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Engine Rebuilding


Best Answer Ruth's Mini , 19 November 2017 - 12:47 PM

Everyone is right above, there is some really good advice

As Moke Spider said plus 030 rebore is an odd size....can the machine shop supply pistons in that size ? or have you got them ?

 

   Strictly speaking the engineer boring the block should have the pistons in hand to be able to measure them and hone the block to the correct clearance for the specific piston and the application (road / rally / race)

Nothing worse than boring a block then finding the pistons are not available...ask Keith Calver (sorry Keith) or have been honed too too tight, then too big (customer insisting on a crap machine shop)

 

I would assume on an engine of that age to see some bearing wear... but its not common to need the line boring on the block mains ....how good was the recommendation ?...as per ACDodd and Northernpower above, they need to justify the reason to do it

 

Taking the crank to 010 is no big deal, like Moke Spider said a regrind may be a good thing as they can sort any alignment issues, which may have caused any odd bearing wear in the first place.

I would ask them to check the crank for straightness before regrinding, as being more than a few thou out can cause odd bearing wear, as Nicklouse said the bearings can tell the story.

I agree, there's really good advice in this thread especially for someone with my limited experience.

The block has been measured and I'm told 030 is where it should be bored. I do have the pistons and bearings and they will go to the machine shop for proper fit.

It was the line boring issue that had me wondering. I'll certainly have it done once they have shown me why it's necessary.

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#1 Ruth's Mini

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Posted 17 November 2017 - 03:02 PM

I'm looking for opinions on this.

 

Our engine is apart in preparation for machining and rebuild. It was running prior to disassembly but we've found main bearing wear and some cylinder wall wear. The plan is to bore the block for .30 over size pistons but the machine shop says we should also machine the crankshaft .10 under size and do a line bore. There's no damage to the crankshaft so I question the need to use anything but standard size bearings and line bore.  

 

Thoughts?

 

thanks in advance for you input...

Brian



#2 nicklouse

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Posted 17 November 2017 - 03:16 PM

without seeing (feeling) it is hard to say.

the wear pattern on the bearings tells a lot.

#3 Rorf

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Posted 17 November 2017 - 04:09 PM

Well the machine shop might have found wear on the journals - after all they would have measured them; a good machine shop would anyway.



#4 Ruth's Mini

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Posted 17 November 2017 - 05:34 PM

thanks guys

 

The other part of my question is the need to line bore. I'm displaying my ignorance here.

Does going over size on the bearings mean line boring is a must do?

 

Brian



#5 Spider

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Posted 17 November 2017 - 07:16 PM

Can we just back up here a little?

 

What size engine is it?    I ask because line boring is usually a bit of a costly process, if it's a 1275, it may just be worthwhile, if it's a small bore block, I'd suggest getting another.

 

Usually if the bearing tunnel (in the block that holds the shell) is worn, there must be a reason for it and 9 times out of 10 it will be caused by the crank having picked up on the shell for a variety of reasons, so a grind on the crank under these circumstances would usually be in order.

 

Also, having the crank ground allows you to have it indexed, that's were the Big Ends can be aligned with each other and the stock of each throw corrected, they are seldom spot on.

 

Also, regarding the suggested over bore size of 0.030", If that's what's needed then so be it, but if possible, I'd suggest going to 0.020" if it's on standard size. The only reason I suggest this is it will allow for 2 further rebores, instead of one (in the sensible over sizes).



#6 dotmatrix

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Posted 17 November 2017 - 08:54 PM

a crank can indeed look fine and still be worn past its spec'ed size and there for need machining.

I cant remember what I paid for having an 1275 a+ line bored but it was something like £80 in a machining shop.



#7 Ruth's Mini

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Posted 17 November 2017 - 11:44 PM

The car is a 1961 with the original 848 (850) engine so we want to keep it. Also being in Canada good used parts are almost non-existent so getting a replacement block isn't an option anyway. 

Price quoted by the machine shop for line boring is about 450 Canadian dollars (approximately 260 pounds).

I think machining the crank .010 under is probably advisable, just not sure the expense of line boring is necessary unless of course it must be done if the crankshaft is machined.

 

thank you all for the input,

Brian



#8 dotmatrix

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Posted 17 November 2017 - 11:57 PM

its not a must no. I bet they could check to see if it needs a line boring.



#9 Earwax

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Posted 18 November 2017 - 12:34 AM

I am just trying to get my head around this myself. Comments please ( or explanation for noob).

 

 

If wear on the shells crank side then measure crank and possible regrind crank undersize   ? Measure is achieved by micrometer on crank journals, any other measures?

 

If also wear on the cap side, then the fit with the new shells could be compromised, so line bore?   Measure achieved how / what?

 

If line bore , what is the impact /consequence of lowering the crank into the caps?

 

 

 

I add this , is it seems the OP is weighing up whether or not line bore is required,, and  if not always what are the factors that determine it?



#10 ACDodd

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Posted 18 November 2017 - 08:41 AM

The question of is it worth having a line bore is not correct from an engineering perspective. If the machine shop is trust worthy, and they have inspected the bearing tunnels and concluded a line bore is required, this is because the tunnels are oversized, Oval, tapered and or out of line, or a combination of the above. In this respect you have no choice but to do the work, if you want to be able to assemble and use the engine.

On the other hand if the machine shop is just looking for more work......

The point is, the cost is irrelevant on the need of this work if it is to make a successful build.

Ac

Edited by ACDodd, 18 November 2017 - 08:43 AM.


#11 Ruth's Mini

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Posted 18 November 2017 - 12:11 PM

the machine shop is by referral so I don't yet have a history with them...

 

great discussion, thanks



#12 Northernpower

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Posted 18 November 2017 - 12:17 PM

the machine shop is by referral so I don't yet have a history with them...
 
great discussion, thanks

I would ask them the question, what are the specific reasons it needs line boring? I would them ask them to show you on the block how they have come to the decision, this should give you confidence in them, or otherwise.

#13 Retroman

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Posted 18 November 2017 - 08:49 PM

Everyone is right above, there is some really good advice

As Moke Spider said plus 030 rebore is an odd size....can the machine shop supply pistons in that size ? or have you got them ?

 

   Strictly speaking the engineer boring the block should have the pistons in hand to be able to measure them and hone the block to the correct clearance for the specific piston and the application (road / rally / race)

Nothing worse than boring a block then finding the pistons are not available...ask Keith Calver (sorry Keith) or have been honed too too tight, then too big (customer insisting on a crap machine shop)

 

I would assume on an engine of that age to see some bearing wear... but its not common to need the line boring on the block mains ....how good was the recommendation ?...as per ACDodd and Northernpower above, they need to justify the reason to do it

 

Taking the crank to 010 is no big deal, like Moke Spider said a regrind may be a good thing as they can sort any alignment issues, which may have caused any odd bearing wear in the first place.

I would ask them to check the crank for straightness before regrinding, as being more than a few thou out can cause odd bearing wear, as Nicklouse said the bearings can tell the story.



#14 Ruth's Mini

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Posted 19 November 2017 - 12:47 PM   Best Answer

Everyone is right above, there is some really good advice

As Moke Spider said plus 030 rebore is an odd size....can the machine shop supply pistons in that size ? or have you got them ?

 

   Strictly speaking the engineer boring the block should have the pistons in hand to be able to measure them and hone the block to the correct clearance for the specific piston and the application (road / rally / race)

Nothing worse than boring a block then finding the pistons are not available...ask Keith Calver (sorry Keith) or have been honed too too tight, then too big (customer insisting on a crap machine shop)

 

I would assume on an engine of that age to see some bearing wear... but its not common to need the line boring on the block mains ....how good was the recommendation ?...as per ACDodd and Northernpower above, they need to justify the reason to do it

 

Taking the crank to 010 is no big deal, like Moke Spider said a regrind may be a good thing as they can sort any alignment issues, which may have caused any odd bearing wear in the first place.

I would ask them to check the crank for straightness before regrinding, as being more than a few thou out can cause odd bearing wear, as Nicklouse said the bearings can tell the story.

I agree, there's really good advice in this thread especially for someone with my limited experience.

The block has been measured and I'm told 030 is where it should be bored. I do have the pistons and bearings and they will go to the machine shop for proper fit.

It was the line boring issue that had me wondering. I'll certainly have it done once they have shown me why it's necessary.






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