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Heavy smoke during test on Rolling Road


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Dear all,

2 weeks ago, I had my TR4A tested on a Rolling Road. 

I learned in the article 'Tales of TS2' in the last TRAction that the car must be tuned before the test can take place. The distributor was overhauled 4 years ago by the Distibutor Doctor and then the SU HS6 carburetors were also overhauled by Burlen in England. For 500 miles the spark plugs, break points, condenser, coil with its leads and spark plugs were renewed. Also the valve clearance was adjusted. I had the camshaft replaced 5,000 miles ago and then all the other vital parts of the engine were checked and replaced if necessary (piston rings, cam followers and one valve were replaced – cilinderhead was made lead free). 

Before the test on the Rolling Road, all the points, above mentioned, were discussed, the pre-ignition was checked (8° at 850 rpm and 31° at 3,100 rpm) and the carburettors were checked (correct needles!) and tuned. 

The test went smoothly until the speed of 3,500 rpm was reached. Then suddenly a heavy plume of smoke came out of the exhaust. The attached video has been shortened showing only the phase of smoke development starting at 3,500 rpm. II've never seen this smoke development, but I always switch into overdrive when I get at 3,000 rpm. So I have nearly no experience with revolutions above 3,500 rpm.

The test was repeated up to 3 times and each time we got that sudden plume of smoke at 3,500 rpm. The speed was not increased further.

Any idea what this problem could be? Thanks for your input.

Jean-Marie

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That it occurred so repeatedly at a certain revs says 'piston ring flutter' to me.    The rings vibrate in their lands around the piston and fail to seal.   Usually accompanied by a loss of power -. Was that seen by the testers?

Simply replacing the rings with a hone of the bore walls may cure it.   But if you never see the smoke when you drive with your normal style, why bother?

Edited by john.r.davies
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Possibly as it’s never seen over 3000rpm it’s an accumulation of soot and exhaust debris ?

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The smoke looks black rather than the blue you get with continuous oil burning.   Soot or over fuelling?  Could be just the muck in the exhaust being vibrated/blown out.

Yes a good point Hamish.  Amazing what an Italian tune up will blow out the exhaust pipe.   

What if the PCV is playing silly beggars at higher crankcase pressures as experienced at over 3 k rpm.   Run a pipe overboard and bypass the PCV.  Block the inlet manifold hose from the PCV.  That would prove the function of that item.

Persons with more rolling road experience will be along soon.

Peter W

 

 

 

 

Edited by BlueTR3A-5EKT
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I think the problem is originating from the vacuum generated by the inlet manifold to the rocker cover.

I would disconnect any hoses associated with the intake manifold/air filters, block off and test again.

Also check how much air pressure there is coming out of the rocker cover fitting at the low and high rpm's.

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13 hours ago, ntc said:

Safe bet just cleared it’s lungs rr person should have known that 

Yep definitely clearing the soot out of the exhaust, Obviously needs an Italian tune up first.

Stuart.

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1. To: john.r.davies:    There was no loss of power during smoke generation. Attached are the results of the unfinished test.

2. To: Peter W. and Stuart:   What is 'an Italian tune up'?

3. To: Peter W:   Overfueling was the first reaction of the person, who performed the test. But where to look at? I cannot repeat the test without get involved in a scenario where this company will search for hours (4...8 hours was there estimate).

Thank for your help.

Jean-Marie

RollingRoadResults1.JPG

RollingRoadResults2.JPG

RollingRoadResults3.JPG

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Jean-Marie

its as a couple of us have suggested it looks like a soot type build up from the exhaust system as it appears to be a black "dry" cloud 

oil burning would appear as a more blue "smoke"

and Italian tune is a saying to describe a more robust high Revving drive to blow out all that accumulation.

this accumulation can occur in cars that rarely are driven "spiritedly"on the upper rev range

a 1/2 hour run out using the full rev range is what's needed this doesn't have to be fast  you can do this in lower gears

(it doesn't need to be flat out in 4th that would be wrong to suggest on the road..........................)

 

and you described your driving :-

II've never seen this smoke development, but I always switch into overdrive when I get at 3,000 rpm. So I have nearly no experience with revolutions above 3,500 rpm

which would fit with the symptoms.

 

the good news is- - -  its not an indication of something being wrong with the car and its an easy fix to try.

 

Edited by Hamish
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Italian tune up…   My childhood memory of when we holidayed in Italy was young lads driving Fiat 500s flat out in every gear.…drive it like you stole it and are being chased.


 

Was there no ‘sniffer’ probe in the exhaust which tells the dyno operator what the fuel to air ratio is.  Without that they have little chance of getting the carb mixture corrected.   They can set the idle mixture using simple carb piston lift method, but at running and loaded rpms they would want to know if the carbs are too rich or too lean.  Lean being a disaster as it might melt things in the combustion area.  Rich causes bore wash and the pistons have reduced lubrication, meaning faster wear.   Rolling road operator should advise you if it is too lean/rich  and either correct it or stop the test.

Edited by BlueTR3A-5EKT
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Looks like soot.

Either it's accumulated soot in the exhaust/manifolds or it is running very rich. The latter should show unburnt hydrocarbons in the exhaust probe. The former should clear with a good blast (aka Italian tune up)

Ring issues/blow by result in oil being burned which gives blue smoke.

Brake fluid gives white smoke.

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I would be concerned if my TR's engine never exceeded 3000.  It's a sports car, and should be permitted to exercise itself properly where possible.  Once the engine is warm, I try to reach at least 4500 at least once in any run, even if it's only some 10 or 12 miles.

On my way to Malvern, I was followed for quite some miles by a motorcycle.  When we got to Pershore and I had to stop in the High Street, he came alongside, complimented me on the car and said it was good to see it being exercised properly!  I won't say what speeds we had been doing!  I invited him to pull ahead as there were several vehicles in front and he would be able to press on.

Ian Cornish

Edited by ianc
Typo correction!
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Sorry, I'm late to this thread but you have described an engine where the piston rings are suffering from lack of bedding in.

The standard TR camshaft does not develop full torque until 3500 revs...which your car never achieves ? The engine needs full torque to be used and for that to coincide with a full "loading" (where the engine is working hard) condition of the engine. The piston rings need this loading to be forced out sidewards to allow them to gouge out their complimentary grooves (we are talking microns) in the walls of the liners. Excessive revs are not what helps the piston rings bed in, but driving the car at revs over 3500 in top gear (4th) with your foot hard down to the floor...continually, allowing the car to develop speed and increase the revs DOES. 

This condition is well known and described as BMEP (Brake Mean Effective Pressure) Google it and you will find it described and how it works. Briefly the engine achieves it's most compression (which thrusts out the piston rings) on it's downward power stroke when the engine is loaded (working hard) and full throttle is continually applied. This is normally about the maximum torque area of your engine (3500 revs) where your engine mostly skirts apart from maybe an occasional foray but unlikely to be under full throttle in 4th.

You could ask the rolling road to load your cars engine and then in 4th at under 3000 revs apply full throttle and keep the throttle applied until the engine achieves maybe 4500 or 5000 revs even. Before power runs and with about 200 miles on the engine this is what we do on the race cars.This avoids any possible exceeding of road speed limits.

Alternatively I often (when bedding in race engines ) drive the car onto a motorway (car taxed and MOT tested). Then when you come upon a long uphill gradient (I have one within 3 miles of me) I change the car into 4th gear at about 2500 revs and floor the throttle and keep it buried as the car accelerates through the camshaft max torque are and when about 4500 revs are achieved (naturally making sure I do not exceed road speed limits). Because motorway gradients are long and of a consistent gradient when the revs are achieved and them braking the car down in speed I can normally carry out this twice going uphill. Of course you must always keep an eye in the mirrors and also ahead to make sure your actions do not cause a danger to other road users. Then I come off at the next motorway junction and return back towards home going up the other side of the gradient and carry out the same procedure loading the engine and bedding the rings in. I normally invest maybe 1 hour carrying out the excercise. This is a lot more fun than stripping the engine and cheaper also !

Interestingly my saloon road car tows my caravan and I can definately feel a difference after a 6 week caravan holiday towing covering maybe 2000 miles. The caravan loads the engine nicely and freshens up the bore conditions removing any glazing from the bores and beds the piston rings in.

Mick Richards  

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Mickey, you are most diligent, and I agree with your method of bedding in the piston rings.    But I don't think that a motorway is required!   Any road will do, as long as traffic and the turns allow you accelerate in a higher gear than normal to achieve that maximum pressure in the bores.   The speed and gear should be chosen to just avoid 'bogging down', and should be followed by a period of slowing down again (hence the need to avoid traffic) under engine braking.   This will minimise the bore pressure and draw up oil from the crankcase to lubricate the bore walls, and prevent glazing.   

I do this with a new engine forward at least 50 and preferably 200 miles.  It's not hard, if you can avoid busy roads!

John

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Mick, a lot of expertise, no doubt about it!
But what do you advise me in my case.
1. Does 'bedding in' still make sense? The 'piston rings' were renewed 11,500 miles ago.
2. How does this relate to the smoke development I have at 3,500 rpm? Probably root build up. Do I go for the so called 'Italian tune' and then for the 'bedding In'?

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How new is the air cleaner element, which ones do you have, perhaps a picture?

Which needles and springs do you have in the carburettors, dont say correct, need to know whats in there.

Perhaps a picture of the spark plugs would help. 

John

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TR4A Air Filter.pdfJohn,

I'am in holiday in France and therefor I cannot make pictures or check things on the car, I use the information I have available on my computer and answer your questions as good as I can:

- Air cleaner: I installed 2 new oval type air filters (Yellow paper) in March 2020 (A thousand miles ago, as I have driven very little in the last year). See picture for the shape.

- Carburettors: SU HS6 completely overhauled by Burlen in England in March 2016 (12.500 miles ago). The tester on the Rolling Road checked the needles versus his catalogue and said that it was correct. I'm not sure, but it can be that he said QA type of needles for a TR4A in Europe.

- Spark Plugs: these were replaced by a TR specialist in Belgium 4,000 miles ago. I can assume he installed the right type, he cleaned these spark plugs 2 months ago instead of replacing them again.

Jean-Marie

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Hi,

Once had the same trouble on a motor cycle. Eventually with high revs the rear end of the silencer blew off together with all sorts of soot and debris. Having re-attached the original back end with pop rivets power was restored and the bike ran well.

May I suggest that a new silencer is fitted to your car before any further rolling road tests are conducted. Failing that it has to be the Italian tune up!

Good luck,

Tim

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4 hours ago, Jean-Marie Raedts said:

Mick, a lot of expertise, no doubt about it!
But what do you advise me in my case.
1. Does 'bedding in' still make sense? The 'piston rings' were renewed 11,500 miles ago.
2. How does this relate to the smoke development I have at 3,500 rpm? Probably root build up. Do I go for the so called 'Italian tune' and then for the 'bedding In'?

Hi Jean,

No matter what the mileage on your piston rings unless the car is used throughout it's rev range, and especially with a "loaded engine" where the BMEP is greatest, it's likely the piston rings have been "burnished" (polished) and the compression compromised.

Your description of engaging the overdrive when the car achieves 3000 revs will drop the revs of the engine by between 750- 900 revs and this when the engine is not loaded and the camshaft still not achieving maximum torque. When the engine reaches 3500 revs and it's maximum torque range it starts belching smoke, it's actually starting to enter this "zone" and the rings are doing their work scraping the bores and increasing compression.

If you follow the method I suggested you stand a chance the rings can be made to engage again with the liner walls and scrape the oil and accumulated carbon away. Get used to seeing smoke...maybe lots of smoke, in your rear view mirror as this action is carried out. However John in his previous post is mistaken, you can use a gradient to your advantage, driving uphill in 4th gear (I wouldn't use overdrive) increases the effort required by the engine to accelerate up the gradient and also the pressure delivered through the piston rings accelerating the bedding in process. I would not be unhappy driving the car to 4500 revs or even 5000 revs if the circumstances allowed and safety was not compromised on an off public road track.

Alternatively ask your rolling road to work with you and load the engine (just as they do by braking the rollers increasing effort to obtain a power reading) and run the engine in 4th through the revs as described above, (they'll have to open the doors and windows to clear the smoke). Hopefully you'll see the smoke diminishing with every run (make sure the temperature of the engine is closely watched, the heat will increase dramatically in the engine bay. 

Mick Richards

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Mike,

I am now on leave in France and will perform these tests afterwards. The last oil change (Penrite 20W60) and replacement of the oil filter happened on 14/11/2020, which is only 600 miles ago given the little driving through the Corona restrictions. Is it recommended to change the oil before the test or/and after the test?

Thanks to everybody for all the inputs.

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3 hours ago, Jean-Marie Raedts said:

Mike,

I am now on leave in France and will perform these tests afterwards. The last oil change (Penrite 20W60) and replacement of the oil filter happened on 14/11/2020, which is only 600 miles ago given the little driving through the Corona restrictions. Is it recommended to change the oil before the test or/and after the test?

Thanks to everybody for all the inputs.

No, leave the oil. At 600 miles it is barely used and if the BMEP running works lots of liner and piston ring detritus will be deposited into the sump, which then deserves an oil change. Have a good leave period.

Mick Richards

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