87 replies to this topic

[Cooperman]

The ex. lift of the 286 with standard rockers is 0.405". So if you measure from valve face to head surface and get less than 0.405" you'll need to recess the valve seats or pocket the block, or a combination of both. The valve can be recessed about 0.040". There is also the gasket thickness, but most like to leave that as a clearance tolerance for safety.
With a 286 it's going to be a close thing, but check it then decide what's possible.

[callyspoy]

Cheers Cooperman, confirmed that i am not a complete fool in my thinking!
I'll have a gander tomorrow then. I shall report back with my findings.

[twrminisport]

Just a thought, if you overbore a 998 +.120 with the hepolite pistons it will give you 1096cc
Might explain alot

Jesus

[liirge]

Just a thought, if you overbore a 998 +.120 with the hepolite pistons it will give you 1096cc
Might explain alot

Jesus

Hepolite pistons? you sure...

[bmcecosse]

IF it's a 1098 crank in there you MUST NOT exceed 6000 rpm therefore a 286 is not suitable. However - if it is indeed a 998 crank then much higher revs are possible and the 286 is ideal.. So - you really need to measure the stroke cally so you know exactly what's going on. And yes -i wouldn't fancy pocketing the valves by any more than 40 thou - even then - important to 'unpocket' them with a small taper nose stone.

[callyspoy]

83.5mm bore (so is a 1098)
67.5mm piston (standard Imp piston)

from deck top to top piston ring wear line (although no lip which is nice!) is 4.28mm (.168"), add valve sinking (.040) gives 0.208(5.28mm) extra clearance i can make up.

So...if my 286 cam lift is .405, and i can make space for an extra .208, i need to make sure valve top to head surface is no more than .197. On measuring, the distance is currently .252

This if my convoluted mathematics are correct, gives us .055 of clearance, EXCLUDING headgasket. So i "could" pocket down to .113 and still have the headgasket as my margin for error.

Now i'm not suggesting i will definitely go ahead with this, but can i just have someone tell me whether my calculations are correct, as i really would appreciate! Remember, the maths, not the sensibleness!
Although the sensibleness too aswell, why not eh!

[Tupers]

You could have Cometic make you a lightly thinker head gasket to gain the clearance but I'd imagine the price would out weigh the convenience.

[twrminisport]

Eurgh, Stupid moment
Hypatec not Hepolite.

/rant/ WHY CAN WE NOT EDIT POSTS /rant/

Jesus

[Tupers]

You can edit posts, the button for it's in the bottom right hand corner of each post you make.

Edited by Tupers, 08 December 2011 - 06:26 PM.

[callyspoy]

So, were my maths accurate?!

[bmcecosse]

I assume you mean 83.5 mm STROKE - making it a 1098 crank (actually should be 83.72) - so 6000 rpm rev limit, which means a 286 is NO USE for that engine since it develops power higher up the rev band where the 1098 cannot go..... you will be much better with an MG Metro cam (or 266 cam which is much the same..)- since these cams have their working range within your engine's capability.

[callyspoy]

Yes, stroke, you know me Roy, i get confuddled, ha!
I was thinking 266, might just sell the cam, followers and duplex (it's the "lighter" one)
Am thinking of getting a vernier belt drive, i know it's not really your thing, but i just fancy it!
Hmm...

[bmcecosse]

I sold the belt drive I had - don't do it! Duplex is great.

[callyspoy]

Ha, think we had this debate when i wanted to fit one to my Morris!

[bmcecosse]

Indeed........