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Bruce's D1
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thornebt
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September 16, 2018 - 10:32 am
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I have just bought a D1 that has covered only a few miles in the last nine years - about ten miles in total!  On my first run out it was OK for about ten miles but then started to stutter like it was running out of fuel before conking out when I slowed down.  I can get it started but it seems low on power and doesn't run well.  I think it is likely that the crankcase seals are shot from the bike being laid up for so long.

I would like to test the crankcase compression before I remove and strip the engine - just to be absolutely sure the seals are duff.  I did wonder if I could screw a fitting into the gearbox filler plug (maybe a drilled drain plug) and use my vacuum pump with gauge to do a leak test.  Or maybe a drilled rubber bung would be easier?  Alternatively if I used a bike pump it might be possible to hear any leak from the seals?

Does anyone know please the best way to test the crankcase compression?

Thank you.  Bruce.

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Mags 1
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September 17, 2018 - 1:07 am
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I've worked on domestic two stroke engines for decades, I use a squeeze bulb and sensitive pressure gauge where needed, big problem is to find time to effectively block off top of crankcase where barrel enters, as air gets past piston rings easily, plus inlet and outlet ports at the same time and include an air tight point where you can mount the tubing for the tool.

Most trade people decide whether machine is worth spending time and money on stripping right out to crankshaft out and renewing crank seals (as on cheap trimmers and saws etc.) a motorbike is different of course and definitely worth it, you get peace of mind once the job's done also and it's not so hard once you get into it.

Four now on the road and at least several in bits.

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thornebt
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September 17, 2018 - 2:14 pm
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Thanks very much for your reply Mags1.  That all makes perfect sense to me now.  I've decided my seals must be shot as the bike is down on power and chucking out smoke, so I'm definitely going to strip the engine down and sort it out.  All the parts seem reasonably priced at Bournemouth Bantams so I'm going to stick an order in with them.  Howard seems very helpful and quick at responding to my emails.  

Cheers.  Bruce.

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Mags 1
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September 17, 2018 - 10:00 pm
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You're welcome, often a leaking seal will allow gearbox oil to get into the combustion chamber, which is often the cause of very smokey engines that are hard to start etc.

Four now on the road and at least several in bits.

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Piquet
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September 17, 2018 - 10:23 pm
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thornebt said

I thought the first thing to do would be to put some new petroil in it and take it for a run. About ten miles from home it started to stutter and lost power. The clutch failed. I thought this would be a broken cable but it was the pushrod not returning. Luckily it was mostly downhill on the way home and I slowly got back to base.

I did a compression check on the cylinder and got 65psi which I think is almost certainly on the low side. I then decided to check the gearbox oil and found there was none in it!

If you are going to strip it, both primary drive side main bearings will need checking as they should be lubricated by gearbox oil on a '55 Bantam, likewise the oil seal could have suffered damage.

I'm not a complete idiot ............................................ some parts are missing.

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thornebt
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September 18, 2018 - 12:02 pm
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Thanks Piquet.  I guess if there is zero play in the bearings and they spin without any roughness then they should be fine?  Cheers.  Bruce.

 

Edit:  Just realised that I am stating the obvious!!!

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nickjaxe
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September 18, 2018 - 2:47 pm
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If you bearings seem ok keep em...bearings that are readily available can be poor quality.

It was a combination of shot seals and crankcase sealer leaking on mine letting oil into the combustion chamber.

My compression was down as well req a rebore and new piston...suppose I could have got away with just a new piston but its only £30 for a re-bore...its fresh then.

Nick.

My Bantam video              https://www.you.....jpOFmzRZRI

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thornebt
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October 21, 2018 - 9:57 am
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Whilst my D1 engine is apart I thought I would cure the wobble in my clutch basket by fitting a new bush.  It won't push into the clutch as it's slightly too big.  I think that if I leave it in the freezer overnight and heat the clutch with a heat gun then it will probably slide or tap in fine.  But I just wanted to check that this bush is supposed to be a tight fit in the clutch and not a revolving fit.  The old bush was certainly quite a sloppy fit!

What appears to be pitting of the bush in the photo is actually just where it's been in my freezer.

Is the spiral cut groove in the outside of the bush designed to transport oil along the bush please?  It seems so fine that I can't imagine any oil managing to squeeze down it!

Cheers.  Bruce.

 

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sunny
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October 21, 2018 - 2:00 pm
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i  think   you  will  find  oil  grovs   in    the  bush    will  almost   disaper    wen  you  cut  it  back the  steel  parts   that  sits  on it  also has grovs on  so  it  moovs   round    i  think   ,,   the   maxemum    end play  is     .  007 "         AND  betwen   the    two   a     max   radil   gap  is .,  001   for  most  brass  bushes

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Mags 1
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October 21, 2018 - 4:19 pm
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To work properly the Bantam clutch bushes have to be able to move freely on both gear shaft and clutch drum, if it jams then it's no longer working as it should.

Four now on the road and at least several in bits.

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thornebt
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October 21, 2018 - 5:01 pm
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I understood that I would need to ream the inside of the bush but I didn't realise I would have to reduce the overall diameter.  Can anyone advise on the best way to do this please?  Just some careful work with a fine wet and dry paper?  Maybe mount it in a chuck and sand it down that way?  I guess if it spins freely then that will probably be the 1 thou clearance I need.  

Or perhaps the bush has been made too large?  I have an option to return it and could buy a bush elsewhere.  That might be the best way to go and if the next bush is the same I can then reduce the overall diameter.

Any opinions to help me decide are much appreciated.

Cheers.  Bruce.

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thornebt
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October 21, 2018 - 5:19 pm
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After submitting the above post I decided that the best way forward is to return the bush.  I've bought another on Ebay for £15.99 with freepost and I'll see how that one fits.

Cheers.  Bruce.

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thornebt
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October 22, 2018 - 8:00 pm
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My gudgeon pin has a small amount of rock in it so I'm going to replace it.  I've read the technical article on the forum.  Can anyone tell me the best type of drill bit for the oil holes please?  Would it be Cobalt HSS?  There seem to be a lot of different types!  Cheers.  Bruce. 

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Mags 1
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October 22, 2018 - 8:33 pm
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The bush would be phosphor bronze, which isn't much harder than brass, just a good sharp bit needed, or are you hinting about drilling an extra hole/s in the rod too? Drill bush first then use a reamer to get to end size, which will tidy up the burr from the drill bit.

Just re-read, you drill the bush, not the gudgeon pin.

Four now on the road and at least several in bits.

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thornebt
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October 22, 2018 - 9:03 pm
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Mags 1 said
The bush would be phosphor bronze, which isn't much harder than brass, just a good sharp bit needed, or are you hinting about drilling an extra hole/s in the rod too? Drill bush first then use a reamer to get to end size, which will tidy up the burr from the drill bit.

Just re-read, you drill the bush, not the gudgeon pin.  

Thanks.  Yes, I'm just talking about drilling the holes in the bush.  Rather than sort through my box of drills for a good drill I thought I would buy a new drill bit and wanted to get the best one for the job.  Cheers.  Bruce.

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thornebt
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October 24, 2018 - 7:40 pm
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I'm pleased to say that I got another bush and it fits perfectly.  No play in it and it spins freely.  That makes life a lot easier!  Cheers.  Bruce.

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GlenAnderson
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October 28, 2018 - 2:02 am
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Any decent jobber bit will do, if it’s sharp. If you’re going to buy one specially, then Dormer or Presto are quality brands. 

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thornebt
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October 28, 2018 - 5:04 am
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Thanks for the recommendation.  Cheers.  Bruce.

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thornebt
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November 8, 2018 - 11:55 am
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I'm currently rebuilding my D1 engine.  A previous owner has replaced the condenser / points with an electronic ignition module.  From Google I can see that Atom won an award for this unit back in 1976 but it's no longer manufactured.  I'm quite happy with the unit as it works fine but I'm just wondering if I should have a spare unit in case it ever fails.

Can anyone give advice, please, on a suitable ignition unit that would be a fairly straightforward swap for the Atom one?  If it's not too expensive I'll buy one just in case I need it one day!

Cheers.  Bruce.

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thornebt
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November 8, 2018 - 2:19 pm
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My crankshaft is refusing to rotate when I screw my D1 crankcases back together.  I would say that it's having problems turning when there is a gap of 0.75mm between the crankcase halves.  I've temporarily removed the crankshaft shims to see if that makes any difference but it still locks up.

I'm guessing that the main bearings must be too close together i.e. not fully home in the crankcases but I'm really not sure as I didn't seem to have any problems installing them.  I realise now that I probably should have bolted the crankcases back together before installing the oil seals.  Has anyone any ideas please?

Cheers.  Bruce.

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