Erratic idle

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Discussion

Stunned Monkey

351 posts

208 months

Sunday 26th April 2015
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Who is Andy?

DCerebrate

Original Poster:

339 posts

109 months

Sunday 26th April 2015
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BRUTUS out for a run today, reminded of everything that is right with the Cerbera, idle problem only occurred after 20 - 30 minutes, therefore leaning towards heat-soak related air leak. Hoping to get ECU hooked up in 10 days, valves checked etc.

twinreal

300 posts

154 months

Monday 27th April 2015
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Stunned Monkey said:
Who is Andy?
http://www.pistonheads.com/gassing/profile.asp?nam...

Did my bodies, too
Very pleased with his work !

Stunned Monkey

351 posts

208 months

Tuesday 28th April 2015
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Thanks! Does he advertise anywhere what exactly he does to them?

DCerebrate

Original Poster:

339 posts

109 months

Tuesday 28th April 2015
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Hi

full advert appears on page 1, posted by crypto.
Advert mobile didn't work for me. try e-mail and Andy will send you his mobile number. andy_mr2sc (hotmail).

Andy_mr2sc

1,223 posts

175 months

Tuesday 28th April 2015
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Hi all
Very kind comments (from most anyway.)
Could I please point out the gaskets advertised on ebay on the link crypto gave are nothing to do with me but another seller by the name of pc928t.
My eBay throttle body advert can be found at:
http://m.ebay.co.uk/itm/251922807669?nav=SEARCH

as well as the Pistonheads one.

My thermo gaskets form part of the same advert. The gaskets advertised by this seller are just gasket paper.



Stunned Monkey

351 posts

208 months

Wednesday 29th April 2015
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Thanks for the info Andy, the one concern I have is with the possibility of false brinelling in the idle position. Can you use roller bearings instead? This is a job it's looking like mine'll need.

twinreal

300 posts

154 months

Thursday 30th April 2015
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Fit a new set of stiff springs and all is fine. I can't see a difference in using roller instead of ball bearings ?? The problem with the linkages is the radial movement not axial.

Stunned Monkey

351 posts

208 months

Thursday 30th April 2015
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All other things being equal, roller bearings can carry far greater loads and are therefore more robust against false brinelling.

twinreal

300 posts

154 months

Friday 1st May 2015
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Ok, but we'e talking about throttle butterflies, not i.e. half time bearing, where you have real loads.
Most important is that they are sealed against air soak.

As said, i'm very pleased with the results. I fitted new body gaskets from power (Andys will do it though) and new throttle springs and i have absolutely no shuttering or shunting. Throttle is very smooth and more direct than before.

Andy_mr2sc

1,223 posts

175 months

Friday 1st May 2015
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Apologies I've not been on here much to respond to this. I've been dragged down to the south of France by my better half for a few days. Spent yesterday around the Millau bridge. Civil engineering at its best.
Martin following your recent comments on this thread and others you made in November last year about my TB mod I will explain my actions. Yes roller bearings can take more load; they also produce more friction due to the larger surface area touching. I have tried to have the spindles moving as freely and easily as possible. You also suggested using a bushing instead of a bearing. I stayed away from this because metal rubbing metal can cause electrical interference on what is already border line circuitry. The bearings I use are more than adequate to support the loads put on the butterfly spindle. The way they are sealed and mounted means there is no chance the grease will be sucked out by the induction pressures as you suggested while air cannot be drawn through them altering the balancing.
Regarding brinneling, you sited the case where cars needed their wheel bearings replaced after a long transport on a trailer. This is a completely different situation. The cars are stationary while putting loads on the same spot on the bearings through vibration, road conditions etc. as ball bearings are moved through their travel, they naturally creep and move so when they return to idle, the balls will not always be in the same place. When the car is stationary at idle with the engine off, there will not be the same vibrations as when it is on a transporter. Maybe your car spends quite a time on the back of a transporter? How much of your cars hours of use is spent at idle with the engine running? It would take many, many hours of being in this position to start marking the bearings. As I said earlier ball bearings creep during use so the chances of the balls getting marked is minimal to nothing. IF you ever felt the bearings wear or getting notchy they can easily and cheaply be replaced with no further machining required. In fact if I was in a good mood and you sent the bodies back to me I would do this as a good will gesture.
I hope this essay clears some points up and explains the reasoning behind my methods.
Andy

m4tti

5,426 posts

154 months

Friday 1st May 2015
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The old "false brinelling" chestnut.

Andy in myth busting style how about opening one of the bearings up from your throttle bodies next winter. They've been on there for about 2 years haven't they. I'm guessing they will be "as new" inside.

Stunned Monkey

351 posts

208 months

Saturday 2nd May 2015
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Andy_mr2sc said:

Martin following your recent comments on this thread and others you made in November last year about my TB mod I will explain my actions.
I recall my previous comments were in reference to Racing Green's (then) offering of replacement with roller bearings. I also then noticed the ebay offer of ball bearings and now seek clarification of the engineering behind both.

I'm not trying to attack you or the service you offer - just to get answers in the engineering terms I too work with on a day to day basis.

As I said, I'm not convinced my TB's are healthy and at 50k miles, probably need this problem addressed, and I want to satisfy myself that the options I'm looking at are indeed the best ones.

Andy_mr2sc said:

Yes roller bearings can take more load; they also produce more friction due to the larger surface area touching.
Actually the surface area (actually a contact line, theoretically infinitely small) is more or less the same - and as a roller bearing has a constant radius, an argument could be made that a roller bearing should provide less resistance without grease.

It's the grease being forced under the rolling elements that generates the difference in rolling resistance, and will be worse on a roller. Next time I meet with our bearing people, I'll ask this question.

So... you're right, but IMO for the wrong reason - but I stand to be corrected wink

Andy_mr2sc said:

I have tried to have the spindles moving as freely and easily as possible. You also suggested using a bushing instead of a bearing. I stayed away from this because metal rubbing metal can cause electrical interference on what is already border line circuitry.
This is a new one on me - can you elaborate, are we talking static EMI? Appreciable when compared to that generated by the HT side?

I know (now) that Jenvey use PTFE-filled oilite bushes, I myself suggested something like IGUS H1 but someone else (you?) pointed out they'd tried that but had problems with sealing. I would expect a sintered phosphor-bronze bush to provide a better ground path than even a roller bearing.

...I just broke off to go check my facts on the Racing Green offering and b*gger me, they're now getting Jenvey to refurb their exchange throttle sets. This is something I had been thinking of doing, being a satisfied Jenvey customer myself.


Andy_mr2sc said:

The way they are sealed and mounted means there is no chance the grease will be sucked out by the induction pressures as you suggested while air cannot be drawn through them altering the balancing.
Is there an independent self-energising seal in-board of the bearings (eg a V-ring)? I have seen first-hand the effect on sealed bearings of vacuum much weaker than that created by an engine. Sure, it takes hundreds of hours to become apparent, which gives you 10k+ miles before any issues might appeear, but it's a predictable failure.

Andy_mr2sc said:

Regarding brinneling, you sited the case where cars needed their wheel bearings replaced after a long transport on a trailer. This is a completely different situation.
Indeed it is, but was merely cited as an example of what false-brinelling is. It's an effect which occurs when bearings are held under load in a single position and subjected to vibration. That describes idle on a throttle body pretty well IMO.

I totally agree that every movement of the throttle will redistribute the grease and hit reset on the cause, but unlike a wheel bearing of a car on a transporter, the bearings return to the exact same position every time.

Andy_mr2sc said:

How much of your cars hours of use is spent at idle with the engine running? It would take many, many hours of being in this position to start marking the bearings.
Well it depends on how often I'm stuck in traffic. Over an hour the day I bought my Cerb for example. What info do you have to back up "many hours"? Not saying you're wrong, but are we talking 5? 50? 500?

My point is that it's actually very difficult to say, and for a bearing manufacturer, very difficult to design for, other than to maximise that which gives them the best possible chance and then to test it - an approach I take every day in my job.

I've done a quick bit of googling and came across articles from NTN and NMB, both manufacturers I have worked with. I really like the look of the needle roller elements NTN feature in this article

www.ntn.co.jp/english/products/review/pdf/NTN_TR73...

In which it also states:

"Ball bearings are narrower than drawn cup bearings, but their built-in seals alone cannot completely prevent air leakage so additional seals must be incorporated"

Interestingly I cannot find any independent corroboration for my assertion about false brinelling, though one or two making reference to needle roller bearings being "resistant" in this applicaiton.

I look forward to reading your reply, and thank you for taking the time to engage, it's nice to deal with doers rather than talkers smile I'll shut up now.

Andy_mr2sc

1,223 posts

175 months

Sunday 3rd May 2015
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I must agree I cannot put a time span on the life my parts because to my knowledge none have failed yet. I think it would be fair to say they should last considerably longer than tvr's solution to drill and ream the aluminium casting!
I was considering using a secondary seal when I started looking in to this as like you say some of the other companies do but as the set up works fine without it I didn't see any point in making it more complicated and introducing another component that in time could wear or fail. The idea was to produce a simple solution that solves an on going and well publicised issue for my own personal car that I then decided to offer to fellow enthusiasts for a realistic price. I have my own cad/cam based engineering workshop so I can perform this in house. I have had repeat orders from some greatly respected Tvr specialists in the UK as well as Europe and one set has even gone to Japan. I am now working on improving other areas of tvrs, specifically the Tuscan but the RnD, cad time etc is huge.
As you obviously know from your research there are many different approaches to this problem. One of the highly respected solutions is performed by Dreadnought TVR in Scotland. They use a bronze bushing of some sort and while I don't know the exact details, the last I heard it was a £900 conversion so I would hope a lot more goes in to it than my humble approach. If you are looking for other options it could be worth talking to them or as you say, Jenvey are the top players in this field.
I am not going to continue splitting hairs so to speak about the different methods regarding bearing types, seals etc as I strongly believe that any of the offerings at all levels are a vast improvement on the standard set up. im looking forward to reading about your final decision and the results obtained.