Line boring

[Richard from SE AZ]

Going to make a couple of calls tomorrow about a 2N block. I have read posts about line boring a block that is being rebuilt. What is that all about and when is it necessary to do?

 

[lha]

When you change oil pumps,bearing caps,etc.,then the chance of the new one being exactly the same is remote.For that reason,the block,caps on is bored to assure that the block is dead straight,for the crank to fit with minimal interference from out of alignment.Hope that explanation helps.---lha

 

[NOXJohn]

All three main bearing caps need to be bored so the holes are exactly in line and the correct circular diameter. The crank is held in place by the mains and there is little or no room for error. My understanding is that when the block was built the main bearing caps were bolted on the block and then a boring rod ran through all three caps to insure alignment. Therefore it is best to have all three main bearing caps that came with the block when it was manufactured. If you don't it is best to have a machine shop check the line bore and re-bore if necessary. If not you could have main bearing problems. However, others have told me that if the crank does not bind after mains are torqued down and bearings plastigage correctly that you don't need to get the line bore checked. I have that situation presently with a cranked front main cap on a front mount that I am rebuilding. I got a replacement from John Smith. I found it difficult to find a shop that can line bore a block. The two that I found change around $200.

 

[Welding man]

I have rebuilt a lot of N engines and have never had to have one line bored.When you tore it down if the old bearings didn't have a odd wear pattern and the crankshaft checked out OK or even if you had the crank reground. Install the new bearings, plastiguage them,if the clearences check out and the crank turns free it will be OK.

 

[oldtanker]

(quoted from post at 22:21:12 02/01/11) Going to make a couple of calls tomorrow about a 2N block. I have read posts about line boring a block that is being rebuilt. What is that all about and when is it necessary to do?

Line boring is done as described. The reason for line boring the same. The thing is that most engine blocks don't warp. About the only time you have to line bore a block is when you are working with a block that is susceptible to warpage.

Rick

 

[TheOldHokie]

(quoted from post at 01:21:12 02/02/11) Going to make a couple of calls tomorrow about a 2N block. I have read posts about line boring a block that is being rebuilt. What is that all about and when is it necessary to do?

line boring is needed when one or more of the main bearing caps is damaged or replaced. The front main bearing cap is also the oil pump body and that is the usual source of a problem if there is one - not common but it does happen. Bearings can also spin in the block bore wearing the bore out oversize necessitating line boring to bring it back to specification. Simply ask your machine shop to double check that the caps are all correct - never know who was in there before you and verify the bore is undamaged. Line boring the mains alone is going to cost something in the vicinity of $200.

One other place that line boring might be required is the cam way. The cam runs directly in the cast iron block - no bearings - and the bore can become worn oversize. This is an area that is almost never checked by most guys rebuilding an N motor. Have the shop check it to make sure it is within specs. If it is worn oversize and/or the cam is worn undersize the rebuilt engine will likely have marginal oil pressure. A worn cam can be replaced with a new one for about $150. A worn block can be line bored and camshaft bearings installed. Neither is cheap but a quality rebuild seldom is and there are a lot of complaints here about low oil pressure on rebuilt motors. These motors are 60+ years old and I'm pretty confident Ford never expected them to be in service that long. If they did the cam way would have had bearings in it. Recent discusiions have suggested the camshaft bearings used in the 39-53 Ford flathead V8 (Clevite SH-21S) can be fitted to the N block if needed. Next N motor I rebuild I'm going to to do this just to say I did.

TOH

 

[rnorum]

Good answers,you can also line hone most blocks to get main cavities on size (costs less) but if you install a new front cap it probably wont alighn good so you will have to then line bore, around here MN WI about $150. In the past someone may have filed the caps and or the center main cavitiy can be pounded out 3 more thous and still look good.If your going to use plastigauge use without rear main seal to be more accurate at room temputure

 

[oldtanker]

(quoted from post at 06:36:32 02/02/11)

(quoted from post at 01:21:12 02/02/11) Going to make a couple of calls tomorrow about a 2N block. I have read posts about line boring a block that is being rebuilt. What is that all about and when is it necessary to do?

line boring is needed when one or more of the main bearing caps is damaged or replaced. The front main bearing cap is also the oil pump body and that is the usual source of a problem if there is one - not common but it does happen. Bearings can also spin in the block bore wearing the bore out oversize necessitating line boring to bring it back to specification. Simply ask your machine shop to double check that the caps are all correct - never know who was in there before you and verify the bore is undamaged. Line boring the mains alone is going to cost something in the vicinity of $200.

One other place that line boring might be required is the cam way. The cam runs directly in the cast iron block - no bearings - and the bore can become worn oversize. This is an area that is almost never checked by most guys rebuilding an N motor. Have the shop check it to make sure it is within specs. If it is worn oversize and/or the cam is worn undersize the rebuilt engine will likely have marginal oil pressure. A worn cam can be replaced with a new one for about $150. A worn block can be line bored and camshaft bearings installed. Neither is cheap but a quality rebuild seldom is and there are a lot of complaints here about low oil pressure on rebuilt motors. These motors are 60+ years old and I'm pretty confident Ford never expected them to be in service that long. If they did the cam way would have had bearings in it. Recent discusiions have suggested the camshaft bearings used in the 39-53 Ford flathead V8 (Clevite SH-21S) can be fitted to the N block if needed. Next N motor I rebuild I'm going to to do this just to say I did.

TOH

Yup he's right. I haven't replaced a bearing cap in 20 years but it happens and then it will need bored for that too. I've rebuilt 8 or 9 engines in the last 15 years or so and never worked on anything that required line boring in that time frame. Only one I know of is my brother in laws German diesel 826 IH. Those have to be lined bored for the cam every rebuild. He's done it twice in the last 15 years. Once do to wear (11,000 original hours) and once to being cheap (got told the first time that his injector pump was going and he didn't want to spend the money at the time, 200 hours later it went and cost him the rebuild).

I'm planning on going through my 8N this spring. I'll have it done if need be.

I'm also doing a 151 GM "Iron Duke" that the block will be bored but will not require line boring.

Rick

 

[John (TR)]

The nachien shop I go to insists on checking which is like 20.00 and only bores if needed. The 40 I recently rebuilt had oil pressure problems and the check found that the front cap was off .007 which is huge. The moral of the story is you don't really know what the last guy did, and in my case 20.00 is cheap insurance. In my case the if a line bore is needded the 20 is absorbed into the cost and you only pay for the lne bore at stated cost which for me was 100.00