| Author | Message | ||
     Alan Scard New User Username: alanscard Post Number: 36 Registered: 07-2015 |
1972 Rolls Royce Silver Shadow SRH 13952 I have a loss of vacuum fault on ‘B’ bank and I want to check valve efficiency. Which cylinders are fed by which carburettor? | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 2128 Registered: 05-2012 |
Each carb feeds the outer cylinders on its own bank, and the inner cylinders of the opposite bank. | ||
| Mike Thompson Frequent User Username: vroomrr Post Number: 764 Registered: 04-2019 |
It might help if you see a picture. The holes in the manifold are separate and the right hole supplies the 4 right cylinders, and the left hole supplies the 4 left cylinders, and carbs respectively.  | ||
| Robert J. Sprauer Frequent User Username: wraithman Post Number: 473 Registered: 11-2017 |
Wrong. The intake manifold connects the right hand carb to the following cylinders - A1 B2 B3 A4 and the left hand carb is B1 A2 A3 B4. When viewed from driver's seat. | ||
| Alan Scard New User Username: alanscard Post Number: 37 Registered: 07-2015 |
Robert is correct as yesterday Mat at Introcar confirmed that the B carb is fed from A1,A4, B2 & B3 whilst A carb is fed from B1,B4,A2 & A3 cyclinder. The problem I have is the following: NO SIGNIFICANT VACUUM ON ‘B’ BANK The carburettors had been removed as a total assembly during some cosmetic activity in the engine bay. During reassembly, the Distributor Timing was checked and minor adjust made. It was considered appropriate to check the carburation - that is when the problem was found! Whilst checking: the air volume bypass screws, the jet height screws and the height of the SU pistons it became apparent that the ‘B’ Bank Carb was contributing nothing. The SU pistons were checked and found to be completely free to move. Needles and jets were correctly aligned and in good condition. The Carb to Choke trunking was removed, the weakness pipes (all pipework was sealed to arrest any air ingress) and a manometer applied to the carb throat. ‘A’ bank exhibited a healthy intake of air whereas there was a minimal volume entering ‘B’ carb. The butterfly valves are tightly secured and mechanically synchronised – they can be seen to move through the same angle when depressing the throttle. A compression test showed all cylinders were very healthy. The gasket between the carbs and the inlet manifold was replaced with a deliberate application of Hylomar Blue. No obstruction can be found in the inlet manifold. All fittings and attachments were reinstalled. The engine starts freely and runs with reasonable smoothness, there is no sensation of a misfire, however; even when hot, in neutral and the throttle depressed (to create approx. 2000 rpm,) the response is laboured and there is definitely no contribution from the ‘B’ Bank Carb – the piston rises approx. 1mm at start-up and then no more whereas the ‘A’ Bank piston rises smoothly (as both should) to approx. 15mm. PLEASE HELP. | ||
| Graham Phillips Experienced User Username: playtime Post Number: 135 Registered: 03-2019 |
G'day everyone,... Sounds like there is a leak below the carb gasket, what about the gasket between the inlet manifold and the heads? Could it be sucking air from there? I would doubt there would be any holes in the inlet manifold itself unless there is a crack in it on its underside? Just my thoughts,... Graham. | ||
| Mark Aldridge Frequent User Username: mark_aldridge Post Number: 627 Registered: 10-2008 |
If the vac leak is that significant, a length of hosepipe as a stethoscope, should detect air noise. worth a try. Even if compression test is OK, are vales sticking at running speed ? If your local garage has an old fashioned Crypton Tester, this may help Mark | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1176 Registered: 11-2015 |
Alan, Vacuum past the butterfly and a manometer at the throat are two different things. For instance a piston not moving because a vacuum passage to the top of the piston is blocked and or the gasket blocking that vacuum will cause the piston to stay low creating very low flow with a mano at the throat, but very high vacuum past the butterfly. If you piston isn't moving on that pot but 1mm, then there you go. Did anyone polish the pots when doing the cosmetics? | ||
| gordon le feuvre Frequent User Username: triumph Post Number: 308 Registered: 07-2012 |
Try swopping piston/housing side to side as matched pair. The manual is very detailed about butterfly set up/balance. Follow/read this in section "K" whilst piston/body removed from carbs As Mark says, if bad manifold gasket leak should hear. Try spraying jet brake cleaner around gasket area, does engine note change? | ||
| David Barton Yet to post message Username: daimler_darter Post Number: 1 Registered: 07-2019 |
I'm the Daimler V8 owner that has been watching with dismay the problem Alan appears to have with carburation. I'm very acquainted with SU's and that has made the problem all the more perplexing. In reply to Gordon: we have swapped the piston/housings. We have repeated the butterfly/linkage setup several times and have called on a third party to check all our techniques to ensure it conforms to the spirit of the handbook. There is no sign of a leak. Our next move is to remove the Carbs, measure vacuum at each inlet manifold inlet using an appropriate blank. If no fault found - it has to be the Carbs. There is one doubt in our minds - immediately at the rear of the Carb mount there is a square attachment held on by two screws. We know there are small ports from the choke orifice entering this device but we do not know what it does? HELP Please. | ||
| David Barton New User Username: daimler_darter Post Number: 2 Registered: 07-2019 |
Thank you Ross for your observation. One of the first thing we checked was the twin ports that feed atmosphere to the SU piston via the twin 7mm ducts in the Carb body. As for the gasket, as we tired to explain earlier, we removed the Choke ducting to fit a Gunson Manometer to the throat of the Carbs - the gasket is removed when doing that. The Carb jet-bridge/butterfly zone vacuum is fed to the SU piston via two 7mm dia holes in the base of the piston - they are definitely not blocked. This article might help: https://zparts.com/index.php/resources/su-carburetors-explained/ | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1179 Registered: 11-2015 |
David, Have you checked ignition wires at the dizzy and the timing? | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1180 Registered: 11-2015 |
David, Also, the gasket I was thinking about was the one under the casting that bolts to the intake manifold ( the one that would go on the mating surface in the photo by Mike above) | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1181 Registered: 11-2015 |
David - Alan, I didn't see, was the car running fine before the service? | ||
| Alan Scard New User Username: alanscard Post Number: 38 Registered: 07-2015 |
Hi Ross, Yes the car was running ok before. I took the car off the road to overhaul the braking system, including the 2 rams in the boot (trunk to our Americam friends). I then noticed a spot of oil on the rear drive shaft and so pulled out the complete "rear axle" and changed the drive gaitors and various oil seals plus the prop shaft universal joints. Just about to put it back on the road and the car was running ok when the rear high pressure pipe from the rear pump developed a pin hole leak. To rectify that I took off the hydraulic reservoir and various other bits to clean everything up, including the carbs as a complete unit, the distributor, coil, rocker covers as the hydraulic oil had taken the paint off. Everthing went back ok and now I have this carb problem. | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1182 Registered: 11-2015 |
Alan, Hmmmm. It would seem likely the problem lies with the ignition or the carbs. I would measure the vacuum in each bank of the manifold with the engine running. I would check that the plug wires are correct for both banks on both ends. If the carbs came off as a unit, then the gasket that goes from the carb unit to the manifold might be bad or pinched / folded whatever. Good Luck. | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1183 Registered: 11-2015 |
Alan, Did you remove the pins when fitting the gaitors or stretch it over them? | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1184 Registered: 11-2015 |
Alan - David, When checking the HT leads remember that the dizzy spins counter clockwise on that engine. When I got my car (not running) one issue was the plug leads were in the right order, just they last person to work on the car thought the dizzy spun clockwise like a chevy v8. | ||
| David Barton New User Username: daimler_darter Post Number: 3 Registered: 07-2019 |
Dear Ross, Please read our earlier posts: The engine runs quite smoothly - you can't have that situation and an ignition fault as you suggest. Be assured, we would never, ever, have confused a RR with Chevy. We explained the Carb/Manifold gasket has been replaced. We have measured the vacuum which is why we found 'B' Carb is not contributing anything. Unfortunately, your earlier thoughts on air/vacuum passages in the SU Carbs are not in accord with the http link I provided. Thanks for trying. We intend exploring this coming week - we will keep you posted. This is proving to be an interesting snag!} | ||
| Mike Thompson Frequent User Username: vroomrr Post Number: 796 Registered: 04-2019 |
David Barton, If you cannot find a solution and not a strict purist of RRs, (here comes the part many people are going to love me for ha ha) you could switch to an American carb. It is infinitely easier to deal with and will get rid of all that spider web of devices covering the whole top of the engine.  | ||
| Alan Scard New User Username: alanscard Post Number: 39 Registered: 07-2015 |
Hi Ross, I stretched the gaitors over the pins. REgards Alan | ||
| David Barton New User Username: daimler_darter Post Number: 4 Registered: 07-2019 |
Hi Mike, What a fascinating concept you suggest. Problem is: we Brits like a challenge and just because we don't fully understand a machine is why we sometimes confide in a friend. Just a small detail- the SU Carb is a very elegant solution to the 15:1 mixture task. Even an American Carb alone could not satisfy the emission legislation of 1972 which in the UK the vehicle is still required to meet - hence the pipes and gizmos. To fit such a 'thing' would probably inhibit ever revealing the engine bay to anyone ever again! Each to their own. Meanwhile: Please as asked earlier: how can we check the action of the 'weakener' device (held on with 2 screws) fitted on the underside of the Choke assembly just behind the junction of the Carbs. This device has vacuum ports in the choke and appears to provide an air bleed directly into the Choke manifold. | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1185 Registered: 11-2015 |
Alan, I put some FS ones on last year and I noticed a week ago one failed in the middle fold. I would think they would fail where you stretched them. I might go the pin route this time. | ||
| Robert J. Sprauer Frequent User Username: wraithman Post Number: 483 Registered: 11-2017 |
Much easier to press the pin out. Cut a rod or block of wood to press it back in the same distance. Always best to measure each side. I used the neck cut from a hard plastic bottle (shape like a funnel) and placed the wide end over the ball with a spray of silicone and they slid over with no effort at all. | ||
| Mike Thompson Frequent User Username: vroomrr Post Number: 800 Registered: 04-2019 |
David Barton, I have heard that even changing the hub caps (wheel covers) will cause problems for Brits. Unheard of in the USA. Possibly because your legislators have had more time to slowing turn up the heat on the frogs in order to boil them without due surprise. We in the USA are still on a simmer while the Brits are near boil. Here in Texas (where I am) they do no even open the hood (bonnet). Nor in most counties do we have emission inspections. Only centered around Dallas and Houston Texas. See: https://www.google.com/search?q=what+counties+in+texas+don%27t+have+emission+inspection But also the smog in London (was/is) is as bad or worse than in Los Angeles California. Which would be in the Brit's case having smog in Washington DC for all the legislators to put pen to paper to make laws against. | ||
| David Barton New User Username: daimler_darter Post Number: 5 Registered: 07-2019 |
Hi Mike, Our regulation is associated with Road Tax and a mandatory annual Safety Inspection (MOT). With our Classic Vehicles we are excused these, however; if we significantly change the construction or original design characteristics we lose that concession. In a few minutes we intend checking the Inlet Manifold for vacuum - will keep you posted accordingly. | ||
| gordon le feuvre Frequent User Username: triumph Post Number: 310 Registered: 07-2012 |
Alan, in theory both carbs have their butterflies set to closed as per manual and the idle stop has been just cracked to stop the butterflies hammering the inside of the carbs. If the idle stop is backed off, so that the butterflies are actually totally closed, if volume screws are the turned down totally, from there normal one and half turns out the engine should not idle at all. The point of this exercise is to confirm there is not air getting in anywhere else than through carb intakes? If this is carried out with engine running, maybe something will become apparent. Conversely if you set idle at say 800rpm, then blank intake on each carb in turn, does revs drop by similar amount? | ||
| David Barton New User Username: daimler_darter Post Number: 6 Registered: 07-2019 |
Good News: The problem is resolved. Firstly: removed the Carbs en block, measured the vacuum at the Inlet manifold - The Redex Vacuum Gauge indicated perfect balance of 11 in both ports. We turned our attention back to the Carbs. This is where we have a considerable volume of egg on our face! The 'B' Carb butterfly was no longer tightly attached to the throttle spindle. It is now apparent, the act of twitching the throttle and the high volume of air/vacuum in the Carb throat it was sufficient to make the butterfly move through approx 20 degrees independent of the spindle. Having made the clamp 'very' tight (as a Daimler person I'm not used to the need for such unrefined force) we were able to reset the linkages. The Engine now runs correctly. THANK YOU to all those who have endeavoured to help. | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1186 Registered: 11-2015 |
Alan, The last step is to drive David down to the pub for a cold one. Also, good sloothing. | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1187 Registered: 11-2015 |
Gordon, Good tip that last one about turning off the air bleed and the butterfly completely. With luck I'll never have to use it. | ||
| ross kowalski Prolific User Username: cdfpw Post Number: 1202 Registered: 11-2015 |
Robert, I ordered an axle gaiter from Flying Spares and it was not OEM rubber but a far more compliant material. I decided to just stretch it over. Put axle in vise, greased everything, pulled over in 15 seconds tops. If that is the rubber they are now made from I think the days of pressing out pins is over. The last set I ordered from FS were OEM rubber that was very stiff even when left in the sun to heat. It was a real struggle to get those ones on. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2177 Registered: 09-2004 |
For the folk who go strictly by the workshop often IMO make a dealership job justify the cost! Worth a read: http://au.rrforums.net/forum/messages/17001/29581.html?1512663326 |
