marina head on 1098 block

[mattyb]

I have pulled through various threads and have an idea of where I'm going but..........

I'm lucky enough to have been offered a complete marina 1300 (1275) from a friend - an excellent runner when laid up(but very very rusty !) - my question is how beneficial would using the the complete head and hif38 on a 1098 block ?? I'm not keen on a complete engine or engine and gearbox transplant - possible a LCB and larger bore exhaust to go with it ??

thoughts ??

[chesney]

It should be excellent with a large bore exhaust and a good carb
Go for it - don't forget those valves need sinking!

[mike.perry]

What about the c/r?

[smithskids]

I thought you had to grind a bit out of the liner wall for the inlet valve to clear the side of the cylinder bore?? if you put a 1275 head on a 1098 block.maybe my memory is playing tricks. Regards smithskids

[bmcecosse]

You check for clearance andsink the extra valves slightly IF necessary. The CR will be fine.

[chrisryder]

Just make sure you've got 7.8mm clearance between the face of the exhaust valves (inlets aren't a problem) and the face of the head. This gives sufficient room to allow the valves to lift fully (with a standard cam and rockers!).

I've got a mini 1275 head on my 1098, with a 1.5 inch carb and large bore exhaust, it runs a treat

[philthehill]

When checking for top end working clearances a good tip is to put a piece of soft plasticine on top of the piston/block, assemble the top end then carefully turn the engine over (making sure that you do not force it if it will not go) remove the head and measure the depth of the plasticine below any indentation. That depth will give you a good idea of the working clearances inside the combustion chamber. You can then work out if necessary how much you may need to remove from the block/pistons (or both) for valve pocketing purposes. I always use this method for checking working clearances when changing either a camshaft, pistons or valve rocker lever ratios i.e. from 1.0 to 1.5. Working clearances should always be checked when assembling modified engines. It is too late when it goes 'bang'

[bmcecosse]

Much simpler to just use a depth gauge....simple vernier caliper will suffice. Minor rockers are 1.21 ratio - and there is no advantage going to anything more unless for an out and out full race engine where wear/tear on the cam/followers/valve stems/guides is not a worry. The pistons are not affected - the risk is only of the exhaust valves clipping the block because the bore is smaller than on the 1275. 320 thou is the magic figure......... Risk it at 300 if you dare............