The Engine Rebuild Kit
by Curtis Von Fange
I always liked engine rebuild kits. They have all the replacement parts for overhauling an engine without going
to the store to get gaskets, special measuring tools, or miscellaneous parts. They come neatly packaged, clean and
tidy. But it's important not to let that packaging lull you into a false sense of security. The appearance of
matching sleeves, pistons, rings, and bearings can cause frustration and agony if not properly measured and
installed in a workshop environment. Following certain assembly procedures will reaffirm how wonderful these
engine kits are. This paper is certainly not exhaustive in the engine assembly procedure, but will, hopefully,
point out a few of the pitfalls that might be bypassed under the guise of a 'rebuild kit'.
Engine cleanliness isn't next to godliness, but it oughta be. Removing all the oil and built up grime on engine
parts will ensure the longevity of any rebuild project. Sending out the head, block, and major grease-carrying
components to be professionally hot-tanked will remove ages of built up grime and internal rust. Smaller parts can
be cleaned in the shop using a solvent tank, then dried, inspected for integrity, and laid on top of a clean rag
(an old sheet works good for this). When the engine comes back from the machine shop it should, ideally, be put on
a rotating engine stand and prepared for reassembly. Use an air (air compressor) gun to blow off the engine block
along with all the openings and bolt holes to remove any residue. A clean solvent rag can be used to wipe off the
internal surfaces to remove any film left over from the tanking process. Hopefully the machine shop has
reinstalled the casting plugs (sometimes called freeze plugs) and the oil galley plugs.
The first item of business in the kit is to install the cylinder sleeves. I recommend that the machine shop
install these, but, if they didn't, here is the best way to do it. First, stick them in the freezer for a couple
of hours. This will cause the metal to shrink just enough to slip into the cylinder bore a little easier. Place
the block on a hydraulic press and line it and the ram up with the sleeve. Place some cylinder sealer around the
upper end of the sleeve, install an adapter on the top of sleeve which will mate to the ram and quickly but gently
press the sleeve into the bore. Don't stop midway to answer the phone or talk to the dog as the natural heat from
the block will quickly cause the sleeve to expand thereby increasing the risk of breakage. Only stop when the
sleeve is flush with the top of the block. Go ahead and repeat the process with the other sleeves. If, like most
ill equipped barn shops, you don't have access to a press, you can use a block of wood and a large sledge hammer.
Make sure and get an extra set of hands to hold everything reasonably straight; and tap lightly but firmly with the
hammer and watch your hands.
Now that the sleeves are in place the next step is to match the pistons to each cylinder. Take the manual and
locate the piston to cylinder wall measurement. Generally it should be around .004 to .007 sidewall clearance.
Then locate an industrial supply house (or a very well stocked automotive store) and purchase a very long feeler
gauge, commonly called a ribbon gauge. Get at least two sizes, one about .002 and another about .004. Intall the
piston in the bore and see if the thinner feeler gauge will slip in next to the piston. The proper fit is when the
ribbon gauges can be pulled from between the piston and sleeve with a specified inch-pound pull using an inch/pound
scale. Of course our shop didn't have the scale so we gauged it with a mildly firm pull; the feelers slipped
freely out of from between the piston and cylinder sleeve without binding. You should check the piston at the top
and at the bottom of the cylinder for proper clearance in case the sleeve is tapered. (Don't assume that if the
piston freely falls through the bore that the clearance is adequate. I did that with an engine kit once. Turned
out that after the engine ran for four or five minutes the piston heated up enough to expand in the sleeve and
freeze up the engine.) If the clearance is inadequate the cylinder bore (or sleeve) will have to be honed and then
rechecked. Take the time to do it right.
Each piston will come with a certain number of piston rings. Unwrap the rings and lay them next to each piston in
the order of installation. Now it is time to check the ring gap. When the ring is in the cylinder bore it has to
have a specified compressed gap; in other words an opening between the ring ends. Consult the manual for this
spec. Generally, it is considered to be .002-.003 per inch of cylinder bore diameter. Install the first ring in
the bore, take the piston, invert it, and gently slide the piston in the bore pushing the ring approximately half
way down the sleeve. Take your feeler gauge and measure the end gap clearance. Compare with the specs and
determine any necessary changes. Insufficient clearance will require that the ring gap ends be filed down to
tolerances. Take a file and mount it vertically in a vise. Take the ring and, holding it firmly in both hands,
draw it downward over the stationary file. Remove some metal and check the ring in the bore again. Repeat as
needed. Follow this procedure for each ring making sure to note each gap specification for each particular ring.
After the gap for each ring is corrected then take each ring and check the ring to corresponding ring groove in the
piston. There should be ample room for the proper feeler gauge between the ring and groove. Again, check the
manual for this spec. Too tight a fit will keep the rings from proper rotation and movement as the piston moves up
and down. Make sure and place each ring in corresponding order with each piston groove; check the ring for a mark
indicating the correct side up. They are now a matching set. This is an important step in the engine assembly
because as the rings heat up they will also expand. Insufficient clearances will cause extreme scoring of the
cylinder wall, ring breakage, and potential engine seizure.
The next step in assembly is to check the piston pin to bushing tolerances. Once again, this is a very close
tolerance and should best be done by a competent machine shop. An insertion pressure of pin to bushing will be
slightly looser than that of the pin to piston. When dealing with clearances of .0002 or less it is important to
have the proper measuring tools. A pin too tight or too loose will cause a piston and rod to literally break apart
under the stresses of motor operation.
It is recommended that the head be reworked in its entirety by the machine shop. Tools for magnafluxing the head
for cracks, pressing guides in and out, getting the correct angles on the valve seats, setting the proper valve to
head recession setting, measuring and milling warped surfaces, amongst other things are really beyond the scope of
a doing a lasting engine rebuild on the home shop level.
Crankshaft and camshaft measuring, grinding, and polishing is also out of the realm of the home shop. It is wise,
though, to always double check the machine shop's work with a feeler gauge, dial indicator, and/or plasti-gauge. A
while back I had a machine shop measure the main journals and order the mains for an engine I was working on. I
later found out after engine completion that my low oil pressure was due to a mis-reading of the micrometer that
the machinist made in between his phone calls. The mains were .010 off. A plasti-gauge reading caught the mistake
though it was after a post run break-down. It is important to check the crank end play with a feeler gauge and
also to check each bearing journal with plasti-gauge before starting the reassembly procedure. It's amazing how
many of these specs can be found in the manual when you know what to look for.
One additional point worth mentioning is to make sure that the oil pump is primed before buttoning up the bottom of
the engine. It is recommended that the pump be disassembled and packed with a lithium based grease commonly called
'white lube'. If the pump cannot be conveniently disassembled then take the white lube and squeeze it into the
intake port of the pump. Rotate the pump in the direction that the engine would rotate the pump and continue to
squeeze the grease into that port until the pump gears are adequately primed. It is imperitive to have oil
pressure in the motor before it is actually started up. Priming the pump will facilitate rapid charging of the oil
As I mentioned earlier this is not a comprehensive engine assembly list. These points are to encourage the
mechanic using an engine rebuild kit to make sure to check and verify the tolerances of all the moving parts. Just
because the kit looks good doesn't mean that everything will go together the way it should. Taking the time to
check all the above tolerances will ensure that the kit will do what it was designed to do: make the engine run
right the first time.
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