200tdi bore wear specs

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J

jameslandy

Active Member
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128
Just going through the manual specs for the 200tdi and it states Maximum permissible overall wear is 0.177mm but then it states maximum permissible taper is 0.254mm. How is it possible to have a taper of 0.254mm when that would take the bore wear well over 0.177mm?
 
It may be that the 0.254 mm is a factory tolerance, whereas the 0.177 mm is about wear that's accumulated over the working life of the engine. In other words the first one is the tolerance they tried to work within when machining them in the engine plant. Wear tends to enlarge cylinders or make them go out of round but doesn't necessarily taper them.
 
Brown said:
It may be that the 0.254 mm is a factory tolerance, whereas the 0.177 mm is about wear that's accumulated over the working life of the engine. In other words the first one is the tolerance they tried to work within when machining them in the engine plant. Wear tends to enlarge cylinders or make them go out of round but doesn't necessarily taper them.
Click to expand...
 
Ok thanks for the reply. But we get taper from the top of bore enlarging through wear? Also why are we concerning ourselves with these measurements they give us in our manuals when surely piston to wall clearance are the important figures to measure such as 0.02-0.05mm or whatever it is i dont have the manual to hand. So if we have an overall wear largest figure of 0.08mm compared to standard bore the piston to wall is out of spec let alone 0.177 allowed?
 
I am no expert ( lets get that out of the way first):D

When measuring its left/right front/back top and bottom. you will probably find your that the bottom figures are closer together. the taper will occur between the top left/right and the btm left/right.
Reason is because on the power stroke the most force of wear is at the top on 1 side and diminish as you move done the bore, and the piston clearance (slap) will have an effect on this.

Some always say to give new pistons to a rebore company so they can bore to spec for each piston. think piston clearance as an expansion space cos you have 2 different metals;).
This is because of aftermaket differences in manufacture, where as the originals where all the same(ish).

Does that make sense cos it sure hurt my brain cell, and could be a total goose chase:D.

As for the real numbers nobody can really say without seeing all.

J
 
Yes makes total sense and the issue is not why bores wear the way they do and how to measure its the specs they give us! As u say take the piston to the machine shop and they will bore then hone to what ever the new piston manufactures state. Our manuals state 0.02-0.05mm of piston clearence well that makes the maximum allowed wear measured on an original bore 0.05mm so if you allowed 0.17mm of wear surely piston slap and rings not seating issues are a problem or do they give us that as an absolute maximum where the engine will start and run without huge emission problems and pistons slapping to the point of destruction?
 
To be honest at the moment im accepting that piston wall to bore clearence is the optimum figures to be concerned with and completely ignore the bore allowance specs they give us in the manual. Another example 200tdi vs 300tdi manual.....

200 states bores must be deglazed before renewing rings.
300 has a big warning sign saying DO NOT DEGLAZE BORES

200 rear crank seal states use some lube upon fitting 300 states DO NOT use lube as seal will leak!
 
jameslandy said:
Yes makes total sense and the issue is not why bores wear the way they do and how to measure its the specs they give us! As u say take the piston to the machine shop and they will bore then hone to what ever the new piston manufactures state. Our manuals state 0.02-0.05mm of piston clearence well that makes the maximum allowed wear measured on an original bore 0.05mm so if you allowed 0.17mm of wear surely piston slap and rings not seating issues are a problem or do they give us that as an absolute maximum where the engine will start and run without huge emission problems and pistons slapping to the point of destruction?
Click to expand...

A 200tdi will still run with bores so shagged it is unreal.
I saw one once a pro garage was rebuilding, he advertised them as rebuilt, the wear ridge was something to see and that was after he had honed it to death!
 
I remember reading that post and you mentioning that! Thats why especially these days we gotta do things ourselves
 
I had a cylinder head come back from the machine shop the other day completely out of spec I guess he wasnt banking on me measuring it. Last time i trust a machine shop.......and to be honest theres not many shops i would trust reboring and honing either
 
jameslandy said:
How is it possible to have a taper of 0.254mm when that would take the bore wear well over 0.177mm?
Click to expand...

jameslandy said:
But we get taper from the top of bore enlarging through wear? Also why are we concerning ourselves with these measurements
Click to expand...

jameslandy said:
Yes makes total sense and the issue is not why bores wear the way they do and how to measure its the specs they give us!
Click to expand...

Ok so now I am:confused:.

So lets move to specs;).

jameslandy said:
As u say take the piston to the machine shop and they will bore then hone to what ever the new piston manufactures state. Our manuals state 0.02-0.05mm of piston clearence well that makes the maximum allowed wear measured on an original bore 0.05mm so if you allowed 0.17mm of wear surely piston slap and rings not seating issues are a problem or do they give us that as an absolute maximum where the engine will start and run without huge emission problems and pistons slapping to the point of destruction?
Click to expand...

The piston clearance is for a round bore, If your tapered bore measures up within those then I would say its fine.
The piston clearance if measured in a bore shows good, then its good, regardless of bore size (given its even, not tapered)
Bore and taper are each a spec if its out of either it needs looking at, as a piston would not give a good clearance check at the taper measurements max

I am still a little confused at to what you are asking?

I would also say that it doesn't mean it wont run. but if its apart they are the measurement's to work with.

J
 
Basically im saying whats more important piston to wall or bore wear specs because it seems you cant have both in spec? Say your into your engine the cylinders look great no corrosion and you can even see the original hone marks so you mic the bore gauge and check anyway and lets say you get 0.08mm on the thrust side and 0.04 on the other so you could basically deglaze and fit new rings but where would that leave your piston to wall clearence even though your well in spec of overall wear? Lets say thats not good enough for you so you hone the taper and ovality out which will probably take you to lets say 0.14mm now your still within spec of over all wear but you now have perfectly round bores to say 0.01mm or 0.02mm if your having a bad day but where does that leave the piston specs? Way out probably? So your better honing or boring out to 20thou and fitting piston clearence to 0.02-0.05mm which is within spec on true bores.
 
Maybe 0.17mm overall wear takes into account average piston skirt wear.....maybe overall wear means overall bore and piston to bore clearance wear.
 
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