CR throttle body balancing

[88V8]

No it doesn't. Surely it isn't meant to have either? It has just one 99 and then the three sets of butterflies are set up against each other with the adjustment screws which are mounted onto the spindless. I don't believe I am missing any parts. Put another way, the throttle rod (99) is connected to the linkage between the front and middle throttle bodies. The adjustment screw sets the balance between them. Meanwhile there is an adjustment screw between the middle and rear bodies as well which means that the rear set respond to the movement in the middle set - which is responding to the main throttle link rod (99). As I understood it, this is why they are so s..t.

 

Oh dear. The original linkage on my CR had three rods, but someone did say it might not have been original. Was knackered and went in the bin all the same.

I sit corrected.

 

I imagine your setup would have worked OK when new, but I can see that with one set levering off another, any wear would accumulate and make things pretty tricky.

 

Well, start with it all under tension from the throttle cable so the slack is gone, and work from there.

 

May be worth putting a Wanted in the Trade section in case someone has a decent linkage going spare.

 

Ivor

[Peter Cobbold]

Quentin

Yours is definitely a CR series linkage - same as my '74CR was. I remember seeing the front butterflies opening before the other two pairs -just as you decribe. I do remember - going back 20 years this! - closing up the 20-30 thou clearance with the nylon roller. And maybe I replaced the the roller- it was IIRC grooved badly. The top location of the adjustment rod was also dodgy allowing it to rock. As you can see the unsynchronised movement of the butterflies its very much a question of looking for the lost motion and eliminating it. And you're going to have to find it even with an air meter!

Peter

[Quentin]

Rob, I thought would check the alignment of my throttle bodies and sure enough they are all over the place. The rear one is on quite a signficant angle. I would never have thought to look. Thanks. I'll put that right at the first opportunity! Not sure where the TD head dowell pin is though.

Q

[Rob Salisbury]

Rob, I thought would check the alignment of my throttle bodies and sure enough they are all over the place. The rear one is on quite a signficant angle. I would never have thought to look. Thanks. I'll put that right at the first opportunity! Not sure where the TD head dowell pin is though.

 

 

Hi Quintin, not TD!,...TB... Throttle Body.... each TB has a center dowel pin that locates it on the head, it is then clamped to the head by the manifold studs and little bridging pieces, I found it easier to get all three TBs level if the center TB did not have the dowel pin and was just located by the manifold studs.

Cheers Rob

[Quentin]

Well so far my findings are typical of the PO. I only have the top nuts securing the TBs. The studs are not there either I bet the dowels aren't either! Having said that when I loosed the nut on the rear TB it wouldn't budge. This suggests to me he has used some kind of sealant to affix it tight in the absence of the bottom studs and nuts. So, I have now resigned myself to completely removing The TBs and exhaust manifold because I expect the gasket will get damaged .

 

As a point of note, the front TB is fitted noticeably higher than the middle one. This may well cause unexpected influence on the middle TB spindle, possibly leading to less direct linkage and hence my problem. Oh well. Down to Moss tomorrow for gaskets, studs and dowels just in case.

 

Thanks Rob for the tip about levelling the TBs. I wouldnt have looked but now its bleeding obvious! Here's hoping it's the main cause!

 

Talking of sealant, if I do have to change the gasket, should I use any? and if so, both sides of the gasket and what sealant.

Cheers

Edited June 8, 2011 by Quentin

[Peter Cobbold]

Well so far my findings are typical of the PO. I only have the top nuts securing the TBs. The studs are not there either I bet the dowels aren't either! Having said that when I loosed the nut on the rear TB it wouldn't budge. This suggests to me he has used some kind of sealant to affix it tight in the absence of the bottom studs and nuts. So, I have now resigned myself to completely removing The TBs and exhaust manifold because I expect the gasket will get damaged .

 

As a point of note, the front TB is fitted noticeably higher than the middle one. This may well cause unexpected influence on the middle TB spindle, possibly leading to less direct linkage and hence my problem. Oh well. Down to Moss tomorrow for gaskets, studs and dowels just in case.

 

Thanks Rob for the tip about levelling the TBs. I wouldnt have looked but now its bleeding obvious! Here's hoping it's the main cause!

 

Talking of sealant, if I do have to change the gasket, should I use any? and if so, both sides of the gasket and what sealant.

Cheers

 

 

Quentin,

No wonder it ran rough!!

The gasket also serves as the exhaust gasket - its one piece. No sealant on the exhaust area, maybe not on inlet either if mating surfces of inlet manifolds are flat.

The inlet manifolds dont have dedicated bottom studs - studa are shared with exhaust using bridge pieces.

The lugs on the underside of the ali manifolds where the bridge-piece locates may be dog-eared and you might need to build them upwith Technoweld to get a solidly clamaped manifold.

You can almost certainly just tug the exhaust manifold outwards without disturbing connection with pipes.

Peter

[JohnTB]

Check your servo non return valve. I suffered from a similar experience some months ago after fitting a new servo. The effect is the hesitancy on pick up you describe due to (in my case) the servo stealing all the vacuum from the MU. My non return just didn't exist and after fitting a new one, all was just fine. Long shot I know, but worth a try.

[Quentin]

Right, so I removed all the throttle bodies, fitted a new gasket and reinstalled. They are now all perfectly lined up. End result is comprehensively worse than before Blimey! However, it is apparent that the spindle on the front TB has play in it, I can make it move up and down. I expect this is the key culprit. As it happens I have a spare front TB but the butterflies are a bit gappy. So this evening I put the butterflies from the current TB into the spare and interestingly they fit better. I still have a little play but much less. Actually i measured the diameter of the spindle and you won't be surprised to know that it is not round! I have up to 0.12mm difference (worst at the lever end). Seems like a lot but as I said it doesn't feel like much play when fitted.

 

Anyway I'm on a no lose path at the moment. I thought i would swap the air bleed valve from the rear balance pipes to the front and plug the back one as Roger Williams for a better AFR. That will be interesting.

 

Meantime, I have posted a wanted ad for some new CP TBs Btw, nrv on servo is good so probably not responsible for the hesitation.

Edited June 13, 2011 by Quentin

[Davidw]

I hope this isn't too late but, Quentin, whatever you do, DON'T clean the insides of the TBs. The carbon build uop in there helps the seal to the discs. I cleaned mine up a year ago and they're still not quite right some 3000 miles later.

[Quentin]

Thanks for that advice. I had read that elsewhere so I can confirm they went back in just as coked up as they came out. Didn't feel right doing that though!

 

Anyway BINGO! My newly fettled spare throttle body went on the car yesterday afternoon and immediately it was obvious that there was no visible play. Better still all three TBs now move together I balanced as best I could without a synchro meter and it is now really pretty good. Not perfect and I am still getting a little hesitation when accelerating from idle.

 

Moving the idle screw to the front balance pipe has also made a noticeable (though not dramatic) improvement in idle smoothness. This should get better of course when (or more likely if) all three TBs are perfectly synced.

 

In summary therefore, I reckon I am nearly there with my new MU, new Injectors and newly fettled TBs. I am not sure though that the small hesitation will be fixed even with perfectly synced TBs. Some other cause perhaps? I checked the NRV on the servo and that's fine. I am a bit confused about the adaptor for the servo vacuum tube on the air manifold. In the Moss and Rimmer catalogues (CR inlet manifold pages) this looks like a simple adaptor (21K8342) and mine is just that. However, when you look at both Moss and Rimmer catalogues for the Servo, they both show the same device again - but as an NRV - Part no. ADU1402. I would welcome some input on this. Actually I may post a separate question about this later just in case I've bored everyone to death with this thread and I don't get an answer

[88V8]

I balanced as best I could without a synchro meter and it is now really pretty good. .

I am a bit confused about the adaptor for the servo vacuum tube on the air manifold. In the Moss and Rimmer catalogues (CR inlet manifold pages) this looks like a simple adaptor (21K8342) and mine is just that. However, when you look at both Moss and Rimmer catalogues for the Servo, they both show the same device again - but as an NRV - Part no. ADU1402.

Well persisted with the balancing.

 

My servo takeoff is, as you say, just a connector on the middle tb. The NRV is on the servo, the black push-in thing.

An additional NRV would do no harm I suppose, but I see the Moss list gives model years 62-67 for ADU 1402. Perhaps at that time the servo lacked its own NRV.

 

Ivor

[Peter Cobbold]

Hesitation when accelerating from idle might be due to lack of transient enrichment inherent in the PI design. As you open the butterflies the mixture should be enriched (as it is in most carbs) but it will go weaker because the air flow increases instantly yet the fuel injection has to catch up. So ensure the MU diaphragm and cam follower moves as fast as possible - as its new, all I can suggest is a little lubricant sprayed inside that plastic cover on the 'castle'.

 

The transiently lean mixture upon opening the throttle from idle will burn slower so the normal spark timimg will be a bit retarded for it (hence the hesitation). I would be inclined to connect the vac advance capsule to a throttle-edge take-off. Then as you open the throttle the fast air flow around the top of the part-open butterfly creates some 'vacuum' that will advance the timing via the capsule. As the throttle opens more that vacuum will cease and timing returns to normal. (At idle the throttle edge take-off is on the plenum side of the butterfly so no vacuum or advance.)

[Quentin]

Thanks Ivor I missed that. That explains it.

 

Peter, I have been thinking of doing exactly that. Not least because my engine is a Mark II PI saloon engine (125BHP - basically the CR) and as I understand it the Saloon used the vacuum advance. For £2 for a vac. advance pipe from Chris Witor I figure it is a worthwhile cheap thing to try. Maybe I'll get better efficiency to boot. I read a recent post about this in which you contributed. It had a spark advance table someone (Nick?) posted. Looks very interesting. I don't really understand why with the same engine (and pretty much setup) the saloon used vac. advance and the TR not. Also, I note that whereas everyone wants me to set my timing to circa 13deg BTDC, it's much happier (and stronger) at circa 8 deg BTDC which as it happens is exactly where the saloon book says it should be. Except they have the same CAM as well so why would it be different? Could this be the disy set up?

[Peter Cobbold]

Thanks Ivor I missed that. That explains it.

 

Peter, I have been thinking of doing exactly that. Not least because my engine is a Mark II PI saloon engine (125BHP - basically the CR) and as I understand it the Saloon used the vacuum advance. For £2 for a vac. advance pipe from Chris Witor I figure it is a worthwhile cheap thing to try. Maybe I'll get better efficiency to boot. I read a recent post about this in which you contributed. It had a spark advance table someone (Nick?) posted. Looks very interesting. I don't really understand why with the same engine (and pretty much setup) the saloon used vac. advance and the TR not. Also, I note that whereas everyone wants me to set my timing to circa 13deg BTDC, it's much happier (and stronger) at circa 8 deg BTDC which as it happens is exactly where the saloon book says it should be. Except they have the same CAM as well so why would it be different? Could this be the disy set up?

 

 

Quentin,

See recent posts by Dave Dawson who did just that - he also has ex-saloon manifold- and gets 4-5mpg better. Re 13 vs 8 BTDC: best way to set up 'static' timing is to slowly rotate disy until you have max rpm , but ensure you keep rpm below the start of centrifugal advance. Optimum timing depends on CR, mixture cam etc. You then just have to hope the standard c/f adv curve is about right for your engine - it wont be far off. Sounds like you have found the best static advance yourself - but does that 8 deg setting give the stumbling pickup? Try different static timings to see where the pickup stumble is least.

I dont know why the saloon and TR6 were different - cheap enough to connect up the adv capsule! The saloon will be heavier so perhaps needed vac advance to help the longer time spent during pick-up from low speed?? Or maybe thye thought TR drivers dont care about fuel consumption and saloon drivers do... Puzzling.

Peter

Edited June 15, 2011 by Peter Cobbold

[Andy Moltu]

all I can suggest is a little lubricant sprayed inside that plastic cover on the 'castle'.

 

 

 

 

All you have under the plastic cover of the castle are the mixture adjustment rings which don't move (unless the locking rings have come loose) so lubricating them won't have any effect on performance. The accessible moving parts are beneath the rectangular plastic cover - in theory you could spray lubricant here but in doing so you'd have to unscrew it and in the process disturbing the security seal on the screws and invalidating your warrant on the metering unit (assuming it's under warranty).

 

99 time out of a hundred rough low speed running and hesitancy at light throttle is down to throttle imbalance- the CR throttle system is a pig to adjust well when in A1 condition and virtually impossible when worn - one throttle acts on the next which acts on the next.

If it's worn bin it & get a Revington one or a Reg Bowler one. My experience with the other supplier is that they use (or certainly used to)metal bushes which can go very tight if the manifolds are minimally out of alignment. (Revington & Reg use nylon or PTFE bushes which are less prone to getting tight when hot)

Edited June 16, 2011 by andymoltu

[Quentin]

Thank you both. Last night was the Brunel Group and Happily Badshead has a synchro meter I can borrow. So, we'll see if I can truly balance them

[Davidw]

Please forgive for hijacking this thread, but where can I obtain this vacuum advance (for a CP car) and to what do I connect it? I assume that one end goes to the Dizzy diaphragm thingy but what about the other? Can I just add a junction to one of the pipes from the inlet manifold (& if so which one?) or am I going to have to bore holes in something and if so what and what size and what do I tap into it?

 

I ask because this seems from what you are all saying to be a cheap way of saving a lot of petrol for no fall off in performance.

[Quentin]

Umm, well I am assuming I can connect it to the front throttle body which is currently plugged off. Unscrew the plug and fit another adaptor. My spare front throttle body (which was from a saloon) already has that adaptor in place though I don't know if it is supposed to be there. Peter? - you mentioned teeing off from the servo tube.

 

Look up Chris Witor web site, he sells the tube for £2.00!

Q

[Quentin]

Hmm just looked at some saloon engine pics on google and apparently that's not it. Not sure

[Peter Cobbold]

Umm, well I am assuming I can connect it to the front throttle body which is currently plugged off. Unscrew the plug and fit another adaptor. My spare front throttle body (which was from a saloon) already has that adaptor in place though I don't know if it is supposed to be there. Peter? - you mentioned teeing off from the servo tube.

 

Look up Chris Witor web site, he sells the tube for £2.00!

Q

 

 

Quentin,

To tee into either the servo hose or the hose to MU you'd need a reducing tee connector, something like these:

http://www.advancedfluidsolutions.co.uk/barbed-reducing-hose-t-piece-connectors-59-c.asp

But if your ex-saloon front throttle body has the take-off built-in you wont need it.

Peter

[Peter Cobbold]

Please forgive for hijacking this thread, but where can I obtain this vacuum advance (for a CP car) and to what do I connect it? I assume that one end goes to the Dizzy diaphragm thingy but what about the other? Can I just add a junction to one of the pipes from the inlet manifold (& if so which one?) or am I going to have to bore holes in something and if so what and what size and what do I tap into it?

 

I ask because this seems from what you are all saying to be a cheap way of saving a lot of petrol for no fall off in performance.

 

 

David,

See my reply to Quentin above, no drilling.

Yes it should advance the timing at cruise without upsetting performance. There is a possibility that there might be (more?) tendency to pink on opening the throttle from cruise to full load, depends on engine and MU etc. But I agree for very little cash and little effort its worth trying. Let us know how it goes.

Peter

[smizgals]

Please forgive for hijacking this thread, but where can I obtain this vacuum advance (for a CP car) and to what do I connect it? I assume that one end goes to the Dizzy diaphragm thingy but what about the other? Can I just add a junction to one of the pipes from the inlet manifold (& if so which one?) or am I going to have to bore holes in something and if so what and what size and what do I tap into it?

 

I ask because this seems from what you are all saying to be a cheap way of saving a lot of petrol for no fall off in performance.

 

 

A Fuel Trap, as in http://www.revingtontr.com/shop/catalogue_page.asp?mscssid=2bw1a07aprws8hvwdjrsu3hx3tdn2ha0&PlateID=430&PlateTitle=Catalogue+Page+TR6CRCF+%2D+20%2D29+%28ENGINE+%28CARBURETTOR+MODELS%29%29&PlateImage=20%2D29%2Ejpg&CarType=TR6CRCF

 

is also recommended.

 

Stan

[Peter Cobbold]

A Fuel Trap, as in http://www.revingtontr.com/shop/catalogue_page.asp?mscssid=2bw1a07aprws8hvwdjrsu3hx3tdn2ha0&PlateID=430&PlateTitle=Catalogue+Page+TR6CRCF+%2D+20%2D29+%28ENGINE+%28CARBURETTOR+MODELS%29%29&PlateImage=20%2D29%2Ejpg&CarType=TR6CRCF

 

is also recommended.

 

Stan

 

Yes on a carb engine, but I would think not for PI as injectors are down wind of the va take-off.

Diaphragm could be suspect on old disys, possibly never part of recon procedures?

[smizgals]

Yes on a carb engine, but I would think not for PI as injectors are down wind of the va take-off.

Diaphragm could be suspect on old disys, possibly never part of recon procedures?

 

 

What about blowback? Not a huge expense for peace of mind.

[88V8]

Before I started fitting a vac advance, I'd want to know why the factory omitted it. Can't believe it was cost, after all the dizzy already has the capsule.

 

Ivor