Distributor drive dacklash

[nigel jarrett]

Has anyone any idea how much backlash to expect in the distributor drive ,I have been setting the static timing and getting it correct is being hampered by what seeems a lot of free play , it's not in the dizzy or advance weights ,any thoughts please

[Keith Clements]

Probably the brass screw drive on the crankshaft. New ones used to be available. But check the fixing of the extension rod and circlip. On the coast to coast run across the USA we had this come apart.

[nigel jarrett]

Attachment of shaft and drive dog look ok when I extracted the dizzy so looks like a bit of a strip down required to inspect the drive gears

[David Morris]

Hi Nigel,

Have you had a look at the dog on the end of the long distributor drive shaft? This is quite small and can get worn, where it plugs into the socket on the top of the oil pump. It's an easy job to pull it out after unbolting the distributor, but remember the orientation when putting it back. If you are just feeling the backlash on the rotor arm, then this is controlled by the bob weights, so doesn't reflect the true shaft backlash?

Rather more complicated is the backlash on the oil pump drive gear when mating with the bronze skew drive gear wheel, or indeed the mating gear on the top of the oil pump itself. You would need to remove the front timing cover to get at both of these, as well as the timing chain and bottom wheel. If you find the bronze wheel to be worn as Keith says, and they do get quite worn, we have some in the spares shed, if that helps, as they were quite expensive. You can tell the wear by the gear teeth getting 'sharp' rather than wide and smooth when new. If the oil pump gear is worn, then I am afraid replacement is the best option. We can probably find you a spare.

If the gear wheels are worn, have a good look at the little oil jet mounted on the oil pump that is supposed to spray a jet of oil on the skew gear. It's part number is 52468. It can get blocked and I had a skew gear ruined by this problem!

Hope this helps,

David

[David Morris]

Hi Nigel,

Out of curiosity I asked Google to find the meaning of 'Dack'. Apparently, it's an Australian verb meaning 'to remove the trousers from someone by force'.

I was interested how this relates to distributor backlash in the UK, but perhaps our colleagues in Australia can enlighten us Poms?

All the best,

David

PS, We all need to smile occasionally in these Covid-19 times!

[nigel jarrett]

I have removed the dizzy and checked the drive dog and the shaft .There is little or no signs of wear ,with the dizzy fitted I removed the base plate so as I could watch the bob weights .The backlash I measured was approx 25-30 degrees before any movement of the weights .
This has all come to light now I am investigating the uneven tick over and also there is a bit off a chatter from the timing chain area which I have always thought to be a com follower

[David Morris]

Hi Nigel,

Hmm...sounds suspiciously like there is wear on the bronze oil pump drive gear, as Keith suspected. One test you could try is to repeat your test of the removing the base plate again. Insert the starting handle and watch when there is movement of the bob weights as you rock the handle back and forth. You should get the same 25-30 degree movement?

If so, it looks likely that there is wear on the skew gear or the oil pump drive gear or both? Perhaps someone else has some ideas?

You mention 'chatter' from the timing chain area. This could be a worn timing chain? Do you have an adjustable peg for the front of the camshaft? If so, you could try adjusting this, but ONLY WHEN THE ENGINE IS NOT ROTATING. Slacken off the lock nut, screw in the adjuster until it meets the camshaft face and back off by about half a flat on the lock nut. Holding the peg steady, lock up the nut.

Removing the front timing cover to check is not too frightening. There is, unfortunately, quite a lot to take off. The dynamo bottom bolt has to be removed, so too the water pump. You have to remove the starter dog, probably after locking the ring gear under the clutch, to 'freeze' the crankshaft. Then the bottom fan belt drive pulley slides off. Following this you take out all the front timing cover bolts, including those coming up from the front lip of the sump. Remove the two bolts holding the fuel pump onto the casting, probably no need to remove this as it just needs to clear the front cover. Unscrew the breather pipe from the vent valve. Then lift off the front cover.

Inspect the long 'teeth' on the skew gear. If you can see wear, there's your problem. The skew gear will need replacement. You should now mark the relative positions of the camshaft chain wheel and the bottom chain drive dog. Remove the camshaft chain wheel and slide the bottom drive dog off the crankshaft end. Follow this with the skew gear, it just slides off.

Replacement is the reverse of the above, just as the Haynes Manuals used to say! You can take the opportunity to replace the timing chain and you can check wear on this by holding it flat away from you. If it 'droops' by more than 1cm or so, you need a new one! One point to watch though, upon reassembly..don't tighten up too tight the five long bolts going through the front cover into the rear timing case cover, otherwise this will tend to 'tip' the rear cover forward, which could prompt a whole lot of other problems you don't want! You will probably need a new gasket. I expect JCS has them, but I find replacement gaskets shrink in storage, wherever you buy them. It's a bit time consuming but I tend to make my own from a sheet of gasket material, using the cover as a pattern. For the price of the material ( which in fact could be an old cereal carton ) and the right sized punch, you will have a gasket which fits perfectly. Use some gasket 'goo' sparingly.

Hope this helps,

David

[nigel jarrett]

Hi David thank you ,when I was trying to originally check the static timing ,turning the crank over would show up a big delay before the dizzy started to turn .So I will strip the front off and check the gear ,probably drop the sump and check the oil pump jet ,whilst the front is off I will take the camshaft out and inspect .I have a spin on oil filter kit to fit so I have to change from a Volux to a tecalimate oil filter casting ,
Thank you for your time and thoughts

[Keith Clements]

Just a warning about gasket material.
It is very important that the correct thickness of gasket is used. The clutch and gearbox gaskets are thin paper. The timing cover is a bit thicker but I think a cardboard carton might be too thick. I use Flexoid, a material that is not absorbent to oil or water. Try Google or ebay
I agree that bought or stored gaskets shrink.
I still have a full set of original gaskets that I use as a reference but not a pattern. I use a peening hammer to carefully mark the outline and holes, preferably on a 'scrap' component. I also have a set of punches for making clean holes. On long gaskets like the timing cover and clutch I locate the gasket with bolts as I move around.

[johnairey]

Nigel,
Just a thought, I believe your Javelin is an early one which may be fitted with a DKY distributor where the advance and retard works by rotating the distributor in the timing case, is the distributor free to rotate in the casting?

On the DKY distributor you have no definite earth you are relaying on a metal to metal running connection which could give you an intermittent earth. Might be worth checking out?

If you do take off the timing case to check the skew gear wear. As a comparison when I rebuilt my engine I fitted a new oil pump shaft and a new skew gear on checking the clearance between the teeth I found it was just pinching a six thou feeler. Photo on my Personal Album.

On refitting the timing case don't forget to RTV the keyway to prevent oil passing through. The timing case will take two standard oil seals if you feel its necessary. If you have definite leak past the oil seal you can fit a speedi sleeve it the pulley which will tighten up the seal by adding 20 thou to the diameter.

[David Morris]

Hi Nigel,

Great that you have had a good set of responses! My comment about using cereal packets as gasket material was slightly jovial but if you are interested, I find Scotts Original Porridge Oats use a nice thick cardboard that is a bit oily, I wouldn't use just any old packet!

I see that you are planning on changing the rear timing cover from the original Vokes filter housing to the later Tecalemit. I would be very cautious about this! You are straying into one of the worst design areas on the engine! I would start by doing a close comparison on the alignment of the three oil ways, perhaps by using some fairly thin paper and a pencil, to get a pencil rubbing from the block, the old housing and the later ones, to make sure they all align. Bear in mind there are at least five types of the later housings, which shows you how much Jowett's fiddled about with the design here. There have been lots of previous threads about the problems with the rear timing cover and it would be worth doing a search of the available recommendations. I don't know if anybody has successfully converted from the Volkes housing to the Tecalemit? Perhaps others can advise?

If you do decide to convert, my recommendation is to opt for the 'O' ring sealing ring solution, which again has been extensively described in the recent past. Happy to help with advice if needed?

All the best,

David

[nigel jarrett]

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Spent this afternoon removing the timing cover ,the skew gear is so worn it's starting to break up ,wouldn't be long before it gave up totally

[David Morris]

Hi Nigel,

Glad you found the problem! That skew gear is completely knackered! Do you want any help with a replacement?

By the way, the distributor drive gear doesn't look too healthy either? It might be time to consider replacing the oil pump as well? There are several types, as Jowett's got to grips with cases of oil starvation. If you do replace the pump with a later and adjustable version, I recommend checking that the control valve is working properly. We had one recently that looked OK, but was seized-up with rust inside. Also, on any pump, and especially your present one, check the little jet that lubricates the skew gear is clear. You don't want to do the job twice!

All the best,

David

[nigel jarrett]

Hi David ,I also thought the pump gear was looking worn ,I shall be dropping the sump and having a close look at that ,
At present I think I have another skew gear in the shed if I can find it .,but thank you for your offer that I will keep in mind.

[nigel jarrett]

[imgimg]][/img]oil pump stripped and the jet nozzle has been unblocked,the drive gear is pretty worn