Valve Spring Service Limit

[serviceguy]

In the last few years I accumulated 4 used heads in mainly unknown condition, 2 2Gs turbo and 2 1Gs n/t, that I proceeded and took apart. Having some time in my hands and not feeling like finishing the car in the garage due to the cold, I decided to check my inventory of spare valvetrain in order to find out what junked springs and valves I had. Assuming the valvetrain would be the same between 1G and 2G I went ahead and checked the springs against the 1G spring service limit of 47.3 mm only to find that all 2Gs were lower then that, mostly around 46.95. So I double checked on CAPS for their part number and found out that they are different, 1G being part number MD139243 and 2G part number MD185870 then checked each related FSM and found out that 1Gs have a service limit of 47.3mm while 2Gs have a 46.00 mm service limit. Does that mean the two parts are not interchangeable or the length is not really affecting the spring performance as long as found within its own serviceable dimension? And in case of the latter being true (as I believe) what can be considered a better spring between the two?

 

[BogusSVO]

I have pulled more 4g heads apart and tested the valve springs, it is a rare deal to find the stock turbo springs within spec.

Now I just junk them and replace with a aftermarket spring, such as a BC1100 w/ stock retainers. But a Manley or Crower single spring will work also.

Just checking the free height will not tell you much, except the spring is collasped.

You need to test for seat pressure at the installed height.

http://www.dsmtuners.com/forums/newbie-forum/341287-how-test-valve-springs.html

http://www.dsmtuners.com/forums/newbie-forum/341209-4g63t-valve-spring-info.html

http://www.dsmtuners.com/forums/cyl...omparison-stock-hks-bc1100.html#post152945194

http://www.dsmtuners.com/forums/cyl...2-evo-viii-stock-dsm-manley-brian-crower.html

 

[serviceguy]

Thanks for your input Bogus, I was aware of and appreciated your very informative threads on all things engine. My question was more intended to understand the difference between the 1g and 2g springs as they came from the factory, mainly because I could not find anything about any difference between the two in the most widely available literature on the subject (forums, 4g63 books etc.) but reading the FSM of both 1g and 2g the only specs that I am aware of (serviceable height limit and off-squareness) are different for the two and they do have different part numbers. I can't justify spending the money for a spring tester, I haven't even driven my 1g in two years, but I am curious about your source of the more detailed specifications on the stock springs since it seems to me like the info from the FSM is a little minimal about it (I studied mechanics and metal properties way too long ago to remember much about springs), in one of your thread you mention a catalog.

 

[BogusSVO]

The SBI Catalog, they are a parts supplier for cylinder head parts.

Some of the early 1g heads use a shorter installed height on the exhaust side only.

Since you are checking free height 47.3mm for the 1g, and 46mm for the 2g

I would have to conclude the differance is in the wire the springs are made of.

The common differance in springs is the wire dia, number of coils, and the alloy of the springs and the inch rate of the springs.

If you look at any of the aftermarket springs, none that I can think of have diffrent part numbers for 1g and 2g.

 

[serviceguy]

Thanks, it looks to me yours is the only logical explanation. I can't compare the two right now but I will when I make it back home.

 

[BogusSVO]

Ill dig thu the scrap bucket and see if I can find a few of each and test them out.

I think I may have a few stock springs laying about...

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[serviceguy]

A man's scrap is somebody else's treasure! I think I can wait another 1/2 hour before I get home to test it myself. That is if I remember to do so

 

[serviceguy]

1G spring, part number MD139243 wire diameter 3.70 mm (0.1457 inch)
2G spring, part number MD185870 wire diameter 3.80 mm (0.1496 inch)

 

[BogusSVO]

1G spring, part number MD139243 wire diameter 3.70 mm (0.1457 inch)
2G spring, part number MD185870 wire diameter 3.80 mm (0.1496 inch)

I copied this over to the spring info thread.

Thanks!