Machine shop errors ?? Earl IL et. al. thanks for help

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:

.010" undersize - .0975" thick
.020" undersize - .1025" thick
.030" undersize - .1075" thick
.040" undersize - .1175" thick

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.

jd
there is so much cheap surplus machinery around nowadays any body can be a machinist. al

Another thing you need to watch when having the large end of the connecting rod refinished, is that they maintain correct center to center specs from big end to small end. If they shorten that distance by even .010 during the operation you will have a harder starting engine. I am in the process with dealing with that issue right now as I "screwed" up and did not check piston height over block on an engine.My customer used a different machine shop than I normally use. Another thing, lots of repair manual do not give the specs for piston protrusion , but your machinist can get them for you. Even a crank shaft grinder can shorten or lengenten the stroke by a few thousands and you may not catch that.

If the hole in the rod isn't round that hone won't force it round it will just make it look nice. Been there had that done to a VW rod more than 40 years ago. Army buddy had one that had worn through the insert. "Machine shop" refurbished it. Engine still knocked. The fourth time the engine came apart I put a dial caliper on the rod in line with the wear and at right angles. It was out of round. By then the crank was worn more and a new rod didn't cure the knock.

Gerald J.

I am like you I try and do most things by myself. but sometimes am limated to motor machine shop work. I have had some good experiences, and some not so good. Stan

First, a word about machinist---I am a tool and die maker and a mechanic. Three different machinist can get three different readings especially for "inside measurments".
Plastigauge should be used for your final measurment.

I agree with your comment on plastigauge but not inside mics. When I was a machinest in a factory we all had to measure IDs the same if we didnt we didnt have a job very long.Outside of plastigauge the only real way to measure IDs is with ID mics or telescoping gauges

One thing you have to watch for is a favorite trick of "good 'ol boy" corner machine shops, is to cut the rod caps on a slight angle to the center, so it pinches the rod in a bit to make the hole smaller, and then hone it to size- you can usually tell when it's been done, as it'll be a b!$ch to get the rod cap off, as the rod's been tweaked out of shape by the force-fit

Just cause U got a lathe or milling machine, that don't make U a machinist.

ALWAYS USE A BORE GAGE TO CHECK THE INSIDE DIMENSION OF SOMETHING. Or at least a telescope gage.

Yes it does. I've checked roundness, before and after. You have to shave some metal off cap and rod mounting surface. That closes it up and creates a slight oblong. Not any different then what happens when you take shims out of a babbit bearing assembly.

You shave, shrink the hole, and then bore back to round and the proper ID. It is standard procedure for high-hour diesels. Everytime you do it, the rod gets slightly shorter, so there are limits.

Plastigauge is where this all started. Got .0035" to .0045" clearance and was thinking about installing new bearings. But they are not marked and I've been trying to find out what undersize they are. Factory specs call for a max. worn clearance of .0037"

Yes, that is a problem we often had to deal with. Whenever you resize a rod on the big end, it effectively becomes shorter. That's why it's usually kept at a minimum, and if too bad - the rod gets replaced with new.

Deere engines were critical, and often all it took was a drop of piston height of .005" to effect cold weather starting.

I guess if you also line-bored the mains, you get it back buy moving the crank closer to the top? Never did it, just thinking about it. If the crank actually got moved by line borning, then there be issues of timing gear backlash to deal with.

(quoted from post at 18:52:35 01/08/10) I agree with your comment on plastigauge but not inside mics. When I was a machinest in a factory we all had to measure IDs the same if we didnt we didnt have a job very long.Outside of plastigauge the only real way to measure IDs is with ID mics or telescoping gauges

Click to expand...

We are not talking about "Factory" or Tool and Die shops. There are many level classifications for Machinist, just as in other trades.

Yup!

JD, the method you used to check the bearing shell thickness is pretty much identical to the way we did at our engine plant. The only difference is we used a gage ball, a known size. We also had ball mikes, with special anvils for these jobs. A guy machining something 1/8 off is plain dumb. There used to be a couple of decent guys doing machine work around here, but few people are rebuilding anything anymore. Mostly they just buy a reman or crate engine.

It dont make any different if its a factory or a tool and die shop,your right,but what I was saying was that a machinist should get the same reading on ID mics as the next machinist would.

I'm a retired machinist with 40 years experience. Two years ago I was lucky enough to find a small lathe at an auction. It came with a milling attachment and quite a bit of tooling. So far I have bored a connecting rod for a styled A, and a set of manifold studs for a 1945 "H". We are now in the process of building a machine to spin mags. We have also built a machine to polish crankshafts. I have also done other work on the machines. rw

Alright I have been looking at this and am no machinist either.You have about .0015 too much clearance or a little less?If its the same on the top then would it be .0030 too much clearance.So when you get the right bearings the inside diameter will be .0030 smaller than the ones you have now or each shell will be .0015 thicker than the ones you have now.Also if you check it in 3 places on the journal does it get better or worse?Are all of them the same or are some different?If all of them are close to the same maybe,and this is a long shot,but maybe you need a shim thats.0015 thick?Old stuff might have been shimmed but I kind of doubt a Continental engine would be.I vaguely remember some engine needing shims before,maybe an Allis in the 1930s or 1940s.

Glad it all measured up. And in the end it does make total sense that the mains were ground the same as the rods.

Your not alone in having engine machine shop problems ! I have had more then my share of them too !
Best thing I ever did was to get my own mics and a straight edge that is pretty close to being straight. I try to double check EVERYTHING I have someone do for me.