I’ll give it a try, Pat. The tank’s now nearly full so I will try the Wynn’s Dry Fuel when it arrives and see if that works. I’ll certainly use Sta-Bil before the next winter lay-off, though.
Clive, I’ll certainly be doing that soon!
An update on the misfire problems. Firstly, the car seems to start quite readily now that the new voltage regulator is bringing the batteries up towards full charge.
Poured some Wynn’s Dry Fuel into the tank, also some Sta-bil 360 - no change to the misfire.
I performed a compression test, and it was a relief that all cylinders were more or less identical at about 165 psi, which I believe is about right for an 8:1 engine. So, no worries with sticking or burnt valves, closed-up tappets, broken rings, etc.
I pulled the plugs (brand new NGK BP5ES) to have a look. All were on the sooty side, but the 2nd from rear plug was dripping oil. I can’t say for sure that this wasn’t caused by oil having collected around the plug in the depression it sits in. Gave the plug a wash in petrol and the engine seemed to run a bit better, but still with the pesky steady-speed misfire.
Tried running the engine without the Lucas suppressor plug caps, but it made no difference.
Today, after reading an old post by Mike Balch about an XK150 with a similar problem, I reduced the points gap to .012" as recommended in the XK120 handbook. They were certainly set wider than that. I also gave them a quick file and clean. This seemed to produce a result, and there is now a marked improvement. There is still a slight misfire with the engine held at a steady speed, though.
I can’t be sure I got the points gap quite as accurate as I’d like - it’s a pig to get at in situ, as you know. I have a fully rebuilt distributor ready to put in when I can get better access, and I’ve set the points to exactly .012". Maybe when I put in the new radiator I’ll do it.
Chris
Chris, as you know there’s seemingly contradictory information regarding the correct points gap for the DVX6A distributors supplied to the XK120 and XK140. The Service Manual (on page B.63) says .012” while some of the Handbooks (on page 37) say .014”-.016”.
I’ve never found a clear explanation for the contradiction in XK literature, but I did find it in the Lucas Overseas Technical Correspondence Course. The answer is whether the points opening cam in the DVX6A distributor is the earlier “standard lift” version or the later “high lift” version. Here’s a photo of the cam I’m referring to.
Fortunately, I have several of these points opening cams in my spare parts collection so I was able to determine the identifying measurements. If you have the early standard lift cam, it will measure about .704” across the valleys and about .745” across the peaks. With this cam you set the points at .012”.
If you have the later high lift cam, it will measure about .686” across the valleys and about .742” across the peaks. With this cam you set the points at .014”-.016”.
The Service Manual on page P.4 provides the dwell angle, which is another way of determining the points gap. The dwell angle is 38 degrees plus or minus 4 degrees. Because the XK distributor is so difficult to access, a dwell meter is very helpful. I purchased a very nice used dwell meter on eBay for about $10.
From experience, I’ve found that a new points set will bed down about .001” after a few hundred miles. My distributor has the high lift cam, so I initially set the points at .016” which equates to about 34 degrees dwell. After a few hundred miles, the points will bed down, and the dwell will settle very close to 38 degrees.
If your distributor has the standard lift cam, you may find it advantageous to initially set a new points set at .013”. They will likely bed down slightly and settle at .012”. This assumes you are purchasing high quality points with a durable fiber rubbing block as supplied when these cars were new.
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Thanks for all this info, Mike - appreciate it! The distributor I’ve built up to replace the borrowed one currently in the car is a GC53 40372A date 2 56. I believe this was originally fitted to the Mk VII. I got the correct springs for an 8:1 XK120 from the Distributor Doctor here in the UK. The weights are the same, so essentially I now have an XK120 spec distributor. I also bought a new 408999 cam. The vacuum canister is a 7 18 12 419066 one. Maybe these vacuum advance figures ar not quite ideal for a B-Type head…? I notice that the cars equipped with the better breathing C-Type head (compared to the A-Type) use 4 23 12 canisters. I imagine the B-Type breathes much the same. I will measure the cam today to check what type of lift it has. I’ll also check the dwell on the engine as it is currently. I do have a fibre rubbing block on the new distributor.
Mike, I put the dwell meter on it today and it was miles out. It’s so awkward to get at the distributor in situ, and after many tries where I thought I’d got the gap right only to find it had widened after the clamping screws were tightened down, I finally thought I was somewhere near .011" gap. Wonder of wonders, the dwell meter was bang on 38 degs! The engine is running much more sweetly now, albeit with a very slight intermittent miss when revs are held steady - most noticeable between 1000rpm and 2000rpm. I’ll see how things are after I’ve driven it a bit. I’m goimg to get an inline plug tester and see if it shows up anything. Perhaps I should widen the plug gaps up from .023" to .025"…
So, thanks so much for your help on this!
Chris
Glad to hear you’re making progress. I find it impossible to service the distributor in place. I remove the front wheel, go in through the opening in the valance panel, and take out the distributor for service.
The DVX6A distributor clamp is terrible. It must have been designed for engines with the distributor on the opposite side. I recommend a simple modification to the clamp so the loosening/tightening nut faces outwards instead of inwards.
That may be true, the same part number was used for Land Rover Station Wagon and P4 75 Saloon.
Did you try changing the condenser (aka capacitor)?
That’s a good idea, Mike. I haven’t tried to remove the distributor at this time. I measured the lobes of the 408999 cam I’ve put into the spare distributor. I measured the lobes at 0.742" and the valleys at 0.696" (not 0.686") but maybe I measured this incorrectly? But, it does sound like the higher lift cam, I think…
I did change the condenser, Rob. Am I correct that it should make a good earth via the mounting clamp? My spare one is a bit of a loose fit in the original-style clamp, so I wrapped it up with a long strip of kitchen foil to make a tighter fit.
Chris
Yes, any way to get a good earth connection to the body. More modern ones have the clamp spot welded to the body.
Any of them will work fine. You can even mount them outside the distributor or on the coil and connect to the CB side terminal.
A condenser inside is two sheets of metal with a sheet of insulation between them, all wrapped around together, with one sheet connected to the body and the other to the center terminal. So they are essentially two parallel sheets separated by the thickness of the insulator. In science fields they are called parallel plate capacitors. Capacitance is the ability to hold a charge.
When they start to arc through the insulation, allow current to jump the gap, that’s when you get misfiring.
Bit of a breakthough yesterday. First, I tried checking the timing with my timing light. By some miracle, when I looked through the hole in the bellhousing, a white mark from someone’s last attempt at timing was there between two teeth! However, when I tried the timing light on it, not a trace of the white mark was to be seen. I tried using the rear (No 1) plug, and the front (No 6) plug - in case they’d timed it on that plug, but the white mark was not visible. I did notice that the ring gear teeth seemed to be oscillating back and forth a bit.
I then fiddled about trying to attach the new copper vacuum advance pipe, but gave up, as it’s just a bit too inaccessable from the top. I’d noticed that the car started more reluctantly than usual when I first fired it up, which surprised me, as I thought that problem was dealt with. When I tried starting it again, having warmed the engine up, it wouldn’t… not the remotest sign of it wanting to start, apart from a bit of a cough back through the carbs with a puff of smoke. Then I got to wondering… it seems like maybe the ignition might be retarded…? When I tried to turn the distributor I was very surprised that I could move it a bit just by hand, without even loosening the clamp nut. I nudged the distributor clockwise a bit to advance it, and it fired straight up, and has continued doing so! Eureka!!
I’ve just ordered a new clamp from a Series 1 Land Rover specialist, and will modify it to Mike’s design. With the original setup I couldn’t get a spanner on the nut from above to even be able to tighten it properly. Next step - remove the inner wing panel to gain better access. Any tricks to be aware of before I start? It looks like all the fasteners have recently been replaced. Of course, being RHD, the steering column will be a bit in the way!
Chris
Chris, maybe it’s different on.a RHD XK120. But on a LHD XK120, there’s no need to remove the valance panel to access the distributor. With the distributor clamp modified, there’s room to reach into the opening at the front of the valance panel and set timing. There’s also enough room to remove/replace the copper line to the vacuum advance or to remove/replace the distributor itself,
For what it’s worth, I’ve never used a timing light on my XK120. I just set the timing using the static timing method described in the Service Manual. However, after rebuilding the distributor I put it on a Sun Distributor Machine to verify that it would advance to the specifications shown in the Service Manual.
Mike,
when I tried to start the car today, it wouldn’t. I had to back it out of the lockup in gear on the starter. Sure enough, the distributor had retarded again! I advanced it a little bit more than last time, tried the timing light (on the rear spark plug) and found I could see two white timing marks, 2 teeth apart. I’m assuming the lower one (as you look at it) is 10 degs advanced, so that’s what I set it to, in the meantime.
When I’ve got the new clamp I’ll look at the best way of accessing the distributor. I might even take off the carbs, as I’m going to drill and tap each of the heat spacers to take a 2BA barbed fitting for connecting to my vacuum gauge - a great and easy way of setting the fuel mixture.
I’m also going to move all the plug leads one (maybe two) terminals clockwise so I can have the vacuum canister pointing in a better direction - it’s currently pointing almost at the engine block. Best to have it about parallel to the engine, I think.
Chris
Mike,
could you possibly give me the thread size of the extended nut, please? The Viart book doesn’t really mention the clamp at all. I assume the nut is 1/2"AF? I’ll get some hex bar and get a friend to drill and thread it on his lathe. Rather than weld the bolt I thought I might file a register for the square bolt head on the other side of the clamp.
Chris
Chris, the original bolt is 1/4 inch coarse thread. I don’t recall if it’s an Imperial thread or Whitworth. But the original nut being approximately 7/16 inch across flats is too wide to simply reverse the bolt.
The replacement is just a common hardware store 1/4 inch bolt and split lock washer. The nut is a generic 1/4 inch extended coupler because they are only 3/8 inch across flats and will turn within the register on the clamp. The extended length allows you to feel the nut with your fingers and to put a socket wrench on it.
Thanks, Mike. If it’s 1/4" UNC then a long coupler nut (I didn’t realise you could get such things!) would do the trick perfectly. Not having a welder, I’d like to use the original bolt with the square head and file a register on the inboard side of the clamp, then the existing register (now on the outboad side) could be relieved with the Dremel grinder or file enough to allow the nut to turn freely. You can even get a 1/4" x 20 stainless coupler nut.
Well, here’s my distributor clamp, modified as above to be able to tighten easily from the outboard side. Thanks for the inspiration from Mike Balch! I sourced a new distributor clamp from an outfit in Belgium which specialises in Land Rovers - Series Forever. It apparently fits early Land Rovers and Rover cars. It probably seems silly that I didn’t source one in the UK… The price was just over 11 Euros, but the postage was 19 Euros! It was quite easy to do, just measured and cut the register with a hacksaw, finishing it properly with a file. The bolt is 1/4" x 20 UNC, and I got a stainless coupler nut to fit that thread. Should work a treat!
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This is the E-Type version.
Re-inventing the wheel. 
Just got my distributor back from The Distributor Doctor today. I posted it just a week ago, and they got straight onto it the day it arrived. The next day I got a call to say it was finished! Now, that’s quick service! They replaced the lower bush, though I was unaware of any movement in the shaft that I could feel. Someone had fitted the driving dog 180 degs out, so that was put right. The advance springs were changed to bring it to bring it to XK150 8:1 equivalent (as I thought that was the nearest to my car, which has a B-Type head). Something inside the vacuum advance was replaced, one of their speciallly made red rotor arms fitted, and the distributor was checked on their test machine. It came with a copy of the new advance curve, which was within specs. Also, I was reminded not to use the condensor, but I have one of their specially-made ones on the car at present. Same went for the cap, but I had just sent it with an old one fitted for protection. The cost I thought was very reasonable, too. All in all, a very thorough job, and I have every confidence it will function perfectly!
Installed the rebuilt distributor today. I removed the front carb for better access, and also fitted the modified clamp (see above). Once I realised I’d moved the distributor leads the wrong way (car wouldn’t start) it fired straight up. Now silky smooth, with none of the misfire when revs held steady. Also fitted the copper vacuum advance tube (though not connected at carb end yet). Tomorrow I’ll dial in the timing. RESULT!!!
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