Who's had their throttle bodies modded with bearings?
Discussion
And if you have - why?
Just want to understand why people have had it done, was it due to poor running, keep going out of tune etc etc? Has it solved the problem?
I ask because i went to discuss this mod with a local vintage car restorer yesterday (they have a great reputation for this type of one-off machining, they prep vintage lemans cars, rally cars etc) and i had quite a lenghty debate over just how significant the impact of the air leakage past the bushes, or movement of the butterfly valves, could have.
For example, its been touted as a cause of high rev misfires (5k rpm +), but at full throttle (which is typically where you will be at that engine speed) is the wear affect really that significant?? Whats the mechanism causing the misfire, AFR presumaby but caused by leakage, vibration?
Im not questioning the logic of it at all, it makes perfect sense to replace the bushes, and indeed the company are happy to do the work if i want them too, and no doubt in time i will get it done, but wanted to understand the specifics of why people have done it.
Rob
Just want to understand why people have had it done, was it due to poor running, keep going out of tune etc etc? Has it solved the problem?
I ask because i went to discuss this mod with a local vintage car restorer yesterday (they have a great reputation for this type of one-off machining, they prep vintage lemans cars, rally cars etc) and i had quite a lenghty debate over just how significant the impact of the air leakage past the bushes, or movement of the butterfly valves, could have.
For example, its been touted as a cause of high rev misfires (5k rpm +), but at full throttle (which is typically where you will be at that engine speed) is the wear affect really that significant?? Whats the mechanism causing the misfire, AFR presumaby but caused by leakage, vibration?
Im not questioning the logic of it at all, it makes perfect sense to replace the bushes, and indeed the company are happy to do the work if i want them too, and no doubt in time i will get it done, but wanted to understand the specifics of why people have done it.
Rob
I have been round this fairly extensively now!! Have talked to several different engine builders and it seems that ANY PLAY AT ALL in the speed six throttle bodies will cause you an issue of some kind, whether this be going out of tune, hesitation at light throttle or proper misfire at the top end of the revs. Typically they are worn at 25-30k miles. My throttle spindles have about 0.0065" or about 0.17mm of play at worst - it seems it doesn't take much at all to cause an issue! They have done 32k miles.
With regards going out of tune - well, this is the easiest to diagnose i guess, small movements in idle position can have a big proportionate affect on airflow, and the throttle pot internals can also start to wear with vibration which affects their accuracy.
With regards to hesitation at very light throttles, butterfly valves still fairly horizontal in the body will vibrate up and down due to airflow 'pulsing' i.e. no real vacuum. This vibration has a double whammy effect, it will change the airflow to a small degree, but overriding this it will rapidly change back and forth the apparent position in the throttle pot, causing fuelling to change and a rich / lean mixture in a very mixed up way!
With regards to the misfire at high revs, this is again due to vibration. at around 6k the airflow is extremely high and causes high frequency vibration (there must be a harmonic around this combination of airflow and engine speed i guess) on the now vertical throttle butterfly, which in turn vibrates the hell out of the throttle pot and causes the misfire, in some bad cases it can momentarily stall the ignition system due to an overload of data from the throttle pots.
The absolute engineering solution seems to have been undertaken by Dreadnought TVR, I had a good chat with them and their understanding of this problem is extremely good. Roller bearing fixes are done by Str8 Six and Racing Green, but talking to Dreadnought a roller bearing fix isn't ideal either due to issues around low stiction with bearings and a further vibration caused by airflow, but, i guess these must work adequately or people would not have bought them and been happy. Im not advocating one or the other but simply to say that the bearing fix is cheaper than a special, bespoke bush arrangement that Dreadnought use. I havent been able to find an engineering company that will do it any cheaper that the guys that currently do it and are practiced hands.
Im going to go with a roller bearing fix simply because i don't have the funds for the Dreadnought solution at around £900. It will solve my going out of tune issue and high end misfire if nothing else.
Rob
With regards going out of tune - well, this is the easiest to diagnose i guess, small movements in idle position can have a big proportionate affect on airflow, and the throttle pot internals can also start to wear with vibration which affects their accuracy.
With regards to hesitation at very light throttles, butterfly valves still fairly horizontal in the body will vibrate up and down due to airflow 'pulsing' i.e. no real vacuum. This vibration has a double whammy effect, it will change the airflow to a small degree, but overriding this it will rapidly change back and forth the apparent position in the throttle pot, causing fuelling to change and a rich / lean mixture in a very mixed up way!
With regards to the misfire at high revs, this is again due to vibration. at around 6k the airflow is extremely high and causes high frequency vibration (there must be a harmonic around this combination of airflow and engine speed i guess) on the now vertical throttle butterfly, which in turn vibrates the hell out of the throttle pot and causes the misfire, in some bad cases it can momentarily stall the ignition system due to an overload of data from the throttle pots.
The absolute engineering solution seems to have been undertaken by Dreadnought TVR, I had a good chat with them and their understanding of this problem is extremely good. Roller bearing fixes are done by Str8 Six and Racing Green, but talking to Dreadnought a roller bearing fix isn't ideal either due to issues around low stiction with bearings and a further vibration caused by airflow, but, i guess these must work adequately or people would not have bought them and been happy. Im not advocating one or the other but simply to say that the bearing fix is cheaper than a special, bespoke bush arrangement that Dreadnought use. I havent been able to find an engineering company that will do it any cheaper that the guys that currently do it and are practiced hands.
Im going to go with a roller bearing fix simply because i don't have the funds for the Dreadnought solution at around £900. It will solve my going out of tune issue and high end misfire if nothing else.
Rob
Daston said:
Is this a case of some will do it and others wont?
Mine is an early one too (2000 reg) but it does hold its tune for most of the year, it slowly starts getting worse within 6 weeks of a service.
Can you add bushes to the early ones to make it any better without going the whole hog of upgrading to bearings?
Personally, if your going to do the work to put bushes in, do that little bit extra and put bearings in. If the small amount of play i had was cuasing a problem, bushes may fix the problem in the short term, but it will return as bushes wear - and it wouldnt take long to get a similar amount of wear with bushes. Mine is an early one too (2000 reg) but it does hold its tune for most of the year, it slowly starts getting worse within 6 weeks of a service.
Can you add bushes to the early ones to make it any better without going the whole hog of upgrading to bearings?
Edited by Robertjp on Thursday 14th January 09:09
so called said:
I had my Mk1 Tuscan done by Jason @ Str8Six.
Made a big difference.
Mine was a 2000 and had a LOT of play. almost impossible to tune and felt like it hadnt been done a week later.
It quietend the mechanical noise down considerably and from my point of view was the best 600 quid I spent..........apart from the rebuild and the new shocks and springs and the SP12's and.............
And as I've mentioned a thousand times now I then wrote her off. Life can be a real b
h some times.
My Mk2 Convertible seems fine at the moment with 33k on the clock.
As far as the best way to fix the problem, I have heard arguments for and against roller bearings.
I heard that TVR considered bearings and then dropped them as the wrong solution but then Jason was a TVR engine man and was fully aware of the various issues and corrective action that TVR identified and which ones were identified as affordable corrections or just left unmodified. Some decisions were not based on best but most cost effective.
I think that high quality bushes or roller bearings will both provide a good solution and the effect will obviously depend on how old / worn your S6 throttle bodies are.
In my case it was dramatic. You should have seen the smile on my face when I drove from Henley back up to Cheshire. Great.
Its a real shame you couldnt rescue the engine - or even just pinch the throttle bodies!!! Made a big difference.
Mine was a 2000 and had a LOT of play. almost impossible to tune and felt like it hadnt been done a week later.
It quietend the mechanical noise down considerably and from my point of view was the best 600 quid I spent..........apart from the rebuild and the new shocks and springs and the SP12's and.............
And as I've mentioned a thousand times now I then wrote her off. Life can be a real b
h some times.My Mk2 Convertible seems fine at the moment with 33k on the clock.
As far as the best way to fix the problem, I have heard arguments for and against roller bearings.
I heard that TVR considered bearings and then dropped them as the wrong solution but then Jason was a TVR engine man and was fully aware of the various issues and corrective action that TVR identified and which ones were identified as affordable corrections or just left unmodified. Some decisions were not based on best but most cost effective.
I think that high quality bushes or roller bearings will both provide a good solution and the effect will obviously depend on how old / worn your S6 throttle bodies are.
In my case it was dramatic. You should have seen the smile on my face when I drove from Henley back up to Cheshire. Great.
Edited by so called on Wednesday 13th January 22:24
TUS 2 CON said:
This is really interesting.
My car (2005 'vert) suffers from hestitation at around 2250 to 2750 revs and I kangaroo down the road like a learner. This is particularly irritating because (a) like a good Speed Six owner, I drive at low revs until the engine is warmed up, and (b) living in Central London, I don't often get a chance to go further up the rev range!
How many miles have you done? Rumour has it the bushes were introduced for 2005 cars. Its not hard to check, get your airbox off and check for play in the spindles on the throttle bodies. If you're not sure go over to Jason at Str8 six and get him to check...he isnt too far from London in Lewknor nr Oxford. My car (2005 'vert) suffers from hestitation at around 2250 to 2750 revs and I kangaroo down the road like a learner. This is particularly irritating because (a) like a good Speed Six owner, I drive at low revs until the engine is warmed up, and (b) living in Central London, I don't often get a chance to go further up the rev range!
Edited by TUS 2 CON on Wednesday 13th January 00:28
Have received my new modded TB's from RG now, and the machining of them for the throttle bodies is good.
BUT, im not impressed with the state of the rest of the TB's, my old ones were in better condition
.
In general, its cosmetic, burrs here and there, like for instance the fuel hose faces have been used for holding for machining and they are all burred. The butterfly mechanical arms still have witness marks and indentations from where the small grub screw has dug in and scored the face of the arm. The engine clamping faces arent completely smooth either, slight burrs etc.
So, it means a day of cleaning up with the dremel, grinding stones and some scotchbrite! All can be corrected and there is no play where there shouldn't be, but just be aware your not getting new TB's from RG...and when they say 'reconditioned' that doesnt necessarily refer to the whole thing!!!
BUT, im not impressed with the state of the rest of the TB's, my old ones were in better condition
. In general, its cosmetic, burrs here and there, like for instance the fuel hose faces have been used for holding for machining and they are all burred. The butterfly mechanical arms still have witness marks and indentations from where the small grub screw has dug in and scored the face of the arm. The engine clamping faces arent completely smooth either, slight burrs etc.
So, it means a day of cleaning up with the dremel, grinding stones and some scotchbrite! All can be corrected and there is no play where there shouldn't be, but just be aware your not getting new TB's from RG...and when they say 'reconditioned' that doesnt necessarily refer to the whole thing!!!
Edited by Robertjp on Tuesday 19th January 09:16
Edited by Robertjp on Tuesday 19th January 09:17
Im fitting them next week...have a few days off.
I am replacing the throttle pots too, but even if i wasnt, when taking them off the old set and putting them back on the new set you should then reset the throttle pot positions before doing the throttle balancing and idle reset. This needs the laptop and a synchrometer.
If you can wait a week or 2 i will let you know if it has solved my problem!
....oh and im glad my name isnt Tony. Having said that, im still not taking any chances!!
I am replacing the throttle pots too, but even if i wasnt, when taking them off the old set and putting them back on the new set you should then reset the throttle pot positions before doing the throttle balancing and idle reset. This needs the laptop and a synchrometer.
If you can wait a week or 2 i will let you know if it has solved my problem!
....oh and im glad my name isnt Tony. Having said that, im still not taking any chances!!
RM75 said:
Thanks Rob. Apologies if this is a stupid question, but when STR8-SIX changed a throttle pot on my car a couple of months ago, they just let it idle afterwards, and after about 30 seconds the 2 sides of the car equalised by themselves (or so it seemed).
If I'm reusing my throttle pots will it not just sort itself out again?
Edited to add:- the main reason I ask this is that I have the diagnostic software, but don't have a lead or laptop to run it on. And I don't know what the hell I'm doing either! :-)
Not sure i know either, but i am learning as i go along!! I set the cerby up myself and watched the professionals do it, the speed 6 isnt all that different - still has two separate banks to balance. If I'm reusing my throttle pots will it not just sort itself out again?
Edited to add:- the main reason I ask this is that I have the diagnostic software, but don't have a lead or laptop to run it on. And I don't know what the hell I'm doing either! :-)
Edited by RM75 on Monday 25th January 18:19
Im not sure on the answer to your question to be honest - i would be very surprised if a throttle pot could be replaced without 'zero' positioning...the software has no way of knowing where it is. I will stand corrected, but cant see it myself. Give Jason a call and ask i guess? If anyone knows he will!
shep1001 said:
Just got mine back from Str8six. Significantly different, drives smoother, more responsive to light inputs to the throttle, better tick over when warm. Has been too wet yesterday & its icy today 
to give it beans and see if it makes a difference when going for it. Don't want to end up posting like the poor chaps on the last page!!
Shep
What were your symptoms shep? out of tune quickly? hesitant at light throttle? to give it beans and see if it makes a difference when going for it. Don't want to end up posting like the poor chaps on the last page!!Shep
Good to hear it feels nice. Jason seems to have lead the way with this mod...Hopefully fitting mine Tuesday...
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