Line boring a block?
Discussion
Is the engine going to run stock or performance?
If stock then you could start by assembling all the other bearings and check the crank for free rotation. At the same time check each of them for clearance using 'Plastigauge'.
Dis-mantle and re-assemble including the first of your suspect caps and shells. Again check for free rotation and clearance. Repeat for the second cap.
If all is running smooth and the clearances are similar then you got away with it.
If you are building a performance engine you could do as above but considering the costs involved in the rest of the build it would perhaps be false economy.
Steve
If stock then you could start by assembling all the other bearings and check the crank for free rotation. At the same time check each of them for clearance using 'Plastigauge'.
Dis-mantle and re-assemble including the first of your suspect caps and shells. Again check for free rotation and clearance. Repeat for the second cap.
If all is running smooth and the clearances are similar then you got away with it.
If you are building a performance engine you could do as above but considering the costs involved in the rest of the build it would perhaps be false economy.
Steve
I hate it when bits go missing that make an otherwise perfectly good bit of kit next to useless. I used to get it quite a lot with Pug 205 cylinder heads where someone had lost a cam cap or broken one by trying to fit it the wrong way round. Anyhoo, your chances of a cap from another block being a perfect fit is slim to none but I guess you could get lucky. Maybe if you had ten sets to pick from.
Line boring would sort it as long as you make sure it hasn't already been line bored at the factory. You can generally only get shells in the one oversize on the o/d.
At least tell the seller it's worthless without the right caps and get the price down to cover the cost of line boring it.
Line boring would sort it as long as you make sure it hasn't already been line bored at the factory. You can generally only get shells in the one oversize on the o/d.
At least tell the seller it's worthless without the right caps and get the price down to cover the cost of line boring it.
Pumaracing said:
Line boring would sort it as long as you make sure it hasn't already been line bored at the factory. You can generally only get shells in the one oversize on the o/d.
Yes my thoughts entirely.I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Not sure if oversive OD shells are availble for this motor.
I reckon as it is the block has very little value.
Huntsman said:
Pumaracing said:
Line boring would sort it as long as you make sure it hasn't already been line bored at the factory. You can generally only get shells in the one oversize on the o/d.
Yes my thoughts entirely.I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Not sure if oversive OD shells are availble for this motor.
I reckon as it is the block has very little value.
Huntsman said:
Yes my thoughts entirely.
I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Ummmm, maybe it's time, 20 years or otherwise, to think using about a new engineering firm with slightly smarter primates working for it! If the caps from another engine were perfectly in line laterally but a bit too large vertically because the split line wasn't in just the right place then ok. However, as the caps from another engine are absolutely certain to be more out of line laterally than they are ever going to be vertically then shaving a few thou off the faces of them won't make a rat's arse of difference to that. You'll still end up with a cap that's out of line on one side where the boring bar never touched it because, well ummm, it was out of line on that side!I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Now I could go into a vast amount of detail about the mathematics of chord theory as applied to semicircles but I'd just send everyone in here other than university level maths graduates to sleep. However I can run the calculations because for reasons that now escape me one of the hundreds of computer programs I've written over the years to help with my race engine designing just happens to be one that solves these particular equations.
If the cap from say a 64mm diameter bore was misaligned by only 10 thou (0.25mm) laterally how much would you have to mill off the split line to bring the width of the entire cap within the bounds of the lower half of the semicircle so you could line bore it back to size and touch every part? Obviously you need to bring one side back by 0.25mm so therefore the other side will come back by the same amount so you want the chord across the base of the cap to now be 63.5mm long instead of 64mm long. With me so far?
The answer is 4mm! A non trivial amount. You've now lost a good part of the bearing tang retention slots so the bearings won't fit and the main bolts might even bottom out in their holes. Arse! So machine new bearing tang retention slots and shorten the bolts a tad. However, never have done this before you don't have a cutter to machine something like a bearing tang retention slot so you tell the customer it's a bit more complex than you thought, for reasons that you couldn't possibly have worked out in advance because you take your lunch breaks in the trees and answer to the name Cheetah and add another £100 to the bill. However, even having done all this, and maybe even correctly, you've still bored the top of the cap thinner by 4mm which is probably 1/3 of its original thickness so it breaks when the engine gets up to peak rpm and the crank flies out and lands in the road. Luckily the engine stops at the same time so you don't have too far to walk back and pick the crank up!
I could continue in this vein for some time but I'd only be gilding the tulip or whatever it is that us enjineers wot actually studied maths say when we're pontificating.
tr7v8 said:
Huntsman said:
Pumaracing said:
Line boring would sort it as long as you make sure it hasn't already been line bored at the factory. You can generally only get shells in the one oversize on the o/d.
Yes my thoughts entirely.I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Not sure if oversive OD shells are availble for this motor.
I reckon as it is the block has very little value.
Pumaracing said:
Ummmm, maybe it's time, 20 years or otherwise, to think using about a new engineering firm with slightly smarter primates working for it! If the caps from another engine were perfectly in line laterally but a bit too large vertically because the split line wasn't in just the right place then ok. However, as the caps from another engine are absolutely certain to be more out of line laterally than they are ever going to be vertically then shaving a few thou off the faces of them won't make a rat's arse of difference to that. You'll still end up with a cap that's out of line on one side where the boring bar never touched it because, well ummm, it was out of line on that side!
Now I could go into a vast amount of detail about the mathematics of chord theory as applied to semicircles but I'd just send everyone in here other than university level maths graduates to sleep. However I can run the calculations because for reasons that now escape me one of the hundreds of computer programs I've written over the years to help with my race engine designing just happens to be one that solves these particular equations.
If the cap from say a 64mm diameter bore was misaligned by only 10 thou (0.25mm) laterally how much would you have to mill off the split line to bring the width of the entire cap within the bounds of the lower half of the semicircle so you could line bore it back to size and touch every part? Obviously you need to bring one side back by 0.25mm so therefore the other side will come back by the same amount so you want the chord across the base of the cap to now be 63.5mm long instead of 64mm long. With me so far?
The answer is 4mm! A non trivial amount. You've now lost a good part of the bearing tang retention slots so the bearings won't fit and the main bolts might even bottom out in their holes. Arse! So machine new bearing tang retention slots and shorten the bolts a tad. However, never have done this before you don't have a cutter to machine something like a bearing tang retention slot so you tell the customer it's a bit more complex than you thought, for reasons that you couldn't possibly have worked out in advance because you take your lunch breaks in the trees and answer to the name Cheetah and add another £100 to the bill. However, even having done all this, and maybe even correctly, you've still bored the top of the cap thinner by 4mm which is probably 1/3 of its original thickness so it breaks when the engine gets up to peak rpm and the crank flies out and lands in the road. Luckily the engine stops at the same time so you don't have too far to walk back and pick the crank up!
I could continue in this vein for some time but I'd only be gilding the tulip or whatever it is that us enjineers wot actually studied maths say when we're pontificating.
Its a 1965 Ford Windsor V8.Now I could go into a vast amount of detail about the mathematics of chord theory as applied to semicircles but I'd just send everyone in here other than university level maths graduates to sleep. However I can run the calculations because for reasons that now escape me one of the hundreds of computer programs I've written over the years to help with my race engine designing just happens to be one that solves these particular equations.
If the cap from say a 64mm diameter bore was misaligned by only 10 thou (0.25mm) laterally how much would you have to mill off the split line to bring the width of the entire cap within the bounds of the lower half of the semicircle so you could line bore it back to size and touch every part? Obviously you need to bring one side back by 0.25mm so therefore the other side will come back by the same amount so you want the chord across the base of the cap to now be 63.5mm long instead of 64mm long. With me so far?
The answer is 4mm! A non trivial amount. You've now lost a good part of the bearing tang retention slots so the bearings won't fit and the main bolts might even bottom out in their holes. Arse! So machine new bearing tang retention slots and shorten the bolts a tad. However, never have done this before you don't have a cutter to machine something like a bearing tang retention slot so you tell the customer it's a bit more complex than you thought, for reasons that you couldn't possibly have worked out in advance because you take your lunch breaks in the trees and answer to the name Cheetah and add another £100 to the bill. However, even having done all this, and maybe even correctly, you've still bored the top of the cap thinner by 4mm which is probably 1/3 of its original thickness so it breaks when the engine gets up to peak rpm and the crank flies out and lands in the road. Luckily the engine stops at the same time so you don't have too far to walk back and pick the crank up!
I could continue in this vein for some time but I'd only be gilding the tulip or whatever it is that us enjineers wot actually studied maths say when we're pontificating.
I see where you're coming from, the machine shop in question is two old fella's that have been doing this since people were lapping austin seven valves into blocks at the roadside.
Its certainly not ideal, but could it work in a relatively low stressed 40 year old engine? I think so.
Pumaracing said:
Huntsman said:
Yes my thoughts entirely.
I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Ummmm, maybe it's time, 20 years or otherwise, to think using about a new engineering firm with slightly smarter primates working for it! If the caps from another engine were perfectly in line laterally but a bit too large vertically because the split line wasn't in just the right place then ok. However, as the caps from another engine are absolutely certain to be more out of line laterally than they are ever going to be vertically then shaving a few thou off the faces of them won't make a rat's arse of difference to that. You'll still end up with a cap that's out of line on one side where the boring bar never touched it because, well ummm, it was out of line on that side!I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Now I could go into a vast amount of detail about the mathematics of chord theory as applied to semicircles but I'd just send everyone in here other than university level maths graduates to sleep. However I can run the calculations because for reasons that now escape me one of the hundreds of computer programs I've written over the years to help with my race engine designing just happens to be one that solves these particular equations.
If the cap from say a 64mm diameter bore was misaligned by only 10 thou (0.25mm) laterally how much would you have to mill off the split line to bring the width of the entire cap within the bounds of the lower half of the semicircle so you could line bore it back to size and touch every part? Obviously you need to bring one side back by 0.25mm so therefore the other side will come back by the same amount so you want the chord across the base of the cap to now be 63.5mm long instead of 64mm long. With me so far?
The answer is 4mm! A non trivial amount. You've now lost a good part of the bearing tang retention slots so the bearings won't fit and the main bolts might even bottom out in their holes. Arse! So machine new bearing tang retention slots and shorten the bolts a tad. However, never have done this before you don't have a cutter to machine something like a bearing tang retention slot so you tell the customer it's a bit more complex than you thought, for reasons that you couldn't possibly have worked out in advance because you take your lunch breaks in the trees and answer to the name Cheetah and add another £100 to the bill. However, even having done all this, and maybe even correctly, you've still bored the top of the cap thinner by 4mm which is probably 1/3 of its original thickness so it breaks when the engine gets up to peak rpm and the crank flies out and lands in the road. Luckily the engine stops at the same time so you don't have too far to walk back and pick the crank up!
I could continue in this vein for some time but I'd only be gilding the tulip or whatever it is that us enjineers wot actually studied maths say when we're pontificating.
The thing is, they wouldnt even bother machining the cap down by 4mm. They would just guess how much to take off. Probably around 20 thou, after line boring and realising the cap isnt fully cleaned up it would then get put on the line hone and that one cap would keep getting removed and slightly machined down until they were happy with the result. This result will probably be half an inch of untouched cap at one side. This will then be sent out to the customer as being servicable, after of course they've rubbed said offending area with wet and dry to hide it as much as possible!
Having worked in an engine remanufacturers for a few years i can honestly say that generally they really are a bodging bunch of neanderthals with little or no engineering or mathmatical knowledge. Ofcourse there will be a few exceptions to this rule!
I had to leave as my ideas of trying to do jobs properly didnt sit well with the foreman, and the idea of basically being an unskilled worker (which is how i view many in this trade) didnt sit well with me!
Huntsman said:
Its a 1965 Ford Windsor V8.
I see where you're coming from, the machine shop in question is two old fella's that have been doing this since people were lapping austin seven valves into blocks at the roadside.
Its certainly not ideal, but could it work in a relatively low stressed 40 year old engine?
Seriously? Do you think a bearing with a 10 thou gap round 25% of its circumference is going to generate any oil pressure?I see where you're coming from, the machine shop in question is two old fella's that have been doing this since people were lapping austin seven valves into blocks at the roadside.
Its certainly not ideal, but could it work in a relatively low stressed 40 year old engine?
Edited by Pumaracing on Thursday 21st October 20:39
Pumaracing said:
tr7v8 said:
Huntsman said:
Pumaracing said:
Line boring would sort it as long as you make sure it hasn't already been line bored at the factory. You can generally only get shells in the one oversize on the o/d.
Yes my thoughts entirely.I spoke to the engineering works I have been using for 20 years about it.
They said they could shave a few thou from the mating face of the caps to make the hole smaller, then line bore, so std size OD shells would fit. It would add £180 to the cost of the rebore and facing off work.
Not sure if oversize OD shells are available for this motor.
I reckon as it is the block has very little value.
Edited by tr7v8 on Saturday 23 October 20:58
tr7v8 said:
Dave I understand a lot of your comments & respect them but con-rods on diesels with very much higher bearing loads have been recircled like this for many, many years with no problems.
You obviously haven't read what I posted properly or understood the issue. Conrods can be recircled because the cap and rod are still aligned laterally despite having stretched vertically to a small degree of ovality, usually no more than a couple of thou. Grinding a small amount off the mating faces corrects the ovality and then you can hone back to perfectly circular.You can't just bore or hone two halves of a main bearing housing back to circular at the original size if the two halves are not aligned laterally in the first place because it isn't the original cap!
Now please tell us how you'd hone that back to the O/E size when both halves are already at that full size.
Edited by Pumaracing on Sunday 24th October 14:41
GavinPearson said:
But to Pumaracing's point, there may not be shells available. I understand that some diesel conrods get honed, but they also have shells available to support them.
That isn't my point though. If shells which are o/s on the o/d are available and the lateral mismatch of the cap is less than the radius of this o/s then there's no problem as I said in my first post. My point is the engineering firm saying they can bore a mismatched cap back to the OE size by grinding a few thou off the cap and me, and maths, say they can't without milling a huge amount off the cap. O/S main shells are normally available in one size at about +0.40mm (16 thou) on the o/d so you can just about correct a lateral mismatch of up to 8 thou with careful boring.However to correct a lateral mismatch of cap to base of only 1 thou back to the "OE bearing size" requires a non trivial 1.25mm to be ground off the cap of a housing with a 64mm bore. The reason should be very obvious. At the splitline of the cap the tangent to the circle of the bore is exactly vertical so grinding material off the cap initially makes no difference to the length of the chord (diameter to start with) across the cap and so makes no difference to the mismatch. It's not until you have removed a significant amount of material that the tangent to the circle starts to slope away from the vertical and the chord across the base of the cap starts to reduce in length.
As to conrods you can always recircle those back to the OE size (only on the original cap obviously) and so o/s o/d shells are never required and are never made. At least in 30 years of doing this I've never seen any. However if you tried to refurbish a conrod on a non-original and laterally mismatched cap you'd hit exactly the same problem and it would not be possible.
The maths behind this chord theory is not complex. In the following diagram a housing of original diameter of 64mm has a cap mismatched laterally by just 0.1mm. To recircle this housing back to the OE diameter of 64mm it is necessary to grind X mm off the cap so that the mismatch disappears. The chord across the base of the cap after grinding will thus need to reduce to 64mm - (0.1 x 2) = 63.8mm
Where R is the original radius and L is half the length of the new chord the distance X (grinding amount) is given by the formula square root (R^2 - L^2)
= square root (32^2 - 31.9^2) = 2.53 mm.
Edited by Pumaracing on Sunday 24th October 14:42
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