pistons were more stable and ran cleaner. I wrote a paper on what I'd found during experiments, and a major manufacturer later changed to cast iron pistons. I don't know if my research had anything to do with it. The side clearances on a main will probably increase with heat, not decrease. The case is usually cast iron, which expands at half the rate of a forged steel crank. The bearing shell is steel, and will probably expand more than the case and perhaps keep the endplay relatively constant. Too small an endplay will result in too little lubrication on the thrust faces. The aircraft engines I now look after have endplays of around .008-.010". Big thrust surface to take the propeller thrust loads, but not all that much bigger than that found in an auto engine.

Dan

I thought about that, but the block is water jacketed (ok, coolant) and the coolant takes away a lot of the heat from the block and dissipates in into the atmosphere. At least, I would think more than the crank. The crank, on the other hand, is in the bottom of the engine where there is no collant circulation and the hot oil from the cylinder walls (that has removed even more heat from the block) is falling on it, and in many cases the crank is turning in the oil reservoir in the pan. It just seemed to me that a long crank in an engine like that would stretch a lot.

I was also curious about the specifications for endplay that went down the the ten thousanths. It just seemd too close of a tolerance, and was wondering if he typed it correctly, like an extra zero.

I'm just trying to learn something here. Thanks,

Wayne

I'm confused over the whole thread. I've ground cranks from airplanes to Cat. cranks and never had anyone bring one back cause there was too much play on the sides. All one can do is clean up the sides and I guess make the bearings fit. You could spray weld all the journals and then grind them as a new crank, but then why have undersized bearings?

The oil is pumped through the crank and can't be worth worrying about a difference in temperature from the water jacket to oil.

So, how is it done ? If you re-grind a crank it will be undersized to what ever (10-20-30-60-90) and the sides of the journals have to be cleaned up thus making them wider.

The only one that I've rebuilt from the ground up was a '54 235 and it ran like a top all over the country. Had to shim the mains with aluminum cans , something about that year you had to make the bearings fit even though they where over sized to the correct dimension. Anyhow, there isn't much you can do about the end plays unless some serious work is done. Something has to be made bigger to get the tolerances as new.

What if you line bored the mains , re-bore the cylinders, and re-grind the crank would it all line up to be those tolerances? I would think not and the extra play would be in your favor, but then I don't know my above question.

Based on at least one other article in this thread, the only length which matters is that of the central main bearing, which is what apparently controls the end-float. That is rather short, and as it is coupled to the block by a constant flow of oil, I would expect them to be at pretty much the same temperature, so I would expect little difference between them. And while one may be forged steel, and the other cast iron, I don't think that there is a sufficient difference in the CTE to worry about it.

If that play is only controlled by the center main bearing, it may well be within reason.

Enjoy, DoN.

When I build my little race engines, we often are fitting custom made cranks to 40 or 50 year old blocks, and getting the end float right is a pain. We go for .005" plus or minus a thou, it's important to have some, too much is bad, but it's never been a critical dimension in the same way as a journal clearance or a pin fit is.

We just look at what we have, pull out the box'o bearings and start measuring. We have been know to lap the bearings on a flat plate with paper, and we have been know to send them out to be surface ground.

On the rod side clearance thing, I have never felt that more was particularly bad, but too little is very bad. I've run up to .050" when the spec was .008" with no bad effect of any kind, including over oiling. Compared to a rod journal clearance of .0015, a side gap of .008" is a huge amount and won't have any effect on oil flow within the engine.

Brian

The side clearances have almost nothing to do with oil throw. It's

I seldom had to touch journal or main fillets or thrust faces unless the crank came from a unit that had run dry, with no oil supply, and even then the damage on thrust surfaces was minimal. Even on compressors that were driven by helical gearing, and had to contend with considerable thrust loads, the faces were fine.

Dan

??? I beg to differ with you. It's obvious when its running on the original center points. I can't see how you could accurately measure the slop without the sides of the journal cleaned up. So leave it all worn out? LOL When it's the last grind of its life you can alter the centers and explain that it has to be balanced or like I loved to do was get it off the machine and throw it and sliding across the floor and into the side of the building. Bang ! It is dead !

Not for the OP

If you saw the readings before the crank was fixed you'd see. Why grind it if the parts aren't worn? The sides or what ever are immune to wear?