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Dashpot oil question

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TR3driver said:
Unfortunately, the local stores I checked did not carry the Blue & White; and I believe the black & white is rather thinner than 20 weight.
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I played around with different damper oils last year. The "regular" 3 in 1 is about 10 wt oil. Air tool oil is about 15 wt. Of course, the blue & white is 20 wt (and has that 3 in 1 smell, too). Air compressor oil is usually 30 wt (iso 100). And I even tried straight 50 wt. Didn't like that at all.
 
At the recommendation of the main British-car mechanic in my area (who drives a TR3 himself), my H6s use two-stroke oil, and the engine runs well at all loads and speeds. Does anyone know the weight of this oil, and has anyone else had any experience with it?
 
Roger,

Many thanks for your very helpful posting.

I have taken the 20 weight oil out of the dashpots and gone back to 30 weight. I'll try the car out today to see if this makes a difference. The dashpot springs are brand new, so I don't think that is the problem.

I had RH "rich" needles in the carbs, but I switched them out last night for SM "standard" needles, on Randall's recommendation. I'll see today if they make a difference.

I have found, using the Colortune, that my mixture is too rich. The car seems to run better when it is slightly rich, so I need to fine tune this adjustment. Your statement that "a tiny bit too rich is ideal" seems to be what I am searching for.

The problem may be the timing. I had Jeff rebuild my distributor. When he returned it to me, he included a note "12-15 degrees BTDC and w/o vacuum!" I asked him about this because all the manuals say "4 degrees BTDC" for the TR3. He answered that the formulation of today's fuel, even non-ethanol (which I use) is so different, that 12-15 degrees is what to aim for. And he added, "Update your manuals." I am currently running 4 degrees BTDC, so today I will change the timing to 12 degrees BTDC and see what happens.

In addition to the small explosions on the overrun, the car also currently tends to diesel. This is probably related to the mixture being too rich. A friend told me that another possible cause of dieseling is an idle that is too high. I lowered mine from 1000 rpms to about 800 rpms, but then the car tended to stall when stopped.

I think (hope), thanks to you, Jeff, and Randall, that I am on the right track now. Today will tell.

You are right about how these cars functioned when they were new. I had a '58 TR3 in 1962 and it gave little to no trouble.

Many, many thanks.... And Happy New Year!
 
Just to (hopefully) add a little clarity, Ed, the dashpot oil viscosity only affects what happens when you first open the throttle; it has basically no effect on steady throttle operation (eg cruise, idle, WOT, etc). And only a relatively minor effect on what happens when you open the throttle.

So my point was to leave the dashpot oil alone while you solve all the problems that are not affected by it (eg showing rich on the Colortune, backfiring on overrun, black plugs, dieseling, etc). Only then can you make any meaningful comparisons of what dashpot oil your engine "wants".

Another point, Jeff will have changed the advance curve that your distributor implements. What is important to the way the engine runs is the total advance at the moment, which is the base advance (the timing you set), plus the centrifugal advance for the current engine rpm (aka centrifugal advance curve), plus the vacuum advance for the current vacuum signal from the carburetor. So if he says to use a different initial timing, you should follow his advice.

The AMSOIL specs for their "Interceptor" 2-cycle oil would seem to put it in the range for 20 weight (8.5 cSt @ 100C; SAE range is 5.6 - 9.3). The 2-cycle oil I use as upper cylinder lubricant seems to be about 20 weight as well, but that's just based on pouring it into bottles, I haven't tried to actually measure or compare it to "real" 20 weight.
 
Randall,,

You are making it all clearer and clearer for me. Many thanks.

Jeff didn't tell me that he had changed the advance curve that my distributor implements, although I assumed he did "something" because of his laconic message to me: "12-15 degrees BTDC w/o vacuum!" When I asked him about this, he said that it was because the chemical formulation of modern fuels is different. I thought that I had advanced the timing to 10 or 11 degrees BTDC a few days ago, but apparently I missed the mark.

But today, I nailed it. I advanced the timing to 12 degrees TDC, found with the Colortune that my front carb was running lean and my back carb was running rich (I balanced them using the Colortune); changed to oil in dashpot back to 30 weight, where it had been for about a year before I changed it to 20 weight; rebalanced the carbs; reset the idle to 800-900 rpms; and -- for good measure -- put 4 ounces of Marvel Mystery Oil in a full tank of (non-ethanol) gas. Then I took a 50 mile ride up north of here and back. When I got home, I had a "new" car! So far, at least, that is the case. All systems working well and... important to me .. no more dieseling!

Thanks to all of you for helping me along the way to get this puppy running well again. A great New Year's gift, if not a true "accomplishment" by me.

Happy New Year to all... and to all a good ride.
 
OK, I've been following this thread awhile...finally have a question...

I am wondering what the reactions are to the dashpot oil. In other words, how does a car with too thin, or to thick, an oil behave?

My car needs one click of choke to get moving from a dead stop when the engine is fully warmed and the temp is 190degrees. If I push the choke all the way in, it will pop through the intake...obviously lean...during a quick start. Once rolling the car runs great, whether the choke is in or out. So, is this a sign of too thin dashpot oil? Or, is it a lean condition in general?

Of interest, if I get stuck in traffic and the engine temp gets over 200 degrees, it does not need any choke to start rolling quickly without the intake backfire.

These SU's are new to me...quite a bit different from my old double pumpers!

John
 
In general, too thin an oil will cause the piston to rise too quickly on acceleration and cause a "lean on acceleration" problem. Could cause stumbling. Too thick an oil will give good acceleration initially, but won't open up enough to give the air needed for acceleration. So it may feel like it bogs down. And we're talking the seconds on acceleration here.

It's a problem that tries to match timing the extra gas needed of acceleration with the additional air required to get the engine going. I like the 20 wt myself.
 
Pretty much the way TR3driver described it in the first paragraph of his last post.
Read it again, John.
It's a damper fluid and does not regulate the distance the air valve travels, only the speed at which it gets there.
 
Brent,

Your explanation is very helpful. I had tried both versions of the 3-in-1 oil in my dashpots to see what would happen, and I experienced stumbling on acceleration. With 30 weight oil, as you point out, initial acceleration is good but doesn't hold up. Since I try not to drive over 45 mph in this car and I get up to speed slowly, I guess I noticed the light oil effect on start-up but did not notice the thick oil effect at higher speeds. For my kind of driving, all other things being equal (that is, all other things working well) 30 weight oil seems like a good choice.
 
I agree with the answer that too thin of oil will cause stumbling on acceleration from a lean mixture. Too thick will slow acceleration (or at least throttle response) as the pistons may not rise fast enough for the rapid increase in air needed.

I have tried the Moss damper oil, and various weights and grades of motor oil from 5w-30 to 20w-50 (as well as straight 30 weight). To be honest I really couldn't tell any difference (as Randall pointed out, you usually don't have a dashpot oil problem unless it runs out. I am sure 20w-50 is probably too thick and I don't use it anymore, but if you have a modern car that uses a thinner multi-viscosity oil it will work fine, I really don't think you need to go out and buy a special oil for your dashpots (though I have certainly done it myself) but it is a (admittedly small) waste of money in my opinion.

When I was a kid I thought I'd tune my car for rapid racing level throttle response and filled the dashpots with WD40, that didn't work at all well, and I got stumbling on acceleration, but any and all middle to middle low viscosity oils tried have worked fine, I am sure ATF works fine too, but I have never tried it, generally have not owned anything with a slushbox, and now have even converted to wife to the clutch.
 
glemon,

After futzing around with various weight oils, I've settled on straight 30 weight oil. It seems to work well for me: no stumbling on acceleration as far as I can tell. Good news is that my lawn mower uses 30 weight oil, so I have a good supply for the little dashpots!
 
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