It's been a while. Coming along slowly as usual...
First off I finished the intake manifold. I bead-blasted the old paint off and machined the gasket surfaces. Usually, I don't bead blast anything, but the paint was in pretty bad shape and the whole intake was full of rock-hard carbon deposits. When disassembling the heads I also noticed a lot of carbon buildup, it probably used a lot of oil when it was still running. Bead blasting was the only way to clean the insides of the intake. I also cleaned up some of the rough casting spots in the runners.
FYI: The intake manifold angle between the gasket surfaces is 88 degrees. Very odd angle, luckily we have a large milling machine that has a head that can be angled in order to fly cut the surfaces. We also have a small mill that can tilt both the head and bed (in 2 ways). Very versatile machine to have.
As I say in every post that this engine will run 99% of the time on propane
I'm implementing some tricks to get better performance on propane from the engine.
On my old 305 with its rusted heat riser (which I wired open later) the intake always got hot. With propane use, this is not satisfactory. Therefore I machined pockets in the intake exhaust gas passages in which a block-off plate will be mounted. This blocks off the stream of exhaust gas from entering the intake manifold, keeping it cooler. It is easy to remove the intake to remove the block-off plates or drill a hole in them to fine-tune the intake temperature if wanted.
Still working on the heads. I machined valve guides and reamed out the exhaust valve guides. More pictures and info on that later, however, I installed the valve guides in the first head today. They are a very light press fit and they have a shoulder so they can never fall into the combustion chamber. A positive valve stem seal can be mounted on top of the guide, which will be installed later. Now onto recutting the seats, with a 3-angle valve job.
Also modified the exhaust valve retainers to accept the Cummins valves and keepers. They are a little larger and have a slightly narrower angle. I made a simple fixture to recut them in the lathe. A little finetuning on the angle and it was spot on.
More to come, when the head work is finished I can start assembling the engine. Still have a couple of things to do such as modifying the idler gear to work with the 305 timing cover, finishing the oil filter bypass valve, and adding a ported vacuum source to the carburetor, and exhaust flanges.
I'm making a bypass valve for the oil filter because the original piece got lost in the mail. I'm making one after my own design, which should be an improvement in regards to the plunger bouching and chattering on its seat. More on that later.