52 replies to this topic

[bmcecosse]

Forget the high lift rockers - your cam is already high lift. ALL heads start out at 2.750" thickness - your measuring is not accurate - and a 50 thou skim is hardly anything! You will do far far better to fit a 940 head - but DO check the exhaust valves won't hit the block. They WILL need to be recessed by approx 40 thou - maybe slightly more. Measure first!

[giz]

that measurement included gaskets so i wasn't far off, i'll speak to the local engine builders in the morning and see what they have in stock, failing that it's a trip to minispares tomorrow if they're open for a set of those springs.

[bmcecosse]

Which springs???

[giz]

http://minispares.co...id=33655&title=

as suggested by sprocket on the previous page

[bmcecosse]

200 lb is FAR too much. I would only fit the outers.

[giz]

it's difficult to know what to do with the conflicting suggestions

[bmcecosse]

Fit a 940 head and get some decent power! The CAM head is a complete waste of time - don't waste money on springs for it. Just my view....only based on 48 years of A series.......

Edited by bmcecosse, 01 January 2012 - 10:11 PM.

[Cooperman]

The strange thing is that it ran for a while. That indicates some sort of binding as the engine warms.
Now, I've only had that happen when new manganese-bronze valve guides were fitted. As the engine warmed one valve tightened and the result was a broken cam follower (in my case). The car started and ran perfectly until it got hot. Before fitting the valve springs the valves appeared to slide perfectly in the new Man-bronze guides. It's not easy to ream the man-bronze guides, but the valve stems can be lightly linished to remove 1/2 a thou or so just to be sure it's all OK.

[bmcecosse]

Unless of course there is no oil getting up to the rockers and the valve stems........ are the oil ways lined up ok between the head and the rocker pillar and the shaft ??

[Sprocket]

200 lb is FAR too much. I would only fit the outers.

lol

[giz]

Unless of course there is no oil getting up to the rockers and the valve stems........ are the oil ways lined up ok between the head and the rocker pillar and the shaft ??

yes
i've spoken to the local engine builder, he wants me to remove the head and take it down to him so he can have a look. his first thought was coil bound springs and said he may have to groove the head where the springs sit before fitting new springs to allow for the extra lift.

[philc]

_{i was also thinking no oil? or lack of?}

[tiger99]

Grooving the head is expensive and again not the correct solution to the problem, because it will reduce the static spring pressure on the valve, and less force in the final stages of closing may result in valve bounce. If you have the correct springs, you don't need to groove the head, as they are designed for the length the valve normally is, and will be correctly loaded. But you can't have more valve lift that the valve, guide, spring and rocker geometry are all designed for, or you will get the kind of problem you are having.

As has been said, use the correct rocker ratio to suit the high lift cam, instead of messing about with machining the head. Over-ambitious attempts to increase valve lift do not necessarily improve power, and you can get better results without all the problems, with cirrectly profiled valve heads, seats and ports, amongst other things. You also need to ensure that the rocker geometry is correct, and the curved pad on the end of the rocker is correctly engaging with the valve stem throughout the travel.

You should really use the springs and rockers recommended by the supplier of the cam.

[giz]

i've taken the head to the local engine specialist, he removed one of the springs which was 2". he then gave me a new set of 1.75" springs and explained that earlier 850 and 998 heads were fitted with the smaller springs and the later were fitted with 2" springs which are already compressed more in the closed position leaving less room for higher lift.
i've put the head back on and tried just 2 of the valves so far, no.1 and no.8 exhaust valves since they travel more than the inlets, and the spring gap is now .030 - .037
i'll finish it off tomorrow and try it, if it doesn't work i've wasted £12 which includes the head set (mates rates) and if it does he's a genius and i owe him some cakes.

[Cooperman]

If the springs were coil-bound at full lift the engine would not have run to begin with. You said it started and ran for a few miles. Check the guide running clearances with the valve stems.