john.r.davies Posted March 26, 2018 Report Share Posted March 26, 2018 Inspired by a thread on the TR4 Forum http://www.tr-register.co.uk/forums/index.php?/topic/65490-rebuilt-engine-overheating/&do=findComment&comment=575458but not wishing to hijack that, may I ask a similar Q? I rebuilt a 2L engine for my Vitesse, Tr6 cam shaft, Lucas Pi fuelling. It has a raised CR, 10.5:1, flowed head, roller rockers, 6-3-1 manifold. I dismantled and rebuilt the throttle bodies, because one had been sticking, wide open! The engine now has 2K miles on it, so 'run in' . It idles fast from cold, 1.5-2K even with the idle control as closed as possible, and as it warms up, idles faster and faster, until it's idling at 3K! It doesn't overheat as such but tends towards the top of the heat range (Electric fan) and if turned off from this situation is very difficult to restart. I've checked and reset the butterflies, to grip all-round a feeler gauge of 1.5thou, and tested the running engine with brake cleaner spray, including the ends of the throttle spindles, to find no evidence of a leak. I'll be grateful for ideas about why this fast idle! John Quote Link to post Share on other sites
barkerwilliams Posted March 26, 2018 Report Share Posted March 26, 2018 John, You seem to have eliminated the fast idle being caused by all cylinders having too much air therefore it must be a rogue one or two cylinders. Why not remove a single plug lead in turn and note the effect on the idle revs. They should all have a similar effect but if one or two have a major effect that is a pointer at the cylinder(s) with a problem. Alan Quote Link to post Share on other sites
RogerH Posted March 26, 2018 Report Share Posted March 26, 2018 Hi John, how is the ignition timing. If too advanced it raises the revs.. Roger Quote Link to post Share on other sites
Mike C Posted March 26, 2018 Report Share Posted March 26, 2018 I'd check the manifold vacuum at idling. Mine is about 10 inches of mercury at 800-900 rpm. Too low a vacuum and you have an air leak somewhere. Note an easy connection point for a vacuum gauge is the brake booster manifold hose. Quote Link to post Share on other sites
John L Posted March 26, 2018 Report Share Posted March 26, 2018 Could also be a loose or not tight fitting o ring on the injector block, allowing in some air. John Quote Link to post Share on other sites
john.r.davies Posted March 26, 2018 Author Report Share Posted March 26, 2018 All wise words, which I shall implement - but not for a few days. I have assignments to write! Thnank you all, and if any other gurus have further ideas - they shall be used! John Quote Link to post Share on other sites
jerrytr5 Posted March 26, 2018 Report Share Posted March 26, 2018 Have you put a synchrometer on the inlets? Very difficult to set the idle without one in my experience. Jerry Quote Link to post Share on other sites
DaveN Posted March 27, 2018 Report Share Posted March 27, 2018 Blank off the vacuum hose to the brake servo! Dave Quote Link to post Share on other sites
astontr6 Posted March 27, 2018 Report Share Posted March 27, 2018 Inspired by a thread on the TR4 Forum http://www.tr-register.co.uk/forums/index.php?/topic/65490-rebuilt-engine-overheating/&do=findComment&comment=575458but not wishing to hijack that, may I ask a similar Q? I rebuilt a 2L engine for my Vitesse, Tr6 cam shaft, Lucas Pi fuelling. It has a raised CR, 10.5:1, flowed head, roller rockers, 6-3-1 manifold. I dismantled and rebuilt the throttle bodies, because one had been sticking, wide open! The engine now has 2K miles on it, so 'run in' . It idles fast from cold, 1.5-2K even with the idle control as closed as possible, and as it warms up, idles faster and faster, until it's idling at 3K! It doesn't overheat as such but tends towards the top of the heat range (Electric fan) and if turned off from this situation is very difficult to restart. I've checked and reset the butterflies, to grip all-round a feeler gauge of 1.5thou, and tested the running engine with brake cleaner spray, including the ends of the throttle spindles, to find no evidence of a leak. I'll be grateful for ideas about why this fast idle! John Hi John! Are you certain that there is no air leak between one of the manifolds and manifold gasket. i.e. one of the clamps loose or missing or not properly positioned. I lost the complete assembly! stud and all. It gave me this problem! Bruce. Quote Link to post Share on other sites
john.r.davies Posted March 30, 2018 Author Report Share Posted March 30, 2018 Thanks to all! barkerwilliams - only slight, and equal change on disconnecting a spark plug. Roger - timing not as far advanced as I'd like, and v.modest - that's the one way to controll the idle speed that I can find. Mike C, and Dave N, brake booster? What brake booster? I'm sure I have a vacuum gauge somewhere, if only I can find it. John L, O-rings on the injector?!! Now there's a thought. They are all tight in the throttle bodies, and a spray of brake cleaner on them does nothing, but new O-rings! jerry, I have synchrometered them, I'll do it again. Bruce, I'm beginning to think there must be a leak somewhere, and at the gasket is most likely. Thanks to all! As Bruce says, the most likely is an air leak. I wondered (hoped) someone could think of something else. All I need is time! John Quote Link to post Share on other sites
Mike C Posted March 30, 2018 Report Share Posted March 30, 2018 "f turned off from this situation is very difficult to restart"- indicates an air leak that gets worse as the engine heats up. Quote Link to post Share on other sites
DaveN Posted March 31, 2018 Report Share Posted March 31, 2018 Ah of course no brake servo on the Vitesse! Quote Link to post Share on other sites
TriumphV8 Posted March 31, 2018 Report Share Posted March 31, 2018 Thanks to all! As Bruce says, the most likely is an air leak. I wondered (hoped) someone could think of something else. All I need is time! I think you already know its an air leak. The only comfortable check I would offer from the note of the difficult restart is that you can let the engine idle some time and check the spark pugs. If the leaking at the throttle plate becomes quite big the compensation between the six lines might suffer and some go lean and some rich what might have an influence on the starting. That should be found on the plug colour. Quote Link to post Share on other sites
John L Posted March 31, 2018 Report Share Posted March 31, 2018 Have you done a tongue test on the MU itself? Quote Link to post Share on other sites
barkerwilliams Posted March 31, 2018 Report Share Posted March 31, 2018 John, My experience of the PI is that if the metering unit was delivering too much fuel there would be a small rise in revs and then the mixture would get very, very rich and the engine would stutter and the revs could not rise to the 3k you reported. Air is needed to burn the enrichened mixture and without a good supply the revs cannot rise. If one of the throttle bodies gaskets is leaking there would be an uneven amount of power /revs been driven by one or two cylinders hence my question regarding pulling plug leads and you report the idle is been maintained by all cylinders. My TR6 originally idled on two cylinders, the other four just running too rich and effectively not contributing. Air must be getting in somewhere and then been distributed to all cylinders. Do you have the 125 throttle bodies with the two balancing tubes, or the 150 with a single balance tube between the throttle bodies? Alan Quote Link to post Share on other sites
Waldi Posted March 31, 2018 Report Share Posted March 31, 2018 Quote: I've checked and reset the butterflies, to grip all-round a feeler gauge of 1.5thou, and tested the running engine with brake cleaner spray, including the ends of the throttle spindles, to find no evidence of a leak Unquote Hi John, In your first post you indicate you have set the butterflies at 1.5thou. Can you (ir did you) close all 3 TBs just a bit (not fully closed, just a bit) and see if this makes a difference? Good luck, you will get there. Waldi Quote Link to post Share on other sites
Colin White Posted March 31, 2018 Report Share Posted March 31, 2018 In my experience the butterflies need to be compltely closed so the air flow is controlled by the needle valve. When setting mine I found that if you can see light with the butterflies closed when looking through the throttle bodies (off the car) the idle speed is too high even with the needle valve closed. Quote Link to post Share on other sites
john.r.davies Posted March 31, 2018 Author Report Share Posted March 31, 2018 (edited) Checked the butterflies again. First with the Synchrometer, which found that the front TB was flowing most. Tried with the feeler, 6 & 5 gripped a 1.5 thou feeler firmly, 4 & 3 less so, and 2 & 1 only just. So, played with the setting of the overhead throttle linkage, until the others gripped the feeler. Made a slight difference, but then found that while I'd been checking below the butterfly, above them they weren't so tight. Maybe I need to reset the butterfly discs in the throats again? Get them more central. Dark now! Thanks to all, it does look as if it is this tiny leak around the butterflies. John Edited March 31, 2018 by john.r.davies Quote Link to post Share on other sites
wheeler Posted March 31, 2018 Report Share Posted March 31, 2018 HiJohn I have just had similar problem after removing the head to replace the pistons on my TR6 with CR throttle linkages, not sure what you have on the Vitesse. On start up after replacing pistons I could not get the engine to run below 1500 RPM. After much faffing about I adjusted the linkages so that the throttle butterflies were fully closed (no feeler gauge) making sure the 'choke' cam was not opening the butterflies. I then adjusted the idle revs to 850 with the air bleed valve screw but I am not sure if you have one. Have you tried adjusting the butterflies fully closed? Try it it may help. Cheers Bill Quote Link to post Share on other sites
Waldi Posted April 1, 2018 Report Share Posted April 1, 2018 John, I replaced my 3TB shafts recently becauce the shafts were a bit worn. I cleaned the bores too, there was a vast amount of cokes in some, very close to the butterfly valve seats. I felt I could not center the disks properly with these deposits in there, dispite some recommendations here to not clean them. They were clean when they left the factory. All 6 now have a very very small moon shaped gap I closed and opened the butterfly a couple of times with screws loose, TB in vertical position (off the car). One butterfly at a time. I think they should not be fully closed at idle, as this will damage the seats after sone time. Waldi Quote Link to post Share on other sites
TriumphV8 Posted April 1, 2018 Report Share Posted April 1, 2018 I think they should not be fully closed at idle, as this will damage the seats after sone time. Waldi They are fully closed, especially with a mild cam with high vaccuum. I have them rested fully with no tension on the CP linkage. Actually i have about 1 rotation open on the idle screw. Throttle plates are large, 45mm and six of them, that little slit opened on the bottom will be on the top, too and might add to a large bypass of air at the six manifolds. Quote Link to post Share on other sites
Waldi Posted April 1, 2018 Report Share Posted April 1, 2018 Hi Andreas, I think we mean the same????. The WSM says (not full procedure, refer to chaper 19.20.05 /06 for full instructions). CP: adjust TBs until a reading of 3 is achieved with the Crypton synchro on each TB. CR: the TBs should be opened no more than 0.05 mm (2 thou), and then adjusted. John, Is the gas cable free and the lver on the MU fulky home? Regards, Waldi Quote Link to post Share on other sites
john.r.davies Posted April 4, 2018 Author Report Share Posted April 4, 2018 One suggestion above (forgive me, I forget who!) was that injector block O-rings might be leaking. I don't think so, a spray of brake cleaner on them made no difference, but O-rings cheap, and a look shows some are a bit hardened, so I've bought some new ones. The WSM say only one O-ring on each, but there are two grooves. Any harm in fitting two rings? If only to be SURE they aren't leaking! Waldi, throttle cable aand linkage checked, and choke cable also - I had that as a problem when I first fitted Pi, symptoms as listed above, but took months to doscover that the choke lever was open by a fraction. It has an accessory return spring on it now! John Quote Link to post Share on other sites
Waldi Posted April 4, 2018 Report Share Posted April 4, 2018 Hi John, This is a process of eliminating possible causes:) Did you try to close the butterflies just a bit. The 1.5 thou may be just a bit too much and then the air through the 6 butterflies is much more than the air from the air valve, as per Andreas comment above. Waldi Quote Link to post Share on other sites
Mike C Posted April 4, 2018 Report Share Posted April 4, 2018 You could find out a lot of the information on flows through butterfly by pass and the idle setting screw by connecting a vacuum gauge to the manifold somehow. Check the vacuum with each set to your setting and then again with each fully closed. I know my engine needs 10" Hg to idle with my particular PI system and cam - anything less and I have to fix it. Is the old "cigarette paper" method of setting the butterflies still in use? (Maybe today's cigarette paper is of a different thickness to 1970's cigarette paper? Different times different tobacco's.) Quote Link to post Share on other sites
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