20 replies to this topic

[crn1969]

Having dismantled and cleaned head.I have lapped valves.and are all in good nick.how do I check springs? they look in good condition.or is it just good practice to install new ones? engine done 50k. Is there a way to check springs?

[Carlos W]

For the cost, I'd replace them.

 

I'm sure there are ways of measuring their torsion, but in all reality you're unlikely to have the equipment.

 

At 6000 rpm the valves are opening and closing 50 times a second, they need to be good in order to hold the valve closed

[crn1969]

Ok are they just a straight replacement or is there an upgraded set that I should go for any ideas?and from where?

[nicklouse]

you check them by measuring the free length. easy to measure but hard to find out what it should be if not standard.

[crn1969]

They are on a bog standard 998 a plus.would that info be in Haynes manual?

[gazza82]

Might be although a Metro one I have doesn't. It's in my old Autobook 2 which covers the MG Midget/ AH Sprites, so it ought to be available somewhere.

 

The Metro manual says to replace them if over 20,000 miles old!! They aren't expensive ...

 

http://www.minispare...ccessories.aspx

[crn1969]

Cheers will replace I think still would like to know the recommended length so I can check against new ones that turn up otherwise just trusting someone else to package the correct item.

[Cooperman]

Just buy a new standard set from mini Spares and they will be fine. Not expensive, but don't fit heavy duty ones because they increase the wear rate on the camshaft

[gazza82]

I could only provide a guess based on a 948cc a-series from the 50s/60s so not a 998 and not an A+ engine of about 20 years further ahead where improvements were made.

 

Minispares will be fine as Cooperman said .. I've bought a lot of parts and only had one problem .. .020 oversized shells in wrong box, so that had to be at the manufacturer, not MS!

[Spider]

A little off topic.

 

Ever seen a Valve Spring at 'work'?  It's somewhat interesting;-

 

 

While that's at a fairly high speed (8500 RPM) and not on an A Series Engine, the 'Oscillation' that occurs it somewhat of an eye opener - and very much something to be extremely mindful of when going to anything other than an OEM Spring.

 

Springs (actually, everything does, but we're talking springs here!) have a resonant frequency. Generally, the heavier the spring, the lower that Resonant Frequency will be. Multipals of the Resonant are also referred to as harmonics of it. At certain speeds / frequencies these Harmonic can have a cancelling effect and at others, they can have an adding or multiplying effect. At a particular speed / frequency a critical harmonic is reached which is usually destructive.

 

Everyone knows of the fabled wine glass shattering when rubbed with a wet finger?  999 times out of 1000 it doesn't shatter, but that one time,,,, yeap, the 'stars align' and that critical frequency is hit upon.

 

Same can happen with Valve Springs.

 

Going to heavier springs generally lowers the base resonant frequency of them, by lowering that number, it introduces many more harmonic points across an engines rev range and so increases the possibility of hitting that critical speed

 

And that can end with some real tears as it usually does very expensive engine damage.

Edited by Moke Spider, 02 February 2016 - 12:11 AM.

[OzOAP]

If its a std engine then you can maybe get away with it, but anything modified, valve springs should always be checked and measured for installed height/full lift poundage.

Some of the valve springs on the market are shocking in their inconsistency. I use this.

 

 

We also have a Spintron at work, (Youtube/Google it), Would love to get a Mini engine on it one day, to see what valve springs/pushrods are doing.

[crn1969]

Okay thanks anyone know the length the new ones should be when I get them.also I can check how much the old ones have deteriorated ?had a quick look in Haynes last night but couldn't find info.

[gazza82]

This might be worth a read .. but it doesn't seem mention all the spring lengths ..

 

https://books.google... length&f=false

[carbon]

Okay thanks anyone know the length the new ones should be when I get them.also I can check how much the old ones have deteriorated ?had a quick look in Haynes last night but couldn't find info.

 

Put all of the springs in a line, and put ruler or similar straight edge along the tops. If the uncompressed heights are all very close then for a standard 998 engine I would reuse. If there's more than a couple of mm height difference then think about replacing.

[Spider]

I have them listed with a free length of 1.95" and a rate of 79.5 lb / in.