The Stovebolt Site Forums The Shop Area General Truck Talk reassembly of 56 235 just back from the machine shop

I'm going to start this weekend. The block had been bored .060 over when i got it, looks like a recent rebuild, but the re-used the original cam and did a poor job on the head. Had the block cleaned, cut the crank .010, new 261 cam, the .060 pistons were ok, so had the shop install new rings and lightly hone the cylinders. Head gone completely thru w/new seats and exhaust valves, the intakes were ok. I am going to install the crank w/the new bearings dry, ck bearing clearence w/plastigage and see where I'm at. The front main bearing had a .002 brass shim on each bolt when I pulled it apart. I have shim stock to set bearing clearance. I have downloaded the 56 truck manual from Keith Hardy's site, but it cuts off the side of the page. I need to know the main bearing clearances if someone can post. The machinest said I did not need to ck the rod clearances?. I could use some comments on basic re-assembly, since I've never put a motor together. I have a ring compressor, so after I get the main bearings set, I will coat the crank and bearing w/assembly lube and move on to the pistons. I know I need the ck the thrust bearing clearence also. Any comments appreciated.
Dave

Shop manual specifies .0015"-.004" but I would'nt go lower than .0025". Plastigauge tells you for sure what you've got. I would check and re-torque them all to be sure. Any time a new motor siezes it's usually from improper use of measuring tools.
End play should be .009" max. if I remember correctly. I set all mine at .003" and it's quiet after break in. Make sure the flywheel is nice and flat on the drive surface when you mount it and check for runout on the trans. mounting hole in the bellhousing.Good luck.

Curt B.

On the valves,Putting so much money into the engine.If the intakes looked good or not I would have replaced them.also new valve guides.Its the old story,pay me now or pay me later.Please don't get me wrong.It's just my thoughts

Dave s,
I would be careful if I found shim stock under a bearing cap. When all is done properly, a .010- crank takes .010- main brgs..the machine shop grinds mains and rods to specs so the customer can get over the counter undersize inserts to fit! Should be no guessing or shimming! Check the two bottom bolts that hold the timing cover on. They used to be installed from INSIDE the pan. You can drill and tap them for installation from the outside. If you ever want to pull the cover, it can be done without pulling the pan.

Stuart.

The shim was under the bearing cap when I dis-assembeled the motor, so I'll just ck w/plastigage and see. I have the undersize bearings. The head was ck'd and the exhaust valves and guides were replaced. The machinest swears the intakes and intake guides are ok. Head lightly surfaced to make sure it's flat and hardened seats installed.

I don't think that the mains were shimmed in the 56 motor. I would be checking without the shims.

truckernix,
I might be mistaken, but the only motors I have seen with any shims had poured bearings. Insert bearing motors rely on journal size/insert size to correctly set clearance.

Stuart.

Hello Bolters,
Dave I overhauled a 235 years ago.I had crank turned .010 under because of journel condition and when I instaled it in the block and torked the caps it would not turn even tho I had correct clearence.Mecanic friend said I needed to have block line bored-this is where the machine shop installs main bearing caps and bores stright through to make sure they are tru.Well I didnt take his advice and i shimed it where it was nessary to make it turn,man that engine ran better than new for 2 months and then It siezed # 3 main bearing.When i do my present 235 there will be no shims.Good Luck Aaron

The early 54 was the last 235 that was designed for use with shims. The engines after that did not use shims. If you have any bearings that are not within spec, contact the machinist.

Plastigage is not that great for checking clearances. Too many variables that can mess up the readings. The correct method uses micrometers and snap gauges. It's okay for a street engine, but if you're building a performance engine the mechanical measuring tools should be used.

Fred,
I would like to know what those variables are when using plastigauge. I know the method of mechanical measurement is subject to many variables. Among them are when were the measuring tools calibrated and by who? To what standards and level of precision? Are they cheap or high quality tools? Temperature also affects expansion and contraction of both the measuring tool and pc. If you walk around with a mike in your hand it will measure different from one on a bench. What about wear and tear on the machine tools? How old is the crank grinder? How old is the boring mill and when was the last time it was squared up? How do you know the “machinist” didn’t gorilla tighten the block, machine it, measure it, and then distort it when he removed the clamps? What if some hack millwright “reconditioned” these machine tools? There are no guarantees that a line bored block is actually in a straight line parallel to the head surface. Brand new machine tools aren’t even square and wear is a constant. Every machinist has their own idea of the proper friction required between a measuring tool and pc. and I can guarantee you there is no consistency. Measuring a journal with one tool and measuring bearing thickness with another and then measuring a bore and determining a mathematical clearance is only an educated guess and introduces 3 variables. At least once a week I have to kick a machinist in the [censored] because his parts don’t meet tolerance when double checked on a coordinate measuring machine although he will swear he checked and calibrated his tools. Plastigauge is the only method that exactly confirms the amount of clearance. This is why there is a tolerance range in the first place as variation with measuring tools is assumed to be present. Sadly I believe there are many victims of shoddy machine work who don’t know any better. There are many machinists who are complete hacks and will bore blocks crooked, out of square, with improper fits, etc. If a cylinder is bored .003” bigger than the rest some won’t tell you they made a mistake and order new pistons/rings. They will give you some b.s. story about a defective piston causing that slapping sound. When an engine seizes and the machine shop swears all tolerances were met they believe it as their tired and inconsistent measuring tools told them so. However failure only happens if the tolerances were truly not met. I have been training machinists for the last 15 years and have seen every excuse related to the cutting tool, the machine tool, and the measuring tool. Experienced millwrights will confirm the reliability of plastigauge as in larger industrial applications micrometers become unpractical. Sorry to all for the long rant but let’s remember not all machinists are skilled ones. Confirming clearances with plastigauge is cheap, accurate insurance in my opinion.

Curt B.

Just to clear up a point here, the motors in the early fifties up to 53 had insert main bearings with shims. I believe that there examples of this in the shop manual. I have a set of NOS main bearings with the shims and original instructions on how to shim them.

truckernix,
I just learned something..thank you.


Stuart.

It beats me why they made a precision insert bearing and used shims. I get the impression that they all came from the factory with the same number of shims so it wasn't a tolerance problem. It sure is an interesting piece of history, isn't it?