This thread is fascinating and super informative!!!! Thanks to all those contributing!!!!! As a C4 operator I’m learning new things about keeping my engine in top form.
1. As an M18 owner I can tell you that in normal automatic shifting operation of the DTD Hydramatic transmission in an R975 C4 engined vehicle is fairly kind to the engine crankshaft. The shifts are smooth going up. Clutch operation in a manual shift set up with a R975 C4 will, as suggested, stress the crankshaft bolts a lot.. BUT, and this is a big one, if you downshift an M18 going to a lower gear from high speed to that lower gear you will get a head-jarring ‘bang’ as the engine rpm is increased by the transmission gear change. There is actually a noticeable ‘bang’ sound when that is done too. I suspect the downshifting may be the source of shock and ultimate failure of the crankshaft bolts in C4 engines in M18s. Normally one would expect an automatic transmission to be ‘kinder’ to the engine crankshaft but my observation as an owner is that the downshift causes a shock just about like the clutch dumping in the manual transmissioned vehicles.
2. I will alert the M18 owners I know that the engine rpm should be kept at 1000 rpm after warmup to prevent main bearing oil starvation and premature wear and engine damage. Almost everyone idles them at 600-800 rpm, not 1,000 rpm.
3. BOB: Was that C4 that you were “sorry got away from you” the core in 2007 or 2008 that I brought from you?
4. Also, anyone see any issue with using AV gas in a lower compression C4 built with the lower compression tank pistons? I know that higher octane gasoline is reputedly for detonation reduction but it seems to have other benefits. We use AV gas exclusively because one, ethanol in MOGas damages fuel pump rubber diaphragms and will cause corrosion from separation in time. Also, we have noticed ‘smoother’ operation in the R975 and super quick starts even when the engine is below 0 C. Also, using AV gas instead of MOGas has the key side benefit that the fuel in the fuel tanks does not ‘rot’ by evaporation and polymerization into the orange garbage old MOGas becomes after sitting 6 months. M18s do sit quite a while between gigs and regular operations though we try to start and run the engine to warm up temps every few months at a minimum to keep the seals in good condition.
5. Further, since it's an AC engine we ignore the M18 Lube Chart for the M18 specifying 30 wgt motor oil (vehicle type) and use AeroShell 100 aircraft engine oil for the higher cylinder head temps found in aircraft engines run in tanks.
daninnm
