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TR2/3/3A SU-H "lift button"

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NutmegCT

NutmegCT

Great Pumpkin
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SU manuals often indicate lifting the piston 1/32" with the tip of a screwdriver, or using the lift button at the side, as an adjustment test.

If you push the lift button up fully, does that lift the piston 1/32"? or does SU mean to push that button 1/32" instead of using a screwdriver to actually lift the piston 1/32"?

Thanks.
Tom M.
 
I just lift it up (all the way I guess, never bothered with measure) with my finger then let go to test.
 
Thanks Peter. I know you can use the button to lift the piston to see if it drops correctly. I'm just wondering if the "lift the piston 1/32" and see how it changes engine speed" can be done by pushing that button all the way, or pushing that button only 1/32".

Tom M.
 
Neither, actually. If you want only 1/32", You have to lift the button a short distance before it contacts the piston and then 1/32" more.

However, the 1/32" figure was increased later on. Practical Hints & TR4 workshop both give it as 1/8", which is pretty close to what you get lifting the pin all the way. It's not super critical anyway, IMO.
 
NutmegCT said:
a-HA!

https://www.tr-register.com.au/Files/su6.html

"Check for correct mixture by gently pushing the lifting pin up about 1/32 in."

TM
Click to expand...
Sure won't work on my engine. There is at least 1/32" freeplay between the pin at rest and the piston!

I've posted links to the actual Triumph documentation many times, but its a hassle on this phone. Let me know if you need them again.
 
Thanks Randall. I've got the Practical Hints. Also good to know about the amount not being overly critical. I'm thinking now that the "use the lift pin" just eliminates sticking something under the piston; you still have to watch how far up the piston moves when you use the pin. Next time I do this, I'll actually measure how far up the piston goes, when I use the pin.

Tom M.
 
Tom, I guess the phrase is a little ambiguous "Ultimately a car with the right mixture will start easy and run well, too lean will take a long time to warm up and take throttle from cold without a miss"

A word or two changed helps: " too lean will take a long time before it warms up and takes throttle from cold without a miss"

To elaborate:

An engine that is too lean will hesitate, stall or miss with throttle applied when cold and take a long time to warm up. While such behavior is normal in subfreezing temps, if too lean the car will exhibit such behavior even on moderate to warm days.
 
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" ... too lean will take a long time to warm up and take throttle from cold without a miss".

Not sure I understand - do you mean if mixture is too lean, the cold engine revs up quickly without a miss?

Thanks.
Tom M.

 
No, just the opposite. A cold engine has to have some choke (richer mixture) to run smoothly. If the main mixture is on the lean side, then it takes longer for the engine to get hot enough that it will run smoothly without the choke.

Not necessarily a bad thing, IMO, as you'll get better fuel economy that way. But it is one indication of whether the mixture is a bit lean or a bit rich. If you can start from cold and immediately drive without the choke, then your mixture is definitely too rich.
 
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