As others have covered what line boring is I'll just quickly mention what they
do when re-sizing your con rods.
A good shop will start by cleaning, shot blasting, magna fluxing for cracks,
and testing for straightness. Then they remove a small amount of material from
the mating surface of the cap and rod, the rod is usually fitted with new rod
bolts, then they are torqued to manufacturers specs, then the opening is
re-machined to manufacturers specs. Next the small end is re-bushed and reamed
to size parallel to the big end. When all this is done you have rods that have
perfectly round holes that are perfectly parallel between the big and little
end and all your rods will be the exact same length.
There two occasions where you must have your rods re-sized. First is when you
change your rod bolts the big ends were sized at the factory with the original
bolts and any time the bolts are swapped or new bolts are used you run the risk
of distorting the big end. The second is when you have your engine balanced you
have to have your rods at least checked to see that everything is perfect or
you're wasting your money on balancing. If your rods aren't straight and the
same length your engine won't be balanced. Even the slightest difference in
length between rods will throw off the balance of your motor because it moves
the weight of the piston out of relationship with the crank, as well as
changing the compression height of the piston in the cylinder. Considering this
is one of the cheapest operations a machine shop will do for you I highly
recommend it.
My $0.02
Doug Hamilton
1960 Triumph TR3A
1963 Fiat Cabriolet
Subject: RE: Line boring???
>> I was talking to a mechanic friend of mine yesterday about
>> the rebuild work on the TR motor. When I told him the crank was a
>> replacement he suggested there may be problems with fitting this to
>> another engine and perhaps the rods need to be line bored to match
>> the rods. Anyone throw light on this process, and do I really need to
>> take it on board.
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