I own two of these as well. The first was a real "kit of parts" but it went off to a local Team Race engine tuner (Andy K) straight away. He chromed the liner and fitted his own piston. He also replaced the rod with a rectangular section replacement with 2024 alloy rather than the standard CS cheezy material. He set the timing and replaced the cylinder fin assembly with one that could be shrunk on..
It went well but the crank broke after a few races. This happened often with the CS. I don't believe it was a heat treatment problem. The crank metal just wasn't up to the job. It was replaced with one made by Steve Rothwell out of nitrated heat treated steel. I also replaced the races and fitted a Cox 09 venturi/NVA.
The engine now performs very well, however the only original bits are the crankcase the backplate and the compression screw.
A few years ago Steve Rothwell did a run of CS Tigers with his crankshaft, and a complete modified R250 top end. In tests they came within 500 rpm or so of an R250. He doesn't have any more cranks left and isn't making any more.
Within my club people are modifying the newer versions of the CS. The metallurgy seems to be much better than it was.
What they do is basically this:
Pull it apart completely and clean it. Replace any obviously faulty parts and debur the rest especially within the cylinder. Replace the races with good quality C3 races. Lighten the piston. Reassemble the motor and check the exhaust timing. Modify it to open for 140 degrees. This usually means skimming the crankcase cylinder liner face on a mandrel on a lathe. After this is right do the shaft timing to Oliver Tiger "mod" numbers. The exhaust open duration is important because it's usually all over the place on CS engines. This possibly explains why some run poorly yet occasionally one runs really well.
The new rods seem ok, but the crucial mod seems to be to fit a hardened steel disk on the backplate front face held in place with a central rivet and JB Weld. The backplate/rod clearance is then reduced to a minimum. This really works well since it seems to hold the rod big end onto the crankpin. As far as I know no engine with this mod has yet broken a rod or a crankpin.
The picture below shows a similar hardened steel disk (off an auto brake system) mounted on the backplate of a Rothwell R150, a modern copy of an Oliver Tiger Cub 1.5cc diesel. Notice the excellent finish.
After all this the CS engines seem to really perform in c/l combat models on a Taipan 8 x 4.
If you're not into fiddling with engines though it's a lot of trouble to go to for a runner. A genuine Oliver isn't all that more expensive if you're paying someone to do the work on your CS.
Another option is the Rustler range of OT replica's. They're very good, much better than any CS.