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August 04, 2003
G'day Brad
The valve stem diameters are the same.
You can squeeze 1275cc valves into a 1098cc head (12G295) if you want to, but you will need to open the combustion chamber up quite a bit to allow gas flow around the valve, or you are defeating the purpose. Really no great advantage.
1275cc head will fit on 1098cc block, but if you have a high lift cam, and/or 1.5:1 rockers, the exhaust valves will hit the top of the block face. You will need to machine a crescent out of the block, up to .100" deep (I just did one) to allow the exhaust valves to open and to allow gas flow around them.
1098cc head will fit on 1275cc block. But you get water injection, as the water jacket in the centre of the 1098cc head opens into the bore of the 1275cc block. Not recommended.
Cylinder liners come in "A", "B", and "C" thicknesses. Sometimes even "D". An A-liner will allow you to overbore up to (say) .020". If an A-liner is already fitted, and you need to go bigger, you remove the liner and fit a B- or C-liner. Larger OD to cater for larger bore.
Liners should be stepped into the bottom of the block and therefore can't move. Not always done this way, as its easier and cheaper just to bore a hole right through. A sign of a "cheap" engine rebuild, or poor quality (read "lazy") machining.
Cylinder liners are made of much finer grade of cast iron than the original block. Our best race engines have liners fitted, whether they need them or not. The rings bed in faster and better, and the bores last longer. Power output is higher. Max output from a naturally aspirated 1330cc engine is 152 bhp at 7,500 rpm on a freshly calibrated engine dyno.
Front engine plates are different but interchangeable. The 1275cc plate has a re-inforcer across the front where the generator (or alternator) bracket mounts. Also countersunk holes for screws into the front main bearing cap, to clear the doube row timing chain.
Rear engine plates are different and not interchangeable (without suitable machining), as the oil pump cover is in a slightly different position.
I use cork gaskets front and rear on the sump, sealed with silicon (Silastic). Get it fitted correctly and you will have no leaks. The cork gasket protrudes about 3/16" above the face of the sump, and compresses into the sump as you fit it. I fit the two side gaskets to the block first, then fit the sump with cork gaskets in place up to the block. Sealer on both sides of all gaskets.
Did I miss anything?
avagoodday
Colin
PS: Gotta tell you. We just finished a 1360cc engine for a rally Bugeye. Aimed for good mid range torque, as the guy has to pull out of slow hairpins in 2nd gear - standard gearboxes only allowed in Historic Rallys and no synchro on 1st gear. We widened the camshaft lobe centres to reduce valve overlap, so we would get better low down response at the cost of top end power. With 500 rpm intervals, torque is 97 ft lbs at 3,000 rpm, then 100, 104, 105, 105, 104, 100 and 93 a 6,300. That's not a torque curve, it's a torque plateau! Max power is 119 bhp at 6,000. That's at 10.4:1 compression and running on unleaded fuel.
"Colin@SpriteParts" < colin@... > 24083
Posted on August 4, 2003 05:20 PM
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