M38 Engine Sound

Mikemc · Post by **Mikemc** » Sun Aug 12, 2018 8:53 am

You only have to try and start it once with a cylinder full of gasoline to cause a problem.

MarkR1951M38 · Post by **MarkR1951M38** » Sun Aug 12, 2018 10:27 am

Thanks but the first carb was just running rich due to vacuum leak at throttle shaft...had a little gas in manifold, but not soaked or anywhere near full in cylinder.

MarkR1951M38 · Post by **MarkR1951M38** » Wed Aug 22, 2018 2:32 pm

Well I got around to checking the bearing clearance on the rod bearings. The average was .002-.003, none over .003. Since oil pan was off and I couldn't accomplish anything, I decided to drain the oil filter (civvy fram type) and the oil smelled of gasoline. I'm thinking the first carburetor I had was so rich that the oil got diluted so much that it was not lubricating enough. The bearings on the inside next to the crank journal had minor radial scores, but for a loose engine as the L134, I'm thinking it may be ok until later when I yank the engine for a trip to a machine shop.

I put in 10W40 instead of straight 30w and as soon as a new oil filter comes in I'll get-r-started again. I will drain again and go back to 30w afterwards. 10W40 in the 70-90 degree heat of Alabama may not be so bad.

Question: When you drain oil and change filter, do you prime the oil system again using a manual pump or will the oil pump hold enough oil to get it started and build up pressure?

Ray101 · Post by **Ray101** » Wed Aug 22, 2018 3:09 pm

You shouldn't have to prime the oil sytem when you drain the oil and change the filter.

Xamon · Post by **Xamon** » Thu Aug 23, 2018 6:18 am

If there was gas in the oil I would be trying to flush everything as any residual oil will have fuel in it as well. Just my buck and a quarter (dang inflation)

MarkR1951M38 · Post by **MarkR1951M38** » Thu Aug 23, 2018 4:21 pm

Status Update: Put in 10W40 oil, cranked it up and oil pressure immediately went to 40-40+ psi with no rod knock. Drove it around the neighborhood and let it warm up to operating temp and oil pressure started to drop. At an idle the oil pressure goes to 20 psi and if I let RPM drop too much I get rod knock...so I increased the idle speed stop and rod knock went away, but pressure stays at 20 psi. Sounds good now, but low pressure.

NOTE: I purchased a new tachometer and it was faulty so I don't know the RPM. Need to check the timing too...for a future day.

With oil pressure dropping at an idle when warm tells me that the main bearings are at the limit (no, I didn't check the mains

). Wintertime project will be to remove engine and send it to a machine shop (done screwing with it). In the mean time, I'm going to drain oil once more and put back in 30 wt. and see if I can get a 30 minute drive out of it.

Thanks to all who commented/suggested.

bamaj · Post by **bamaj** » Thu Aug 23, 2018 6:45 pm

A multi viscosity oil such as 10W 40 has no actual 40 weight oil in it it's a 10 weight oil this has had additives that are supposed to make a 10 weight oil act like a 40 weight oil when it gets up to operating temperature. With our older engines it's no surprise that you would have low oil pressure running a 10 weight oil. I also live in North Alabama and with the weather we have you could almost run a straight weight oil all year around in everything you own our winters being as warm as they normally are. Advanced carries a straight 30 and 40 weight oil that is branded as Napa oil. I prefer the Rotella T oils but it would be better than running a 10 weight oil. My 2 cents

MarkR1951M38 · Post by **MarkR1951M38** » Thu Aug 23, 2018 7:12 pm

bamaj wrote:A multi viscosity oil such as 10W 40 has no actual 40 weight oil in it it's a 10 weight oil this has had additives that are supposed to make a 10 weight oil act like a 40 weight oil when it gets up to operating temperature. With our older engines it's no surprise that you would have low oil pressure running a 10 weight oil. I also live in North Alabama and with the weather we have you could almost run a straight weight oil all year around in everything you own our winters being as warm as they normally are. Advanced carries a straight 30 and 40 weight oil that is branded as Napa oil. I prefer the Rotella T oils but it would be better than running a 10 weight oil. My 2 cents

Good stuff Jeff...that's why I'm draining and going back to straight 30w from Advance Auto. Rotella is a diesel oil, isn't it?

BTW...where are you located? I'm in Huntsville. There is also another M38 guy just south of Huntsville. We need to hook up someday.

bamaj · Post by **bamaj** » Thu Aug 23, 2018 8:28 pm

It is a diesel oil but it is one of the last few oils that contains zddp which is an additive that was used after lead was removed from gas. It was introduced to help lubricate the valve train since the led was gone. Over the years with stricter spa regulations it has been removed from most all of not all of regular automotive oils. The only way I know you can still get it is either an additive or diesel oil. I haven't checked in a while but a few years ago Rotella T oil had a higher concentration than most other oils. I run it in everything I drive. I've not had a problem yet. Oh I live west of Huntsville in a little town called Town Creek over close to Muscle Shoals. I work in Huntsville every day.

MarkR1951M38 · Post by **MarkR1951M38** » Fri Aug 24, 2018 7:01 am

Thanks for that tidbit. I might try the Rotella next oil change. Is there a viscosity index on it that I'll need to be aware of?

Ray101 · Post by **Ray101** » Fri Aug 24, 2018 9:55 am

If you going to rework the engine this winter, you could run a 50wt racing oil to get a little more oil pressure when hot.

bamaj · Post by **bamaj** » Fri Aug 24, 2018 10:12 am

You can get it in a straight 30 or 40 weight oil.

MarkR1951M38 · Post by **MarkR1951M38** » Fri Aug 24, 2018 3:06 pm

Well I drained the 10w40 out of the pan and filter canister and put in straight 30w. Immediately got a steady 40 PSI. Let it run about 20 minutes to get it warmed up, temp at 180, oil pressure never below 30 PSI...and no rod knock at an idle. I'm guessing the first 30w I put in may have actually been 10w30 which would have done the same as 10w40. Need to watch the details.

Oh, did I say...NO ROD KNOCK!!! Purrs like a kitten.

Thanks for all the help guys...you ROCK!

bamaj · Post by **bamaj** » Fri Aug 24, 2018 3:27 pm

Great to hear.