Comet Help Please!

[miked]

I had a fustrating day trying to get my Comet together in time for a debut at 1000 bikes, and as a result my job list is now longer... plus I have a few questions I'm hoping I can get help with.

1. Timing gear end float - I have fitted a new large timing gear I have everything as per the parts book (ET173 & ET173/1), yet when I tighten up the steady plate I am seeing a lot of end float (about 1mm - sorry I think in metric...) - Is this normal?

There's also a little float in the small idler and Cam pinion, but nothing like as much.

2. Valve Timing - I lined up all the marks as per the Richardson red book, but something doesn't seem quite right. My inlet valve appears to be at least partly open on the compression stroke, closing just before TDC.
I'm presuming the marks are arranged to coincide with the firing stroke as the next time TDC comes around the exhaust is closing as you would expect on the exhaust stroke.

I'm a bit confused as there appears to be at least some compression - any thoughts?

3. Timing cover - The timing cover that came with my machine (it wasn't fitted as the P.O. had started the Timing gear job) has 4 oiling ports. 2 have seals in them, the other 2 are machined and drilled but don't appear to align with anything.
Would I be correct to assume this is a twin part? (the code isn't the same as the crankcases) I noticed there is a Comet part currently on ebay and while the port bosses are cast, but they don't look machined. So, are they the same castings, but with extra machining on the twin? If so is there an easy way to block the gallery to the 2 redundant ports or would I be wise to try and get the ebay one?

4. Oiling Quill - I can see how it fits into the timing case, but I can't see how it seals to the crank - its a very sloppy fit.

This is my first Vincent project and to be honest I'm starting to feel a little out of my depth, but I'm hoping with a little advice I can still complete it in time.

Many thanks in advance,

Mike

 

[Howard]

I think you'd benefit from a visit to your local section meet, these things are much easier to discuss face to face.

1. Timing wheels - some will tell you the exact end float, I tend to do it by feel. If the spindles have been replaced they may have been installed slightly out of position - I've seen much worse than 1mm variation. I try to get the gears in full mesh by using extra washers in the parts list (I don't know the part Nos) then 2 or 3 thou end float - there's only one thickness of washer so the end float is what it is - one washer less than too tight. The next thing is to shim the followers to make sure they bear on the full width of the cams - this is easier because you can machine the spacers to give the right end float if necessary.

2. Sounds like your timing marks are all to cock - not uncommon! Have a look round the tech help forum here, there's been lots of chat about valve timing recently.

3. Sounds like you've got a twin timing cover. I've never tried putting one on a Comet. I'd be inclined to use a Comet one and sell your twin one - you might make a profit.

4. Big end isn't sealed, it's a very low pressure system. Again, there's been chat about oil feed to big ends here recently that may be useful to you.

Good Luck, we've all been there, Vins aren't always like other engines.

H

 

[davidd]

I would just add a few comments to Howard's good advice. My experience with the timing gear endfloat is that you neet a wide selection of shims, regardless of the advice of Mr. Richardson or the Spares List. As long as your followers are hitting the cam correctly, you can shim the big and small idlers for best meshing and then endfloat.

If you did not build the engine originally, I would not rely on the marks on the gears. Much like the timing cover, the gear wheels are interchangeable on twins and singles and as you may know, the rear cam in the twin is the cam in the Comet. The marks would be different in these applications, so many gears have marks on both sides and the gear was pressed on for the rear cam on the twin or the (front) cam on a Comet. In addition, the gear wheel could be pressed on randomly, making the markings useless. In general, it is best to check and see when the intake opens, if you know the cam spec.

You are not correct about the timing marks being aligned on the compression stroke, although I would have thought the same as you. They are aligned on the exhaust stroke, more specifically, at 4 degrees BTD exhaust. This is what the illustration in Richardson's is showing. This is also where the intake and exhaust valves happen to be at exactly the same height. So, if you do not know what the cam is, it is best to set the cam based on this equal lift. As you may know, the marks on the gears only line up once and as the engine turns they will not line up on the next cycle, so you have to turn the engine backward if you are trying to use the marks when checking the valvle timing.

Finally, it seems that you have a twin timing cover. The aft holes are generally not machined on a Comet. I would not hesitate to use the cover, but I would close up the aft holes. There may be others that have done this using perfectly good methods, but my preferred method is to circle the hole with a small punch until it is closed. It does not have to be oil tight, but it is nice to have the oil going where it is supposed to instead of flowing unrestricted into the timing chest and robbing your cam of its fair share of oil. I am otherwise not a fan of peening, but in this case it prevents the use of goop, discs, screws, etc., that may fall out and cause worse problems. On each cylinder, one hole supplies oil to the cam and one supplies oil to the cylinder. On the twin all four are machined on the Comet only the front two.

David

 

[deejay499]

The cam wheel should have two sets of dots, one single not used on a Comet and double dots that match the ones on the main idler. Check to ensure you have matched the correct ones. Good luck. DJ

 

[timetraveller]

Do not trust the dots on any engine unless you know that they are correct for the cams fitted. Once timed and checked the dots can be used but if replacement cams have been pushed in the cams could be anywhere in relation to the dots. There has recently been much discussion on valve timing in these pages.

 

[Howard]

Hi Mike,

I think we've forgotten about fitting over the years. These engines were hand built by craftsmen, because they couldn't be put together by unskilled workers.

This applies even more with old, much "renovated" engines. You can't just buy all the parts listed in the spares list and put them together, it takes an understanding of the way the specific parts work and how gears, bearings etc work in general.

The best advice I can give, is to know your limitations (and your equipment limitations) and talk jobs through with people who've done them, before putting spanner to nut, it may save you from making the same mistakes they've (we've) made. After nearly 40 years of Vincenteering and more than 40 years in engineering I'm still occasionally surprised by features in the Vin engine - or at least how they work, compared with how I'd assumed they'd worked.

Hope to see you at Mallory - I'll be the one with the timing chest that sounds like Santa's Elves making toys for Xmas - or do they all sound like that?

H

 

[miked]

Thanks for all the great advice, a massive help - its given me a lot more confidence...
I agree totally with your last point Howard, and I’m only too aware of my limitations hence why I’m so grateful for the help and advice I get on here...
I’d rather learn “on the job” than have the work done for me and be no better off unless I can help it - in any case I doubt I could find anyone that would take it on in time to meet my target at this late stage.

I think with David’s figures I feel happy enough to tackle the valve timing, obviously I need extra shims for the timing wheel and that sounds relatively straight forward. I’m on to the ebay cover, but if it doesn’t come my way then I’ve learned the twin one I have can be modified (unless anyone has one they'd like to swap). I’ve then to set the mag, which I’ve done several times on my Norton (one less cylinder here though...), so hopefully I should be more or less good to go.
The carb is the next unknown quantity, so expect a raft of questions on that subject in the near future!

I’d love to get to a section meet at some point. Coventry would be my nearest – it would still be over an hour each way, but I should make the effort at least once a month. I’ll also have trawl back through the posts on here as well and see what else I can find to help.

Many thanks once again for all the contributions, they are very much appreciated.

Cheers
Mike

 

[b'knighted]

The recesses in the timing chest used to be fitted with restrictor discs to reduce the oil flow and while these were held in by the rubber washers something similar could be made thicker and held in by a gentle punch locking. They could even be made dished and flattened into the holes like the core plugs used on water cooled iron engines. This should hold them with no problems and cause no damage to the timing chest.
If you read all the advice given to others on these forums you will find a reading/reference list comprising
Riders handbook, Richardson, exploded parts list and Know Thy Beast. These will cover all of the basics although other books will be recommended for following the history of the machines and of popular modifications.
As well as searching the forums go to "The Main Club Site" link above and check Info - technical and Members - Articles - Whitakerpedia.

Only an hour to a Coventry section meeting, I'm sure you'll find it worthwhile. I was corresponding with RedRyder in Plano, Texas and he pointed out that his section meeting was moonshot away.
Cheers,

 

[Albervin]

The members living furthest away from the Section meeting place here in NSW would take over 10 hours to drive the distance. A couple of the guys have planes but landing costs in Sydney are ridiculous. You people in the UK don't realise how lucky you are when it comes to service and socialising! An hour to Coventry? We can only be jealous.

 

[BigEd]

Dear Mike,
The Coventry section would be pleased to see you anytime at our regular Friday night meetings at Berkswell. Let me know if you would like more details on how to find us. I can add you to our section email list if you like so that you are updated on forthcoming events, etc. You could also have a look at our website: http://coventryvoc.co.uk

]I’d love to get to a section meet at some point. Coventry would be my nearest – it would still be over an hour each way, but I should make the effort at least once a month. I’ll also have trawl back through the posts on here as well and see what else I can find to help.[/SIZE][/FONT]

Many thanks once again for all the contributions, they are very much appreciated.

Cheers
Mike