Cylinder bore size ?

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acarlson
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Cylinder bore size ?

Unread post by acarlson » Fri May 12, 2017 12:19 pm

I am about to order new cylinders for my '65 turbo engine build. I am not building an engine to race. Should I stick with the stock bore size or go up one to +20 ? I don't necessarily need an HP increase or the heat that goes with it... Inquiring minds would like to know... Your thoughts ??

Alec
1965 Regal Red Corsa 4 Speed Turbo Convertible

66vairguy
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Re: Cylinder bore size ?

Unread post by 66vairguy » Fri May 12, 2017 1:50 pm

If you are re-using old cylinders then it's best to overbore/hone them and buy new pistons and rings to fit.

Going 0.020" over is going to make little difference in engine size.

If you are buying all new parts then pick a size that is the best price.

What ever you do - NEVER ASSUME THE CYLINDER TO PISTON CLEARANCE IS GOOD OUT OF THE BOX!!! I mic the cylinders and pistons, THEN send them to the machine shop and tell them the clearance values I expect and put them on notice I'll be verifying their work.

Many sad stories from folks with improper cylinder to piston and ring clearances that were off enough to ruin a new engine build.

You'll have a choice of cast or forged pistons. For easy driving the cast are fine. For Turbo's and lead foots the forged is preferred. Keep in mind that forged pistons (especially in air cooled engines) require nearly double the piston skirt clearance compared to a cast (stock type) piston. In the old days the TRW spec. was for EACH piston side and many assumed it was the TOTAL clearance like in the GM manual and there were a lot of scuffed pistons and poor break-in issues. There is talk that the newer forged pistons can be run at a smaller clearance - time will tell.

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acarlson
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Re: Cylinder bore size ?

Unread post by acarlson » Fri May 12, 2017 4:32 pm

I'm getting the full fin cylinder/forged piston/moly ring package from Clarks (C12861). I'm inclined to go with stock bores since, as you say, +20 isn't going to buy me much. In any case, I'll double-check the clearances.
1965 Regal Red Corsa 4 Speed Turbo Convertible

66vairguy
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Re: Cylinder bore size ?

Unread post by 66vairguy » Sat May 13, 2017 10:05 am

I have no personal experience, but the forum posts say good things about the Clark's full fin cylinders. If you order a stock bore size, then you'll have room for a bore/hone if the engine ever needs a rebuild again (unlikely).

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cnicol
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Re: Cylinder bore size ?

Unread post by cnicol » Sat May 13, 2017 7:27 pm

I'd recommend standard size too. This gives the cylinders the longest possible life. No sense in using up 1/3 of their life for no gain.
'61 140 PG Rampside
'66 Rear Alum V8 4-dr
'60 Monza PG coupe (sold, sniff, sniff)
'66 Corsa Fitch Sprint Conv. (First car 1971, recently repurchased)

Going4joe
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Re: Cylinder bore size ?

Unread post by Going4joe » Thu May 18, 2017 6:32 am

66vairguy wrote:
Fri May 12, 2017 1:50 pm
If you are re-using old cylinders then it's best to overbore/hone them and buy new pistons and rings to fit.

Going 0.020" over is going to make little difference in engine size.

If you are buying all new parts then pick a size that is the best price.

What ever you do - NEVER ASSUME THE CYLINDER TO PISTON CLEARANCE IS GOOD OUT OF THE BOX!!! I mic the cylinders and pistons, THEN send them to the machine shop and tell them the clearance values I expect and put them on notice I'll be verifying their work.

Many sad stories from folks with improper cylinder to piston and ring clearances that were off enough to ruin a new engine build.
66vairguy probably is referring to my experiences with measuring/ensuring proper cylinder to piston clearance - check my post "Help Desperately Needed" on what happened to me! Im still licking my wounds from that one and trying to rebuild my bank account before my wife divorces me for irresponsible handling of the family finanaces!

Good luck! Bill

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acarlson
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Re: Cylinder bore size ?

Unread post by acarlson » Thu May 18, 2017 7:03 am

Bill,

I did follow your saga in the "Help Desperately Needed" post and I am glad you eventually found the problem. On my rebuild I am installing all new pistons and matching cylinders. I decided to go with the stock bore. Clark's is managing the order and also balancing the rods and pistons. I will be double-checking clearances when I get the parts - I have received badly configured parts from Clarks in the past. That being said, they generally supply quality stuff... I'll let you know if something is amiss.

Alec
1965 Regal Red Corsa 4 Speed Turbo Convertible

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cnicol
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Re: Cylinder bore size ?

Unread post by cnicol » Thu May 18, 2017 7:45 am

As CORSA's Technical lead, I've been involved in several arbitrations between buyers and sellers of engine parts where the engine went south (as in self-destructed) within a couple hundred miles of overhaul.

The usual resolution: It's the engine assembler's responsibility to clean cylinders of honing residue and check all clearances. The supplier usually does not provide a second set of parts (but sometime does) and all additional labor and consequential damage is never part of the package.

Think of it this way: If you paid a mechanic to build an engine for you and the engine turned to hamburger in 300 miles, you would expect him to do the job over because it was his responsibility to do it right. When you do the work yourself, you take on that responsibility.

Bottom line: Never assume anything when building an engine!
'61 140 PG Rampside
'66 Rear Alum V8 4-dr
'60 Monza PG coupe (sold, sniff, sniff)
'66 Corsa Fitch Sprint Conv. (First car 1971, recently repurchased)

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bbodie52
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Re: Cylinder bore size ?

Unread post by bbodie52 » Thu May 18, 2017 8:25 am

:goodpost: :clap: :clap: :clap:
cnicol wrote:Never assume anything when building an engine!
Reminds me of this famous quote...

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toytron
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Re: Cylinder bore size ?

Unread post by toytron » Thu May 18, 2017 12:31 pm

So that was Oscar Wilde and not Benny Hill that said that. Lol

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