17 replies to this topic

[skoughi]

I'm giving the MG Metro big valve head I'm using a bit of a refurb and I'm going to fit the VS2, KC 152142, double valve springs that came with the Kent 266 camshaft. Kent's website is saying that they should have an installed height of 36mm, what +/- tolerance can I play with on this setting?

[skoughi]

I've done a fair bit of searching online and have found a +/- value of 0.5mm, anyone disagree with this?

[Shooter63]

That sounds about right but if your head has the variance in spring seat depths that the one I've just done had then good luck, if the head was the norm then bmc/bl/rover or who ever had worst tolerances than harley davidson and that's saying something.

Shooter

[skoughi]

Yeah I'm starting to realise this! I threw the head on the block a couple of years ago, lapping in the valves was the most technical attention it got along with me having a go at some chamber work to reduce compression ratio was when I look at it now is rough as a dogs rear end! I'm going to cut valve seat angles along with a back cut on the valves, check valve spring height, have a go at rocker geometry, tidy up the chambers along with rechecking chamber volume and well everything is at a different height! It's going to be an interesting couple of weeks and a lot of learning ahead of me!

[skoughi]

I checked the deepest valve earlier, there's a 45 thou difference between this one and the most shallow one, and the installed spring height on that one was still too short. I suppose this gives me something to play with when cutting new seats and refacing the valve! If what you say is common then other valve springs might be completely different, better order some shims as well just in case I suppose!

[Spider]

Can I suggest another way?  I don't like what's been suggested.

 

Fit the springs up and set the tappets quite loose. Rotate the engine over by hand and check clearances between coils, you want a minimum of 0.040" but 0.050" is safer. Gradually wind up the tappets and check every time until you get to your normal setting clearance.

 

While 0.040 - 0.050" may sound like a lot, it's not. Under rapid use, the springs set up a resonance within themselves that oscillates up and down the spring. If the coils make contact while that's going on, they'll break in short time.

 

There's a high speed video somewhere, I'll see if I can find it.

[Spider]

Not actually the video I was looking for, but shows the issue well enough

 

[skoughi]

I'm thinking to make a jig that I can fit the head to that will have a threaded bar with a large flat washer that the rocker screw adjuster will sit on. I wanting the washer large enough so I can rest my dial gauge on it so I can wind it up until I get the same lift that the 266 cam will be giving. If I do this then I'll be able to check and adjust everything on the bench before it's fitted to the engine. I'll give your suggestion a go for checking the springs Moke. I'll be using the pressed steel rockers by the way.

Edited by skoughi, 23 September 2017 - 09:06 PM.

[skoughi]

Out of interest what is it that you're not liking in my earlier posts? 

[skoughi]

Those coils don't have much of a gap between them do they! So it's better to check the spring height your way rather than the way I was suggesting to avoid any risk of the coils binding?

[Spider]

Yes, by what ever means, compress the fitted spring until you get to 'normal' lift and measure between the coils.

 

The 'thing' I didn't like from your earlier posting was blanket statement from Kent, maybe it was the way it was posted, but I read it and got an impression that they say '36 mm installed height' is all that matters.

 

Also, I doubt you'd need double valves springs with a 266,,,,

[Spider]

Those coils don't have much of a gap between them do they! So it's better to check the spring height your way rather than the way I was suggesting to avoid any risk of the coils binding?

 

Fitted height is important to a degree, but yes, IMO, the gap between coils is more important.

 

<EDIT: The oscillation you see in that video occurs at ALL engine speeds, not just at high speeds, though at certain RPMs when the spring gets in to resonance, it 'amplifies'. This will occur at a few points in the rev range. >

Edited by Moke Spider, 23 September 2017 - 09:19 PM.

[Spider]

Again, not the video I was thinking of earlier, but this should highlight the importance of the detail that needs to be paid to the valve train, including the springs

 

[skoughi]

I searched Kents website and couldn't find a +/- tolerance just the 36mm. There may have been a distance between coils spec as well but at that time I hadn't been as educated as what I am now! I've actually driven her for the last year and a half on standard springs with no apparent problems. I to felt there was no need for double springs as seeing as the 266 was be touted as a "normal driving low revs torque" cam and I know that high revs means shorter engine life, plus it's my first engine build so it's not got the quality that an experienced builder can produce, remember the many messages that went back and forth between us a good while ago when I was seeking advice when I was putting the engine together? I had the intentions to take her no higher than 5k revs and have 99% stuck to that! Plus I felt that stronger springs means more wear. Anyway as I'm trying to actually have a proper go at doing the cylinder head I thought I'd fit these double springs that have been laying around doing nothing, though when I think about it then there probably is no need for them.

[Spider]

Yes mate, I remember all the messages etc.

 

Roger and I talked about behind your back when we were on our trip last year - I trust your ears were burning !  All bad things of course,,,,,

 

With Valve Springs, I fit only what's necessary, which is largely dictated by the cam.

 

I'll probably receive 'hate mail' for posting this, but it's only based on my experience. I really don't rate Kent gear at all. I've tried a fair bit of it and been disappointed in all except one time (which was actually with a 266). Not just the profiles of their cams I find disappointing, but their lack of attention to detail that will make it not only run right but last as one would expect.