I am installing the Otto T-20 cam in my new turbo engine. Are stock springs acceptable for this cam? Should new springs be put in or are the original springs OK to use over after inspection. Should retainers be replaced?

My engine runs fine with the stock springs and the Otto 20 cam. They are used and were checked out by the mechanic who rebuilt the heads. Unfortunately, one did break. Fortunately, the damper spring held it up and it did not crash into the pistons (though the push rod got bent).

If I had to do it over again, I would have bought new stock style springs.

James
65 Corsa
SF Bay Area

Most of us use Stock Chevy 283 springs set for 100 psi

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ISKY springs are the best for bigger cams, OT 20 and Isky 270 cams push stock springs to their limits and they coil bind and break, I used to run stock springs with 280 Isky cams and they broke to often, the ISKY springs are designed for bigger cams and are way better IMO.







1960 4dr sedan caveman car
1961 Rampside (Chetside)
1962 Rampside (Barnside)
1962 Short Rampside (Shortside)
1962 Monza 700 Wagon
1963 Monza 900 coup (General Nader)

-----------------------------------
Rust Free Lancaster Ca

Dave is correct about stock spring binding with a 280 Isky cam.

The SBC springs Matt mentions have a stock tension that is only applicable to the SBC. As I learned from the shop that did my heads, the SBC spring tension at the "CORVAIR" spring height numbers will be greater vs. in a SBC engine.

Bottom line is the SBC spring has a higher tension vs. the stock Corvair spring in a Corvair engine. Just me, but I would not use a stock or SBC spring with a 280 or 270 cam.

Back to a previous thread that addressed this question.

[corvaircenter.com]

Spring selection is determined by valve lift and when you start pushing past .400 lift you are better off using a dual spring as Dave mentioned. Then, your retainer selection is determined by the springs you use. A dual spring needs a different retainer that will fit both the outer and inner spring. The two components are a matched set.

If you look on the Crower site [www.crower.com] it will show you what retainers fit the springs you are selecting and all the terminology you need to understand.

You really only need 90 to 100 lbs on the seat and 250 lbs max open or over the nose for a T-20 cam. Don’t over spring it or you’ll wear out the cam prematurely. The combo shown in the previous post worked well on a .460 lift cam up to 6500 RPM and was run on the FI engine for many many miles.

You need to find someone with a valve spring pressure gage like the ones shown in the picture. You can’t just guess work this aspect of the valve train if you want it to work well and last.

Regan Metcalf
Portland, OR

REM654DPG Wrote:

> You need to find someone with a valve spring pressure gage like the ones shown in the picture. You can’t just guess work this aspect of the valve train if you want it to work well and last.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

I use a spring pressure gauge and then use my mill quill to press the springs to a specified height to get what the seat pressure will be. You could even use a drill press with a stop on it.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

I had some springs checked at a machine shop with a high-dollar valve spring tester. Then took them home tested them in my drill press with a stop to the same height on a set of $5, garage sale, bathroom scales. And they were within 3 lb with repeatability. Good enough for me.

'29 Ford Model A Tudor (Great Grandfather bought new)
'61 700 Lakewood 110 4 speed
'69 Monza Convert. 140 Auto.
'70 Dodge Challenger R/T 440 4 speed

Been aircooled since 1973
Northwest Ohio 45840

What Isky springs are you using with an Isky 280 cam?

Jim Brandberg
Isanti, MN
CorvairRepair.com

The Isky 4005 set is what you are probably looking for along with the matching retainers and keepers. Also, check the retainer to stem seal clearance as it can bind there depending on which seals you use.

[iskycams.com]

The Isky stuff is a bit over priced and is why I use the Crower components which are as good or better quality IMOP at a much better price. What the Isky site does not tell you is whether it is a set of 12 or 16 springs and retainers. Crower only sells the springs in sets of 8 but the retainers come in sets of 12 and the keepers are in sets of 32.

[www.crower.com]

[www.crower.com]

[www.crower.com]

Regan Metcalf
Portland, OR

Man, believe me, I’m not intending to hijack a thread.

My last rebuild included an Isky 270 cam and TRW VS521 valve springs for a 65 110.

Did I do something terribly wrong?

Rockingham, NC

1962 Greenbrier
65 110 4speed

Thank you for the Crower part numbers. They are not specific about the keepers, are they 1/2 4-groove and 1/2 single groove?

Jim Brandberg
Isanti, MN
CorvairRepair.com

That Crower spring looks great, Thanks for the link Regan

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

Mike Levine

That'a a good question Jim and I kind of overlooked that detail in this thread. The isky and Crower keepers are both just the single groove and more applicable to 140s or stainless 110 size valves.

However, for most applications here you can use the GM 4 groove keepers on either of those dual spring retainers without any issues.

Regan Metcalf
Portland, OR

The Crower Specs say springs installed at 1.650 have 130# and 250 at 1.200.
if installed at 1.750 have 102# and 226 at 1.300.

Isky 280 showing .440 lift if figuring 1.5/1 rocker arm ratio.
65 Service Manual showing 1.5/1.
Otto showing 1.56/1.

I did a little testing today with a valve spring pressure tool in the drill press.
If I took a stock spring to 100# and then added another 7/16 compression the stock spring was to coil bind and 240#.
I had 3 other sets of unknown new springs. With 7/16 travel down from 100# they were in the 210-220 neighborhood. They all had an additional 1/16" or so left until coil bind.
I tried an Isky 4205. It got to 100# at 1.766 which is a little high. An additional 7/16" travel was 240# and it had an additional 3/16 or so left until coil bind. I had these when using 320HL and bigger cams for racing.
I know this is just rough comparison and I rely on Machine Shop for final fitting.

It's sort of fun to goof around with stuff but it takes a lot of time.

Is there a reason for having a single groove keeper on both 140 valves and some 4 row keepers on others?

Jim Brandberg
Isanti, MN
CorvairRepair.com

I've never seen any problem with single groove keepers but I've seen 4 groove ones that were sharp between the grooves on the valve from wear. What was the idea behind the multi groove system?

Joel
Northlake, TX
5 Ultravans, 116 Corvairs and counting...

The multi-groove lock allows the valve to rotate inside the retainer..the lock doesn't pinch the valve like a single groove lock does..allowing the valve to rotate is intended to help valve and seat life.. Ben

63 Monza coupe 4 sp (original owner)
66 Corsa coupe turbo
couple of old Vettes
Corsa member since 1978

The 86032D retainers are offset to give you about .070 or more assembled height. I like to keep a supply of both the regular and offset ones on hand so that you can tailor the assembled height and spring pressures to suit the lift and application of the specific engine.

Also, to get an accurate pressure reading on the gage with the dual spring, you need to make a spacer to fit inside the outer spring. The spacer will be the same thickness of the shoulder in the retainer (about .100) and will preload the inner spring just like when it's assembled. Not a lot of difference but still gets you the most accurate readings.


[www.crower.com]

Regan Metcalf
Portland, OR

I sort of assumed the Isky 270 was a lot like GM 891. Isky 270 Spec Sheet shows lift comparable to Isky 280 Spec Sheet. Getting close to coil bind territory with a stock spring.

Danger Will Robinson, Danger!

Jim Brandberg
Isanti, MN
CorvairRepair.com