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I've just taken delivery of a set of the Minispares C-AHT436 rockers (1.5 ratio). I plan to fit them on a Mk1 1275S with a standard AEG510 cam, standard 12G940 head, standard double valve springs and everything else is standard. The rockers come with a pamphlet that suggest one does a proper check for springs becoming coil bound and putting undue stress on the rocker gear. It is recommended that one use a DTI and a drill press to check that there is at least 0.085" (actually 0.100" is recommended) of free movement left after the valve is fully open.

My question is, given what I've mentioned about the spec of my motor, is this coil binding issue something I should get properly checked out or will I be at no risk whatsoever with this setup on an AEG510 cam?

Any advice will be appreciated.
Thanks

You should always check it, who knows what has been done in the past?

If the drill press idea is a bit too much to contemplate its still worth a functional check before actually running the engine...

Install the rockers, set the tappet gaps then carefully turn the engine over by hand until each valve spring is fully compressed - or approaching full compression if things seem really close.... Now check that you can slide a 100 thou feeler gauge between the spring coils.... make sure the feeler fits at full compression.

Cheers, Ian

My answer is don't fit them. You'll loose mid range and gain little at 5500 rpm. The choice of camshaft tells me that's not where you're aiming to be.

You should be OK as far as Coil Bind goes, but none the less, as Minimans has suggested, regardless of all else, you should always check.

When I've done them, I have slackened the adjusting screws off, fitted them, then adjusted one at a time, checking for coil bind as I go. 0.100" sounds like a lot of clearance and nothing wrong with that, but I'm quite happy with 0.050", I wouldn't go any less than that though.

I've also found that I've never really liked the results; loss of bottom end power and nothing worthwhile elsewhere.

Fitting 1.5 ratio rockers to a 510 cam will give pretty much the same valve lift and opening times as installing the SW5 cam. There is lots of positive feedback on forums about the SW5 being a good road cam.

With cam profiles that already have a lot of lobe lift then 1.5 rockers may well give loss of lower end power, and with not so much gain at mid an high rpm.

Thanks a lot for the replies. Sounds like the consensus is to check to ensure I'm safe rather than sorry.

I'm intrigued by the comments that suggest not much gain by fitting these. I'd be keen to know what cam you used them with. I can understand that one may lose flow velocity if the valves are opened too far but I have definitely heard of significant power improvements to be had by using these rockers with a standard 1275 S cam. (AEG510)

abri wrote: I'm intrigued by the comments that suggest not much gain by fitting these. I'd be keen to know what cam you used them with. I can understand that one may lose flow velocity if the valves are opened too far but I have definitely heard of significant power improvements to be had by using these rockers with a standard 1275 S cam. (AEG510)

Nothing to loose by trying them, despite what some of us have said, you may find the results worthwhile. You can always change back.

Vegard wrote:My answer is don't fit them.<SNIP>

As you have these already, if you don't try them and they would have been better, you will never know...


More "words of wisdom":

There are three possible outcomes:
1) They will make it worse
2) You won't be able to tell any difference
3) They will make it better...

So - You have a 2 out of 3 chance of being no worse off.

I apply this logic to any decision that I am making...

If you try them and they are worse, as Spider says, you can always take them off again.

Ian

Maybe I should also have asked, for those that have used high lift rockers and been underwhelmed by them, which cam did you use them with?

abri wrote:Maybe I should also have asked, for those that have used high lift rockers and been underwhelmed by them, which cam did you use them with?

I've tried them on a few engines, fitted with stock cams through to a 276 and with a variety of cam timings to try to get the best from them.

They did make noticeably more power with the 276, but only over 4000 RPM. I never bothered to run any back to back dyno tests though.

Also remember coconut the coils on your springs. There are types with 5 and 6 coils to look for, bearing unmanned that the 6 coil type will bind where the 5 coil type will not.

minimans wrote:You should always check it, who knows what has been done in the past?

I agree, always check such things when carrying out any mods, it can save you a lot of money! I say this because my 998HL A+ with standard rockers & cam has much less than 100 thou between the spring coils when the valves are fully open, so if I fitted higher lift rockers, it would probably lead to coil binding. This thread got me thinking, is this normal? I have 2 A+ heads that I use on the same engine & both have the same lack of clearance between the coils, the only modifications to the heads are to the chambers & ports, so can have no bearing on the amount of valve travel. The springs are 6-coil type, but it makes me wonder if the cam is actually a standard one, apart from the perfect bodyshell the reason I bought the Mini (29 years ago!) was because it was the fastest standard 998 I'd ever driven. Sorry, I'm not trying to hi-jack this thread, just illustrating why it's so important to check everything when modifying an engine.

Regards, Rich.

Hi,

trying a lot of combinations for years, I learned that I always got a problem with the valve guides caused by the side load using this C-AHT436. It might be better to keep the standard rockers and to use a SW5 or a SPVP3 or to get roller rockers. This C-AHT436 was still used by ST in the 1970ies and today it is good for competition engines being necessary to stay contemporary. BTW, my last problem was a broken rocker shaft. It broke inside the first bearing and I replaced it by a better quality one. What is more if running these rockers. Using a MK1 it might be a good idea to control the height of the head. It may have been scrubbed in it's lifetime and it is now necessary to support the rocker posts to get the right geometry.

Regards