The GMC CCKW

Have started to see some drips of coolant coming from the fly wheel pan and am wondering what is the likely source. Vehicle running well otherwise .....

On the GMC 270 as on the Chev 216 there is a welsh plug in the rear face of the crankcase that can only be accessed by removal of the bell housing. They do rot out and that is the most likely source of your leak.

David

thanks David
...does that mean engine out to access it then?

The plug replacement can be done without engine removal. You will have to block up under the sump to support the rear end of engine which could be a bit awkward if yours has the extension.
First off it's floor out, gearbox out, starter motor off, clutch out, flywheel out, support engine, remove engine mounts, remove bell housing. Remove and replace plug. Reassemble in reverse order.

David

Thanks David

The rear one in my CCKW/GMC 302 rotted out a couple years ago. I pulled the engine and sent it to the machine shop to have all of them replaced. While it was there, I had them do the valves and install hardened exhaust valve seats to prevent valve seat recession from the unleaded gas.

I installed the head myself as the torque sequence on all of the GMC 302 engines is quite different.

Total cost about $900

The 302 engine from all accounts is a huge improvement on the 270. Unfortunately in this country they are quite rare.
I recall taking a 270 cylinder head to an engine shop for a refurbish and when I went to pick it up the fellow commented that they had some difficulty machining the valve seats due to their hardness. I assumed after that they must have all been made that way. I've burnt the odd valve but never had any seat trouble.
The Chevrolet built 270 engine used in the T17E1 Staghound Armoured Car was fitted with much thicker exhaust valves than the CCKW engine, presumably because they were a little prone to burning valves. I acquired a couple of sets of these for use in my truck engines.

David

"The plug replacement can be done without engine removal. You will have to block up under the sump to support the rear end of engine which could be a bit awkward if yours has the extension.
First off it's floor out, gearbox out, starter motor off, clutch out, flywheel out, support engine, remove engine mounts, remove bell housing. Remove and replace plug. Reassemble in reverse order."

David - does this mean I need to lower the back end of the engine a little to access the plug? From what I can see from underneath removing the bell housing would mean access to the plug is still at quite a steep angle .....
regards
Dave

The rear end of the engine should lower sufficiently to allow the plug to be changed. You are going to have to release the exhaust pipe and radiator hose/s but I can't think of anything else that may cause problems. Just keep your eyes open.

David

Maybe loosen the front motor mount bolts