PRODUCT FITTING INSTRUCTIONS
CST 3029 1098 Pistons
CST3029 1098cc flat top piston range ( 0.040”, 0.060”, 0.080”, 0.100 & 68mm
This piston set can be used with both floating and press fit type applications/con rods. The only difference is that when used with the press fit con rod type, the circlips are not used. The press fit con rod uses the same diameter wrist pin as that of the floating pin type.
These pistons are manufactured from a far superior aluminium than most high performance pistons. They contain a much higher silicone content and advance heat treatments which creates a more stable piston. This dramatically reduces expansion under combustion/running conditions. Consequently lower piston to bore clearances are required. These pistons are manufactured for race use so will give correct piston to bore clearance on the relevant bore size. Suggested finished honed bore to piston clearances are as follows -
Road/fast road - 0.0015” to 0.0017” (0.0381mm to 0.0432mm)
Sports/super sports - 0.0018” to 0 0.002” (0.0457mm to 0.0508mm)
Race - 0.0022” to 0.0025” (0.0559mm to 0.0635mm)
For the 68mm pistons you need to have the bores off-set bored. There is no need to offset bore for the +0.080”, but would recommend it when going +0.100” just in case 68mm bore is envisaged after that!
1 & 3 offset towards the coolant pump by 0.025”.
2 offset towards the oil pump end by 0.025”.
4 offset towards the oil pump end by 0.015”.
This will leave a thin wall between 1 & 2 and 3 & 4 bores - approximately 0.100”/2.54mm between 1 & 2, and 0.090”/2.286mm between 3 & 4. So don't panic! This works fine with the 1275 head gasket.
IMPORTANT - Because the standard available gaskets over-hang the bore on the +0.080” and +0.100” bore sizes, make sure the piston crowns are at least 0.010” below the block face when at top dead centre. For blocks that have already been re-faced sufficiently so it is either already flush with the piston crowns at top dead centre or the pistons actually protrude from the bore – either machine the piston crowns to give the desired crown to block face clearance, or machine a chamfer on to the top edge of the piston crown. For 68mm bores it is necessary to use a 1275 head gasket. Because of manufacturing tolerances and often coolant jacket corrosion, it is necessary to plug the three coolant transfer ports in the head on the spark plug side and outside chambers. The two coolant ports in the head on the manifold side need plugging and re-drilling to suit the 1275 gasket. The corresponding ports in the block also need plugging and re-drilling. To avoid excessive piston skirt wear it is essential to chamfer the bottom edge of the bores.
Ideally, the top and second compression piston rings should be gapped to give 0.004” per 1.0” of bore diameter. i.e. for a +0.060” bore this will be 2.543” + 0.060” = 2.603” bore diameter. Ring gaps will then be 0.004” x 2.603” = 0.010”. Some ring sets come supplied with larger ring gaps, up to 0.020”. This is not a problem. The manufacturers tired of complaints for customers who damaged their engines because they didn't bother setting the ring gaps correctly. To avoid this completely they decided to increase the rings gaps. Industry leaders tests have shown that gaps in the order of up to 0.025” make no difference to performance. On engines I have dynoed with such ring gaps, post dyno compression tests and leak down tests (checked on all dynoed engines as a matter of course) showed excellent readings in both cases. The oil control rings should just be assembled to the piston as they are because the assembly is designed to work at it's compressed in-situ form. This is not measurable with the piston out of the bore.
Piston ring orientation -
Top ring – Matt light-grey moly-coated face, fit with letter/numbers facing piston top
Second ring – Slate grey coloured ring, fit with letter/numbers facing piston top
Oil Control rings – Universal, fit expander first then lower rail then upper rail.
Piston orientation - an arrow, letter 'F' or small dimple close to the piston crown should be fitted towards the coolant pump end of the block.
Ring end gaps should be fitted so there are no over-laps between the rings. Fit piston to bore with top ring end gap at rear of piston, 90 degrees to wrist pin axis. Position second ring with end gap at front of piston, 90 degrees to wrist pin axis, 180 degrees from top ring end gap. Position oil control expander ring with gap directly below 2nd ring gap, then bottom rail with end gap 120 degrees clockwise to this, and top rail gap at 120 degrees clockwise from that.