Posted by jdemaris on January 08, 2010 at 08:09:18 from (72.171.0.149):
I think I just had my second bad experience, in a row, with a machine shop. I do most work myself but sometimes try to rely on others that are professionals in machine work. I wonder how many people with less mechanical experience get "lead down the wrong path", or just ripped off, and don't know it?
Got some good input on this forum, thankfully.
I recently posted about my problem trying to figure out what size my main bearings are in a Ferguson TO-35 with the Continental gas Z-134. Rods are all marked .020" under, but no markings on the mains.
I think I figured out what my bearings are. Part of my confusion seems to be some incorrect information I got from a machine shop.
I clamped my two thrust bearing halves together and brought them down to a machine shop. I did that since I don't have a good inside mike, just outside. So, when I measure, I use inside calipers then re-measure with an outside mike.
So, went to the machine shop. The guy laughed a little at me having such a problem that was so "simple." He measured with his inside mike ad told me the bearing ID is 2.24". OK. The standard crank journal is 2.25. He said my bearings are .010" under. I then asked how clearance figures in, and he said his measurements are probably just off by a little. So, I did not feel comfortable with his "expert" measurement since it did not coincide with my bearing shell thickness measurements.
So, after thinking about many comments made here, this is what I did.
I searched through my big engine manual (not the shorter ITT). Found specs. for main bearing bore in the main saddles.
Bearing mount ID is: 2.437" Standard crank journal is: 2.250"
Now, I'm no math whiz, but I figured the following. Space between bearing mount and standard journal is .187". Subtract .002" for clearance and that comes to .185" Then split in half (thickness of each bearing half) and I get .0925" thickness for a standard bearing. Exactly what Earl-IL stated.
I took a ball bearing and miked it at: .311"
I used the ball against the inside of the bearing shell along with a 1" outside mike. Got a measurement of .413".
So, subtract the ball ID from the total and I get .102" bearing shell thickness.
Going by bearing mount ID versus standard journal, and allowing .002" clearance, I come up with these specs for thickness of bearing shells:
So, at this point I am going to assume that my crankshaft is .020 undersize and the machine shop screwed up. So much for hiring "professionals." And, if I find out I'm wrong, well . . at least I don't claim to be a machinist. Just a grease-monkey.
Note that last year, I brought four diesel connecting rods to another local machine shop (we only have two within 50 miles). Engine had no problems; it was just a standard rebuild I was doing. IHB275 with the BD-144 engine. Since it was a diesel, I always get the big ends of the rods checked for roundness and resized if needed. All that entails is shaving the cap a bit, and then reboring to round and proper ID. This is standard procedure for any diesel since high-hour rods tend to get a bit out of round on the big end. I used to do it myself, but no longer have the equipment. So, the shop gave a price of $15 each, and I said OK. A few days later I get a phone call, and the tells me he had bad news. "All the rods are bad." That made no sense to me. Engine had been fine. No spun bearings, just high hour wear. He said he'd closed the caps and was honing and honing until they got so hot he had to stop. He could not get the big-end holes big enough. So, getting very upset, I drove the 30 miles to see for myself. I told him this made NO sense. Well I brought my own mike standards with me. Got there and found out his mike was WAY off. I mean like an 1/8". He then grumbles and said one of his hired guys must of dropped it. I then asked him how often he calibrates his mikes and he got angry with me. So, four rods all now ruined. He said he'd checked around and found me four used rods that would cost me $50 each. I looked at him and replied "cost me?" What are you nuts? I told him flat out that he ruined them with his incompetence and now he wants me to pay? I threatened to take him to court, and he finally agreed to buy me replacement rods - but told me to never come back to his shop.
I'm not trying to bad-mouth good machine shops. I'm sure there are many. But, I have a lot of mechanical experience and still get screwed. So, I have to assume those with less experience get shafted and don't even know it.
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Today's Featured Article - The Nuts and Bolts of Fasteners - Part 2 - by Curtis Von Fange. In our previous article we discussed capscrews, bolts, and nuts along with their relative hardness and thread sizes. In this segment we will finish up on our fasteners and then work with ways to keep them from loosening up in the field. Capscrews, bolts and nuts are not the only means of holding two parts together. When dealing with thinner metals like sheet tin, a long bolt and
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