What camshaft?

[roy_ston_123]

Hi all this is my first post so here goes...

I'm rebuilding my 1098cc engine e.g re bore, new crank etc. and have 12G940 head to replace orignal.
What cam would fit and improve any performance? was looking at this one on mini sport http://www.minisport.com/mini-spare-par ... D266M.html

Regards

Roy

[PSL184]

Stick with the original 1098 cam - It is a good cam and won't put any stress on the top end....

[chrisryder]

if you get a cam shaft that increases the lift, you're likely to have more problems with exhaust valve clearance with that 12G940 head.

Stick with the standard cam, the head change should give you a great improvment on its own!

[bmcecosse]

Welcome to the Forum. The standard AEA 630 cam is fine - although an MG Metro cam would be better if you can find one! That Msport cam has a bit too much lift (as mentioned already) - and it's expensive ! And I find it odd that it claims to lift the exhaust valves higher than the inlets. However - at a pinch, you could use it - just make sure you provide enough exhaust valve clearance. You certainly don't want a high revs cam - the 1098 must NOT be taken above 6000 rpm - so NO fancy strong valve springs or high lift rockers. You know about sinking the exhaust valves (I hope) - and any amount you sink the valves, must be replaced on the spring seat with a washer of that thickness.. And you MUST fit a crankshaft damper...... You will be pleased with the 940 head - if you can - do some work on the exhaust valve throats, where the gas has to turn the tight corner. Stick a finger in there and feel how little room there is for the gases - some mounted point (and NO - not with a silly Dremel!) work here on the corner and on the valve guide boss (but NOT the guide) will help the gases to escape much more easily. You also need the 1275 sintered rockers - OR (actually better) - realign the 1098 rockers on a new shaft if it's worn, so that the rockers operate DIRECTLY over each valve stem tip.

[roy_ston_123]

Thanks for the replies, i'll think i will leave the cam as it is then I did know about sinking the valves in from reading other posts on here. How do i go about re alligning the 1098 rocker? Do i just U out the holes in the posts?

[bmcecosse]

NO!!!! The rockers need to be aligned on the shaft by careful filing of the rocker body and/or the side of the pillar - and fitment of thin washers where necessary until the rockers are centered perfectly over the valve stem tips.

[roy_ston_123]

oops haha. I see what you you mean. Thanks again

[bmcecosse]

The point is -the valve centres on the 1275 heads are further apart - to allow for the larger diameter valves. This was ok with the S models because they have the special forged rockers with quite wide pads. Even there - it was/is important to modify the rockers to act directly. Later non S 1275 engines crudely used the very wide sintered rockers - which act over the valves in a very off-centre manner and cause side play to develop over time. The best rockers (apart from the expensive forged ones) are the pressed steel rockers used on the 1098 engine. These have narrow pads - and so they need to be correctly aligned over the valve stems. For extreme use (high lift cam and/or very strong springs) some folks arc weld the two halves of each rocker along the top edge. No harm doing this if you wish - but absolutely no need for any reasonable use.

[roy_ston_123]

oh yes i see now the reason behind the aligning of the rockers. Yes I have been reading David Vizrards book and he mentions about welding along the top of the rockers.