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Engine shaking when turned off

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MathieuG Avatar
MathieuG Mathieu G-s
Los Angeles, CA, USA   USA
1971 Triumph TR6 "TRX"
Alright thanks guys and thanks Vance for the advice on the plugs.

Restarted it and turned off few times this morning as i was doing couple of errands. Giving a bit of gas before shutting off seems to calm the run on. I'll just do this while i'll look for the exact issue.

Thanks again smiling smiley

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dicta dick Taylor
Downey, Callifornia, USA   USA
In reply to # 1539775 by MathieuG Hi everybody !

Just bought my 71' TR6, and i have a simple question.

I am used to classic cars and engine shaking when turned off, but with this one i kinda feel like its shaking hard, and not always ! Sometimes it's nearly not shaking, sometimes it's shaking for 5 more seconds after turning off.

Any ideas what it could be?

Not sure it's too big of a deal but i prefer know your experiences.

Thanks guys !

A friend has a '69 TR6 and the only way we could reduce the run-on was to set the idle speed to the lowest rpm possible. It would idle nicely at 750 so that's where it stays. If all else fails, slowly letting out the clutch with the tranny in gear can drag the motor to a stop.

Dick

dsixnero Avatar
dsixnero Dan Colanero
Westville, NJ, USA   USA
Bruce, I think you misunderstood the cam break in process.

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
In reply to # 1539963 by Darth V8R
In reply to # 1539915 by MathieuG
So to sum up here are my directions :

- Vacuum retard
- Ignition Timing
- RPM
- Engine mounts

Mathieu:

I would add a couple of things to check: Mixture and heat range on your plugs. Super lean mixtures will make the plugs run hot, and the hot plug can be a source of ignition after shut down. Likewise for heat range on the spark plugs. Make sure you are following the original recommendation for heat range.

Vance

+1 Also consider combustion chamber deposits can cause 'hot spots' which can cause Dieseling or run on.

brucejon Avatar
brucejon Gold Member Bruce Jones
Santa Cruz, CA, USA   USA
1962 Triumph TR3B
1963 Triumph TR3B "Tupperware TR3"
1969 Triumph Spitfire MkIII
1972 Triumph TR6
In reply to # 1540036 by dsixnero Bruce, I think you misunderstood the cam break in process.

I initial breakin was 20 minutes at 2k. For the first 500 miles, after the 20 minute initial break in, dont rev over 3k, and try to keep it over 2k. I set the idle to 2k when i need to idle it for extended periods working on something else
Maybe overkill, but couldn't hurt i figure.



62 TR3B (red), 62 TR3B project, 72 TR6, 69 Mk3 Spitfire EU setup
https://spitfiremk3.wordpress.com

dsixnero Avatar
dsixnero Dan Colanero
Westville, NJ, USA   USA
Bruce, the break-in sounds correct with an oil change, but after that, idle speed should be normal but when driving,try to stay in the sweet spot witch is 2K for first 500 miles. Just my opinion, thanks for the reply, Dan

brucejon Avatar
brucejon Gold Member Bruce Jones
Santa Cruz, CA, USA   USA
1962 Triumph TR3B
1963 Triumph TR3B "Tupperware TR3"
1969 Triumph Spitfire MkIII
1972 Triumph TR6
I was messing with getting my electronic tach conversion stable - which i solved with a diode. I had extended idle periods doing so. My builder who has a warranty on it guided me not to run below 2k for extended periods but keep it between 2 and 3k. Thus the 2k idle.



62 TR3B (red), 62 TR3B project, 72 TR6, 69 Mk3 Spitfire EU setup
https://spitfiremk3.wordpress.com

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barry s Avatar
barry s Silver Member Barry Stoll
Alexandria, VA, USA   USA
1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
I'd 1st disconnect and plug the vac retd line and see what happens. If still occurring, I'd advance the timing significantly so long as no kniocking and see if run-on continues. Retarded timing may cause elevated temperature.

brgtr3a Peter Derby
Eliot, ME, USA   USA
Back in the day, I owned a 1967 MGB which ran on at shutoff. I discovered the in-gear, foot on the brake, let the clutch out solution. Much to my surprise, it always jumped backward when I let the clutch out in second gear; so the engine was running backward!

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sebsjag Sebastian D
White Plains, NY, USA   USA
If you're also hearing a slight hissing sound when stepping on the brakes it could be a leaking vacuum servo. Replaced mine and the engine shaking stopped when shutting down, and hissing also cured, not to mentioned the improved breaking.

Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1540507 by brgtr3a Back in the day, I owned a 1967 MGB which ran on at shutoff. I discovered the in-gear, foot on the brake, let the clutch out solution. Much to my surprise, it always jumped backward when I let the clutch out in second gear; so the engine was running backward!

I doubt very much it was running backward. There would be no intake stroke in that case, as the engine would be pushing air OUT through the carb, and there would be no intake of fresh air/fuel to keep the engine running.

What I suspect was happening is that the engine was on a compression stroke when it was stopped, and the compressed air in one of the cylinders pushed the piston back down the bore, thus resulting in a 180 reverse motion of the crank before the engine stopped. That would give you a brief jolt of backwards motion as the engine came to a halt.

It is a known fact that engines have preferred positions in which they stop, due to the braking force supplied by each cylinder during the compression stroke. This is why the flywheel ring gear has high wear in a few locations - the starter always engages the ring gear in one of these preferred locations.

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

TR3driver Randall Y
Confusion, Los Angeles, USA   USA
I have seen engines run backwards, for a short time. One of my high school summer jobs was driving tractor on a corporate farm, and that tractor would often run backwards for a few seconds if I killed the ignition with the throttle open. Blew exhaust out the intake and everything.

What I believe happens is that when you kill the ignition, the engine keeps pumping combustible fuel/air mixture into the exhaust until the engine stops turning. Then it stops with one piston coming up on compression stroke and fuel/air in the cylinder that has already been heated by the compression stroke. If there is a hot spot that eventually gets it hot enough to burn, it forces the piston back down the compression stroke, turning the engine backwards. It starts sucking fuel/air back in through the exhaust valves at essentially full throttle (no throttle on the exhaust), which ignites from the combination of heat from the manifold, and heat of going through a compression cycle. So the engine continues to run backwards as a diesel (at full throttle but not very well) until the exhaust manifold is all cleaned out.

Since it wasn't my engine, I just enjoyed the show smiling smiley The best part was when it didn't diesel backwards, but instead the mixture in the exhaust manifold would ignite. Sounded like a cannon going off! Often complete with sparks and occasionally even a pretty smoke ring.



Randall
56 TR3 TS13571L Once and future daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

Uberxy Avatar
Uberxy Steve Fox
Va, Charlottesville, USA   USA
Two strokes can run backwards.



SR
73 TR6
86 930

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