4cyl reluctant to rev, is this normal?

Tom W

Active Member
#21
Thought I’d update this, as I’ve been doing more tinkering and experimenting. I’ve swapped the 20w50 in the dashpots for ATF. This has made a big difference, both to the ability to rev, and the ease of starting from stone cold. Previously the car would turn over several times before starting from cold, now it’s much quicker with only a little choke.

The manual suggests straight SAE20 oil, which in theory the 20w50 should be when it’s cold. I think ATF is 10w, so lighter than the recommendation. Whatever, this has made the engine feel much livelier. I’ve also bought a job lot of assorted distributor springs, so I’m going to attempt to restore the original factory advance curve, then see if I can develop things from there.
 
#24
I've always used ATF or something very similar to 3in1 (which, by the way, has been around about as long as the automobile has) called turbine oil for electric motors, though for a short period I used official SU dashpot oil before I got tired of the price.

Yours
Vern
 
#25
Hello

I recently re purposed a sound Decibel meter (maybe it has a proper name) for carb tuning. You get an actual number for comparison. Just need to make sure the inlet is in the same place. Anyone else tried this? Better than the balancer that doesn’t fit right.
 

Tom W

Active Member
#26
Interesting idea, how critical is the position of the probe? I found it easy with some plumbing fittings to make an adapter for my home made manometer that works consistently.

Regarding 3in1 oil. I did look into this. There’s at least 2 types of 3in1. There’s the regular 3in1 that’s for sale everywhere. The viscosity for this isn’t specified. Then there’s 3in1 motor oil. That’s the SAE20 oil, that I suspect is what’s needed. This didn’t seem to be so readily available on the high street, or so easy to find on their website.

3in1

3in1 motor oil
 

Tom W

Active Member
#27
I’ve just looked up the data sheets for the two 3in1 oils.

The regular 3 in one has a kinematic viscosity of >7mm2/s @40deg

The motor oil has a kinematic viscosity of 68mm2/s @40deg

Clearly the SAE 20 oil is a lot thicker than the regular 3 in 1.

ATF has a kinematic viscosity of 35.55mm2/s @40deg, so not as high as the manual recommends, but not as thin as regular 3in1.

20w50 should have the same viscosity as a straight SAE20 oil at 40degrees. Whether it has the same as the SAE20 across all the temperature ranges experienced by the dashpots, I don’t know.

So the puzzle is, why do the cars run better with different (thinner) oil? Maybe they don’t? There’s lots of opinions and traditions for this, so probably you go with what you chose to believe and grab what’s to hand in the garage. The car runs well enough, so the assumption is what’s in must be right. That’s what I did with 20w50 up until now, not really considering it was too thick.

An overly thin oil should produce a lean condition under acceleration. I can’t detect any signs of running lean, but then I’m not driving everywhere foot flat to the floor all the time. Maybe the first symptom will be a burned out valve? Or maybe Rover specced things slightly on the rich side to allow for a coked up engine and a missed plug change?

I’m going to try some SAE20 oil, just to see what difference that makes.
 
#28
Tom - I think with some sort of extension hose adapter you could make it very precise as there is limited room to poke the meter in. But when angling it just the same on each side and matching the numbers if you then listen to the air flow it’s exactly right. Doing it the other way round is harder.
 
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