Line Bore or Not

[Anonymous-0]

From time to time ? comes up on needing to replace the oil pump on an N. It came up again yesterday and there were replys that said you will need to line bore when you replace the oil pump. By line bore do you mean gut the block and take to the machine shop? Cause that to me is line bore. I have never did that,I fill the pump gears with grease. I plasta guage, to .003 or less, put in a new front seal it is off set and a bit proud, a little PVC on it, new pan gasket, fill with oil, start and get oil pressure and done In past post some have said no need to line bore and they like me say never had a problem. I am a do it right guy but have taken my share of short cuts like everybody. Does it say in any Ford manuels to line bore? I must have missed it. I would hate to be the newby and with a shady tree diploma (thats me) and see just needing a new oil pump and find out it is a major repair. Ya or Na right or wrong.

 

[Bill Rowles]

Good question....I have wondered the same thing. Maybe since the historic good practice on engine repair has been to send the block to the machine shop any time the main bearing cap is replaced with one foreign to the unit, we should ask if anyone replacing the oil pump in the Ford "N" tractor has had a main bearing failure result from not align-boring the block with the new/replacement pump unit? Maybe the configuration and machine tolerances used by Ford and the persons making replacement parts are good enough to assure successful replacement without reboring the main bearing journals.

 

[NOXJohn]

I have rebuilt four 8N engines. All the blocks were sent to a machine shop for the normal work. Three were not line bored. The Fourth engine had a cracked front main bearing cap. For that I got a replacement cap and had the block line bored. All four engines run great and carry good oil pressure. The one that was line bored is the best. The oil pressure needle responds immediately when the engine is cranked, regardless of how long it has set. The needle goes to 35 lbs and stays there. Even at idle it carries 25+ Lbs. If and when I rebuild another N engine I will have it line bored. However, I had a very difficult time finding a machine shop that could line bore. Most in my area did not have the equipment. I finally found a shop 45 miles away that could do it.

 

[Ken(Ark)]

If you replace a main cap , you must line bore , unless you are the one in a million exception .

If you are rebuilding a motor with original parts replaced in the original order , then the odds are strong that it will not need line bored .

 

[TheOldHokie]

(quoted from post at 02:56:35 03/26/13) From time to time ? comes up on needing to replace the oil pump on an N. It came up again yesterday and there were replys that said you will need to line bore when you replace the oil pump. By line bore do you mean gut the block and take to the machine shop? Cause that to me is line bore. I have never did that,I fill the pump gears with grease. I plasta guage, to .003 or less, put in a new front seal it is off set and a bit proud, a little PVC on it, new pan gasket, fill with oil, start and get oil pressure and done In past post some have said no need to line bore and they like me say never had a problem. I am a do it right guy but have taken my share of short cuts like everybody. Does it say in any Ford manuels to line bore? I must have missed it. I would hate to be the newby and with a shady tree diploma (thats me) and see just needing a new oil pump and find out it is a major repair. Ya or Na right or wrong.

When an engine block is manufactured the caps are bolted to the block and the mains in the block are bored end to end in a single pass. That is line boring.

The result of that operation is main bearing caps that are matched not just to that individual block but to they main bearing they are on. The center line of the crankshaft bore is off slightly from the parting line of the caps and/or offset to one side which means the two halves are not perfect semicircles. Reversing or swapping the caps around or using caps from a different block will result in an out of round bore at that point on the crankshaft center line. That is a real no-no resulting in binding of that bearing, premature failure, and possible journal damage.

When a cap has to be replaced the parting lines on the cap and block are ground down a few thousandths to reduce the diameter of the bore, the caps are bolted to the block, and the block is rebored to the factory diameter correcting any out of roundness.

TOH

 

[TheOldHokie]

(quoted from post at 07:12:07 03/26/13) I have rebuilt four 8N engines. All the blocks were sent to a machine shop for the normal work. Three were not line bored. The Fourth engine had a cracked front main bearing cap. For that I got a replacement cap and had the block line bored. All four engines run great and carry good oil pressure. The one that was line bored is the best. The oil pressure needle responds immediately when the engine is cranked, regardless of how long it has set. The needle goes to 35 lbs and stays there. Even at idle it carries 25+ Lbs. If and when I rebuild another N engine I will have it line bored. However, I had a very difficult time finding a machine shop that could line bore. Most in my area did not have the equipment. I finally found a shop 45 miles away that could do it.

John, If you don't mind sharing how much did Gunther's charge for the line boring?

TOH

 

[ASEguy]

Anytime a main cap is replaced it must be either align honed or align bored to insure correct main centerline. The main saddle can be checked by using a straight-edge on the saddle and trying to fit a .0015 feeler gauge under the straight-edge. If you can't, the main saddle is good. That says nothing for the caps. Main and rod caps must go back on in the same position and direction to ensure proper centerline of the crank. Align honing insures perfectly aligned bores of the proper diameter to ensure proper bearing crush. Damaging bearings is the least of the problems. Cracking crankshafts at the filet area is more common in my experience. They produce a double knock similar to a rod knock as the combustion event applies pressure then releases it. Have it aligned bored and be happy. I've never regretted doing the job right. Hope this helps. Gerard

 

[NOXJohn]

I went to Mark Small Machine, Inc in Westminster,
MD. His was the closest shop I could find that could
line bore. He charged $180 to align bore the mains.
That was September 2011. He also did all the other
machine shop work for that rebuild. He has one
fantastic shop. He seems to do a lot of high
performance engine work. Expensive but very good
work.

 

[JMOR]

.............................and then there is the guy a day or two ago talking about how he ran one for 8 years with a piece of a leather belt in place of a rod bearing. MUST!

 

[W_B]

(Out of apparent ignorance) I replace the oil pump on my '41 9N about 15 yrs. ago without doing the line boring. It runs about 25 lbs. on start up and 20 hot after replacement and now. Given the age and condition of the machine I doubt I would have done it differently had I known anyway. No problems have cropped up since then, that I know of, so I guess sometimes you get lucky.

 

[Dean]

No need to align bore if you simply rebuild your existing oil pump.

If, however, you want to have good hot idle oil pressure you will likely need to replace the oil pump housing, which is integral with the front main bearing cap.

If you do so, it is ABSOLUTELY ESSENTIAL that you have the block align bored, unless you are the luckiest man alive.

Dean

 

[Ronnie Graves]

when I got the front main cap/oil pump assy in the box were the instructions "to have cap and engine line bored cap is an un-finished part and must be fitted to the engine"