Corvair DiagramCorvair Photo
Corvair Center
home forum corvairs calendar links Corvair Podcast
California Corvairs
Clarks Corvair
Clarks Corvair
“CORSA"



Chevy Corvair License Plate
Chevy Corvair Chrome Wheel
Corvair Center Forum :  Corvair Center Phorum The fastest message board... ever.
Corvair Center 
Pages: 12Next
Current Page: 1 of 2
Engine cylinders- new or used - which would you choose?
Posted by: Tom Rahochik ()
Date: October 15, 2020 12:08PM

I am now starting into my engine rebuild for my 1966 Corsa turbo. I have elected to go with +20 over sealed power forged pistons from Clarks. I am undecided at this point to have my used cylinders bored the 20 over or purchase Clarks new
cylinders in the standard size and have them bored 20 over. Brett, the machinist at the Ranch said he is uncomfortable with the standard bore of Clarks new cylinders. He believes the standard measurements are not accurate and has been in touch with Clarks regarding this issue. Once bored to 20 over, however, I would think they would be fine. Looking to choose the better for durability and cooling. All opinions are appreciated......

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: jjohnsonjo ()
Date: October 15, 2020 01:18PM

I used Clarks .040 over bored used jugs and sealed power pistons. The jugs looked like new when I got them and I checked them for size and roundness. I went with .0015 TOTAL clearance after talking with the manufacturer. That was three years and thousands of miles ago If you get factory boxes with those pistons it will say .001 skirt at the mark on the side of the pistons.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Caraholic4life ()
Date: October 15, 2020 02:55PM

In my personal opinion the stock OE GM cylinder that the Corvair had in it from the factory should work in our vehicles as designed.
When rebuilding an engine I feel that the Forged Pistons offer a better sense of reliability than the stock Cast versions.

With that said, and after fifty plus years of service, most OE cylinders that have seen 50K miles of service or more, are probably out of specifications acceptable to retain the standard size piston.

I would suggest going with an oversize piston and have the cylinders bored out by a qualified competent individual/business to meet the needs of the replacement piston being installed.

One thing I would personally advise against would be going straight from a standard size piston to the largest oversize available. I have several personal reasons for saying this but will leave it at that since it is my preference.

While an aftermarket cylinder designed for our vehicles may offer better cooling, I doubt it is necessary or would be of much benefit unless the vehicle will be driven hard on a reguar basis such as competitive applications.

This is simply my personal "Two Cents" worth of input. It is NOT a professional or official opinion based on anything other than my views.

1962 95 F.C. Van
1965 Monza Coupe
1965 Monza Convertible
Westminster, Maryland

MID ENG enthusiast &
prior Kelmark owner.

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Spectre ()
Date: October 15, 2020 05:17PM

If you buy from Clark's, buy them already bored.

David Clamp


1965 Corsa convertible - 140 4spd/3.55/AM-FM

2013 Mustang GT convertible - 5.0, 6spd auto, Procharger i-1

2003 Miata SE - 6spd manual (wife's toy)

"Victory is mine!" - SG

Norman, OK

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: jjohnsonjo ()
Date: October 15, 2020 05:44PM

Most post should have read Clarks .040" over bored GM factory jugs. I returned mine for the core value.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Lane66m ()
Date: October 15, 2020 05:44PM

I have about 30 cylinders in a bed liner for scrapping. Not putting money into them for no reason. No money for them with anyone I know of. Too heavy to ship. Most have about 60k on them.

I find stock size pistons and use Clark's full fin cylinders.

Al
Georgia

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: 66vairman ()
Date: October 15, 2020 06:07PM

Over the years there have been some good discussions about cylinders, mew and used.

Just me, but I won't more than 0.030" over with a stock cylinder. Less than that on a turbo engine.

Try a search.



Edited 1 time(s). Last edit at 10/15/2020 06:11PM by 66vairman.

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Wagon Master ()
Date: October 15, 2020 06:49PM

Lane66m Wrote:
-------------------------------------------------------
I find stock size pistons and use Clark's full fin cylinders.

Al, you use stock size pistons but not stock pistons, right?

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Lane66m ()
Date: October 15, 2020 07:00PM

Forged pistons and full fin cylinders for big valve 110 engine.

Rework of 110 engine in More Door got cast with NOS cylinders. Those cylinders were on hand with first intentions to use on big valve engine.

Al
Georgia

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: REM654DPG ()
Date: October 16, 2020 12:41AM

I would use the good old GM cylinders if you're only going .020 over. Just make sure the head and base gasket surfaces and fins are in good condition.

I would disagree with using the Clarks as is though and if you do go that route buy them std and have a competent machine shop hone them. My experience with the Clarks is they come too large and you end up with .004 to .005 clearance with taper and that's just not acceptable. They are nice cylinders though.

We just pulled a .060 over set of stock cylinders off of DT Cartwrights FI engine that has been running for 20 years. All of them had good compression, the cylinders are still round and straight and the forged pistons are all good too but it was time to freshen things up. They were originally torque plate honed but it goes to show that even at .060 there are no long term issues at least with an N/A engine.

Regan Metcalf
Portland, OR

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Wagon Master ()
Date: October 16, 2020 06:09AM

REM654DPG Wrote:
-------------------------------------------------------
My experience with the Clarks is they come too large and you end up with .004 to .005 clearance with taper and that's just not acceptable.


Have you told Clark's about this?
What was their response?

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: JimBrandberg ()
Date: October 16, 2020 06:30AM

I've taken apart engines that others have built with pre-bored cylinders and they were too tight, grooves on the skirts and in the cylinders. My local guy made a fixture for boring them torqued down. He's so busy that it's a long wait so I always get them in first thing when doing an engine.

I takes a pretty good cylinder to clean up at .020 so I just do .030 a lot. There's no need to plan for a second time of boring someday in my view.

Jim Brandberg
Isanti, MN
CorvairRepair.com



Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Lane66m ()
Date: October 16, 2020 06:38AM

Originally, my intent was to do low cost investment in the engine of the More Door and make a 10k reliable motor. I took a bunch of used cylinders to the local machinist to see if I could use them for the More Door engine rework. All were 0.005 oversize. That would have meant a smoking engine with standard rings. So in the scrap metal bed liner bin they went.

If I needed to buy cylinders, I decided I might as well use the NOS ones I had and get 6 new cast pistons to go with them. I had local machinist install the pistons on existing rods. New rod bearings and the lower end was ready. Crank was in great shape. Now I have an engine that is more reliable and more power than just changing 3 cylinders, pistons, rings and bearings.

Al
Georgia

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: jjohnsonjo ()
Date: October 16, 2020 07:34AM

I used the Clarks machining rather than a local shop, mainly because most of the local shops are loooooong gone. Clarks is set up to do Vair jugs. The price with your core is $31.55, $45 for good cores. Like I said before they looked NOS when they arrived. They won't give you squat for jugs if you just try to sell them. I had one with a broken fin that they wouldn't take. but got a free replacement from a friend to make a complete set. I sent them a pic of the bad one prior to shipping to save the cost of shipping a no go.

Al, where I'm going with this there is bound to be other folks in a similar situation. You are in a position to help make a complete set for these folks. Just ship one or two to Clarks with the customers order number. The need good gasket surfaces rust free inside. So if you have good ones keep them in a safe environment.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Lane66m ()
Date: October 16, 2020 08:27AM

I have honed ones the machine shop did, but they are now outside covered up in the bed liner. No room in my container.

Al
Georgia

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: jjohnsonjo ()
Date: October 16, 2020 08:33AM

Store'm in a 5 gallon bucket of drain oil, HEH

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: v8vair ()
Date: October 16, 2020 09:07AM

Some of the stock cylinders when torqued in a proper fixture do move around a bit. I found the New Full fin cylinders didnt change at all.
My current race motor is .020 stock cylinders and i have had no issues

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: jamesolefjensen ()
Date: October 16, 2020 12:17PM

When I rebuilt my 140, I had Mel at Vairmart bored out the stock (and nominal) cylinders to .020 over. He also assembled Sealed Power forged pistons on the rods and stuffed the jugs for me.

So far so good after 20K miles of mixed driving.

James
65 Corsa
SF Bay Area

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: Wagon Master ()
Date: October 16, 2020 02:46PM

jjohnsonjo Wrote:
-------------------------------------------------------
I went with .0015 TOTAL clearance after talking with the manufacturer. If you get factory boxes with those pistons it will say .001 skirt at the mark on the side of the pistons.

Are you positive about these clearance numbers? Man, that seems awfully tight.

Options: ReplyQuote
Re: Engine cylinders- new or used - which would you choose?
Posted by: jjohnsonjo ()
Date: October 16, 2020 04:21PM

WM, I wrote about this extensively before. I spoke with engineers with their CS. Lots of folks question this spec all over the WEB. The short answer is they should be considered hyperutectic for skirt to wall clearance, They have a special skirt coating, also the cut for the oil slot allows for mild skirt flexing. The pin drilled version needs more clearance.

I cut the first oil filters in half for inspection, also poured the oil through a paint filter. No aluminum or other metal tp be found.

This does not give that clearance, but explains why it is allowed to tight.


[drivcat.com]

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Pages: 12Next
Current Page: 1 of 2


Sorry, only registered users may post in this forum.
This forum powered by Phorum.