One for the engine gurus

[garry goodall]

Right am in the middle of stripping a head, just checking the free length of the valve springs and they was all in spec but a couple, now one measures 39.60 and another 39.58 with standard being 39.80. Would these be knackered now or would the shims need adjusting to suit?

If they are shot can I buy single springs or is a job lot change ?

Thanks on advance

 

[dac69er]

what is the tolerance of the spring free length? you say it should be 39.8, but there should be a +- either side of that.

i wouldnt worry about it tbh, its very minimal. if your stripping the head down i would re shim it anyway even if your not having any work done to it.

 

[garry goodall]

According to the manual doesn't specify any +-

Just wanna be 100% as am thinking of rebuilding it over a couple of years and forging the bottom end, so don't want any weak points lol

 

[dac69er]

0.2 of a mm is nothing mate. It won't make a difference.
If your thinking of rebuilding the head then you may as well fit new guides if needed (exhaust side is usually the worst) 're cut the valve seats and lap them all in individually. After all that you will need to reshim the valve clearances anyway.

 

[garry goodall]

Thanks mate

I've checked all of the valves and they are within spec, I'll check the guides anyway, just thought if they had shrunken they would be weaker now but if you says it's all good I won't worry about it, am new to this so there will be more posts as I strip it further lol

 

[dac69er]

the valves are hardened, the guides are a phosphor bronze I believe, so they will wear over time.

in theory springs will sag a tad and can work harden over time. if you are really worried, buy a new complete set. but I really wouldn't worry about that, valve springs are pretty resilient and rarely break. the difference you are on about is not going to make any difference. making sure the valves seal properly and getting the valve clearances right will do.

 

[bongskag]

the valves are hardened, the guides are a phosphor bronze I believe, so they will wear over time.

in theory springs will sag a tad and can work harden over time. if you are really worried, buy a new complete set. but I really wouldn't worry about that, valve springs are pretty resilient and rarely break. the difference you are on about is not going to make any difference. making sure the valves seal properly and getting the valve clearances right will do.

+1 , the only service items in a head should be valve seals and shims , I cant think of anything else you would ever need to buy a new one of ! spark plugs go without saying , and laping the valves in ..
does anyone know if it would be worth replacing the springs if re-shimming anyway ? someone must have done it , cant see any performance gain to be had tho, it would be hard to prove otherwise unless revving higher with uprated springs..