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i am "rebiulding" a '40 super eight(356) and the oil passages look rather dirty, in all the engine was in great shape except a hydraulic lifter had ruined a lobe on the cam. so i was worried it may have been from a lack of oil. the oil passage access plugs are tight and i didn't want to force them. so my brilliant idea was to turn it over with diesel instead of oil for a while, not start, to clean it. has anyone done this? my dad says he used to idle cars with diesel to clean them a long time ago.

Doing a clean-out with diesel probably wouldn't get a severe build-up of rubbish out of the oil-ways. Then you are also left with diesel in the system, which might be a pain to clear out. There are very light flushing oils available instead that you could use.

But you could possibly also do damage to the cylinder bores / big end bearings etc if any grit has made its way into the engine. How long since the engine ran?

If you are unsure of what's going on inside then suggest that you check how much sediment and rubbish is in the sump. If there's a lot of build-up there, then the oil pickup might be blocked, and that will mean dropping the sump (oil pan) to give it a good clean.

I have cleaned the sump and everything I can get to. She ran when i took her apart. As I wouldn't be starting it,I don't think I can damage the cylinders. Just worried about oil passages to the lifters.

If it is that dirty, I suggest NOT running the engine with a solvent capable of cleaning oil passages to any great extent. The crud has to go somewhere and if a chunk is dislodged and redeposited where it blocks a smaller passage damage will occur. If you decide to go ahead then removing the pan and cleaning afterwards is a must. I'll spare you the details but a dirty V8 was given that cleaning method and what was a dirty but nicely functioning engine was quickly turned into an engine needing new bearings.

What are the other flushing oils I could use to do this?

My strong preference would be to reserve the use of flushing oils until after blockages and crud have been removed as much as possible by mechanical means. Just too much risk of sludge/crud moving around to other locations, circulating thru the bearings, etc. After that what you might consider (without turning the engine over other than a partial turn by hand) is to pressurize a container of flushing oil with compressed air and use it at all the external entries to the oil galleries that you can get at, flushing in both directions where practical. When you think you've got everything cleaned, again use a compressed air pressurized container of motor oil and feed it thru the main oil feed inlet on the block and try with the valve covers and pan removed to see if everything is now receiving oil. I realize this will be a lot more tedious than what you hoped for but I think it's the safest way and most likely to succeed.

Easy way isn't always the best way. The whole concept is suspect. Sounds like you're not rebuilding but fixing some valve train damage in the car and suspect it was caused by lack of lubrication. You want to do something so it doesn't reoccur, but aren't sure what.
First, I would think one would clean before attempting repairs, so you could check for damaged components, not after repair?
Second, a proper "rebuild" would require complete disassembly and have all cleaned, trued, checked, etc.
Third, I'm not up on 40s, so gurus chime in, but I thought these were solid not hydraulic lifters.
Fourth,to do any significant cleaning of the passages would require high pressure and flow and you only have at best the oil pump to do it and it's cranking slowly. Proper type flow won't occur at low (turnover) speed. For that reasons, they make a drill adapter down the distributor, where appropriate, to turn over newly rebuilt motors to get the oil flowing properly.
Fifth, you risk more damage by clogging the oil pump and may not get clean blocked passages anyway, no matter what fluid you use at that speed.
Simple fixes. There's always the old run a wire through the passages or blow out with an air gun, if you can get to them. Or take something like Blaster or WD 40 with a nozzle tube and spray to see if it passes through each one.
What plugs the passages is similar to the sludge that settles out in the pan, a combination of metallic fines from wear and thermally degraded oil and additives or "char". These are discrete sub micron particles that became insoluble in the oil and settle out but can stick together. The diesel fuel may soft the carbon deposits but won't touch the metallics. A diesel injector cleaner may be more appropriate but those rely on a warm, not cold, functioning motor. As old school, I prefer to soak parts in kerosene (or carb cleaner), repeat until fluid comes out clean and then inspect/clean manually. There are chlorinated materials that will easily "degrease" this but are not recommended for what you propose as they'll do too good a job and damage the seal/bearings from lack of lube. Mostly they've gone to hot aqueous type block cleaners, detergents and enzymes, now for environmental reasons as well. So to use that requires further tear down and possibly a drying oven.

Good advice, Jim, no simple solutions as you say. Chiming in: The 356s do have hydraulic lifters, and can't spin the oil pump by way of the distributor because the cam drives the pump and the pump drives the distributor.

(o{}o)

Good Morning all...Valvoline makes an engine flush that comes in one gallon containers. You drain the oil, pour in the flush and idle for 5 to 10 minutes. Drain, change filter, add new oil. I have used this flush for a number of years and had good luck. My 1998 Jeep 5.9 Grand Cherokee just came up on 239,000 miles and ran great on a 950 mile round trip from Scottsdale, Arizona to Los Angeles and San Diego and return last week. I use it at every 3,000 mile oil change and run Mobil 1, 10-30 oil. I use the same oil on my 31 Model A Ford and my 49 Packard, 'Miss Prudence'. When we purchased 'Miss Prudence' we dropped the pan, and opened up the valve train area and cleaned and flushed as best we could. The Packard had 45,000 miles on her when we purchased her and has 48,000 miles now, three years later. She seems quite happy. Ernie

Reminder: the key word about flushes is change "filter".
Alot of the earlier motors had NO oil filter, as my '49 288. Those that did had something not much better than a gravity filter treating a slip stream of the crankcase flow.
So deposits accumulate in the old motors depending how frequent oil is changed. Some of the earlier oils also had problems with parafins(wax), that caused even more sludge.
Detergent oils didn't come until awhile after the war.
It's a fascinating history to study lubrication from the guy in overalls with the big oil can to modern systems. It's a subject unto itself. It's still evolving and the experts disagree on what best. I've seen my boat trailer bearing lube systems change 360 in the last 25 years from grease to oil back to grease. i.e. nothing works well int hat service.
I did some work in oil recovery about 40 years ago, and it's changed alot but the elements remain the same, search for that magic fluid that prevents wear, mostly a figment of the marketing department imagination and snake oil salesmen talk. Also, oversaw some grease and solid lubricant manufacture, but did little there. We used lubricators quite a bit for high pressure/speed seals.