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998 Bore Clearence


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#1 gaspen

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Posted 15 September 2019 - 04:37 PM

Hello

 

I stripped down the engine because I want to rebuild it. I examined the cylinder liners and they are "glassy" as I guessed.

So the engine needs honing. Before that I measured all the liners, you'll see the result on the attachment.

 

My question is if I can use STD size pistons in this block ?

 

 

 

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#2 ACDodd

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Posted 15 September 2019 - 05:19 PM

You have just about 0.002" is wear. I would rebore that.

Ac

#3 Moke Spider

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Posted 15 September 2019 - 06:18 PM

It does have some wear in it and more than I'd accept. Since it appears you need to buy pistons, you may as well buy the oversize and have the block bored & honed to suit.



#4 gaspen

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Posted 15 September 2019 - 06:51 PM

Did you notice that all size is in "mm" instead of inch ? Just for sure  :shifty:



#5 Moke Spider

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Posted 15 September 2019 - 07:26 PM

Did you notice that all size is in "mm" instead of inch ? Just for sure  :shifty:

 

Yes.



#6 gaspen

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Posted 16 September 2019 - 01:14 PM

Next question : how and where should I measure the piston-to-bore clearence ?



#7 Moke Spider

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Posted 16 September 2019 - 07:10 PM

Most - but not all - pistons for the A Series are measured 1/2" up from the bottom of the skirt, 900 to the Gudeon Pin.

 

Check that you still have the original pistons (maybe post up a Photo).



#8 gaspen

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Posted 17 September 2019 - 09:26 AM

Most - but not all - pistons for the A Series are measured 1/2" up from the bottom of the skirt, 900 to the Gudeon Pin.

 

Check that you still have the original pistons (maybe post up a Photo).

 

I think they are the original pistons. This is an Authi Mini 1000. "FRENTE" means "FRONT" in english  :proud:

 

I measured the piston with a cheap caliper so it's not really accurate. I'll get a micrometer.

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#9 DeadSquare

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Posted 17 September 2019 - 09:44 AM

Your cheap caliper is not far out, the bore is 64.588mm.



#10 gaspen

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Posted 17 September 2019 - 08:40 PM

Most - but not all - pistons for the A Series are measured 1/2" up from the bottom of the skirt, 900 to the Gudeon Pin.

 

Check that you still have the original pistons (maybe post up a Photo).

 

I measured it : I can not insert the 0.05 mm gauge 



#11 Moke Spider

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Posted 17 September 2019 - 09:42 PM

 

Most - but not all - pistons for the A Series are measured 1/2" up from the bottom of the skirt, 900 to the Gudeon Pin.

 

Check that you still have the original pistons (maybe post up a Photo).

 

I measured it : I can not insert the 0.05 mm gauge 

 

 

Let's just back up a bit here.

 

Given that it is a worn bore and used pistons, it's fairly safe to say there's well enough piston to bore clearance here, but you'd check after having the bore honed.

I'm also wondering if you are trying to gauge if the engine needs a rebore based on these clearance numbers ?



#12 gaspen

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Posted 18 September 2019 - 06:21 AM

 

 

Most - but not all - pistons for the A Series are measured 1/2" up from the bottom of the skirt, 900 to the Gudeon Pin.

 

Check that you still have the original pistons (maybe post up a Photo).

 

I measured it : I can not insert the 0.05 mm gauge 

 

 

Let's just back up a bit here.

 

Given that it is a worn bore and used pistons, it's fairly safe to say there's well enough piston to bore clearance here, but you'd check after having the bore honed.

I'm also wondering if you are trying to gauge if the engine needs a rebore based on these clearance numbers ?

 

 

Honing is a micrometer scale process, I think it will make a very little affect on the measured numbers. First I'll will take the block to a machine shop for honing. I measure again and I'll see what to do next.

 

Haynes says that measure the bore on top and bottom. Rebore is necessary if the difference is more than 0.152mm (0.006").

 

Does Haynes mistakes ?


Edited by gaspen, 18 September 2019 - 06:43 AM.


#13 DeadSquare

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Posted 18 September 2019 - 06:42 AM

Once you get over .005" wear, there is no point in messing about;  bite the bullet and get the block rebored.



#14 gaspen

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Posted 18 September 2019 - 08:12 AM

Once you get over .005" wear, there is no point in messing about;  bite the bullet and get the block rebored.

 

Sorry I am confused  :shy:

 

The worst measure in diameter is 64.61 mm, all other dia is within this size.

 

Standard bore for 998 cc is 64.58 mm.

 

64.61 - 64.58 = 0.03 mm = 0.0012"

 

It is the quarter of 0.005"



#15 DeadSquare

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Posted 18 September 2019 - 08:23 AM

 

Once you get over .005" wear, there is no point in messing about;  bite the bullet and get the block rebored.

 

Sorry I am confused  :shy:

 

The worst measure in diameter is 64.61 mm, all other dia is within this size.

 

Standard bore for 998 cc is 64.58 mm.

 

64.61 - 64.58 = 0.03 mm = 0.0012"

 

It is the quarter of 0.005"

 

 

Sorry, my error.

 

You'll just have to wait until you have got .005" wear before considering my suggestion , Lol

 

As you say, check again after honing.






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