Pushrod question - problems starting new engine

[chaterlea25]

Hi Duncan,
Try a colourtune plug in the dead cylinder, that way you can see if its firing under compression
if not its the mag,
otherwise its a mechanical problem, I had a similar prob with a bike some time ago turned out to be a very soft valve spring,
it would close the valve kicking over but not with the engine running (sticlky or slightly bent valve may give the same symptoms)

HTH
John O R

[Alan @Ncl]

Duncan.  Something worried me in your post when you said both inlets seemed open together?  I can' see anyway this should happen.  Sure the inlet and exhaust are  open together briefly during the scavenge period over TDC at start of Induction stroke but the other cylinder is on its power stroke so its inlet should be closed. 

Can you get a bit of tight-fit flexi hose in the plughole and blow into the two cylinders on the two TDC positions.  If one cylinder can't give you resistance, you know there is a problem.

Alan

[bsa-bill]

Yes Alan that struck me as not quite right so I've just been down the shed (damn it's cold in there), I already had the rocker covers of so took out plugs and slowly turned it over, Duncan there is no point where both inlet valves are on the move together, one should get right home before you can see the other move, looks like maybe the sticky valve is a good possibility .
I had a similar thing with my exhaust valves one was a bit sticky, it would just stay down for a little while and then flick up, possible this is happening to your inlet.

Also tried out the Chow Mien compression tester, ummm first off the Krypton factor bit, amazing number of bits to screw/plug together ( is this correct ) then I got nothing, I probable have not got it all screwed up tight enough and the cold was getting to me, I'll try it again later when the heaters on.

[Duncan R]

Thanks for all your replies again,

I tried another compression test with the throttle wide open and got 30 psi on the right and zero on the left.

I then decided to take the rockerbox off. With the plugs still in I cupped my hands over the valves and kicked the engine over, I could feel air coming up past both exhaust valves - surely this is not right as both valves should be firmly closed? I have now taken the head off and filled the combustion chambers with white spirit to see if it leaks out.

Bill,

With that tester I used the adaptor with the single thread and connected the gauage direct to it and nipped it up with a plug spanner.

Cheers all

[bsa-bill]

I managed to get 30 lbs/in on the tester, changed the adaptor and got zero again, I'll have another look to see if I've got it set up wrong
Fixed up my old tester ( should have done this in the first place ) and got 90 in my slippers
I think maybe 30 on the new one might equate to 90 really, I'm not too sure about the thing, will give it a more thorough test if and when time allows.

When you say you cupped your hands over both valves do you mean over the valve springs or over the exhaust outlet.
If over the valve springs remember that there are two drain holes, one in each exhaust valve rocker compartment of the head, with the rocker box off this is possibly the easiest route out for air from the sump as you kick it over rather than forced through the breather (could be wrong here though), I'm thinking a valve would have to be pretty bad to cause no compression other than it not closing completely, the leak test will show something one way or another

Can be frustrating all this, but I've never heard of anyone selling one because it never started, and you know yours does go

[andy2565]

have you considered a leakdown tester if you suspect the valves,instead of measuring the compression it actually tells you where its leaking,all cylinders are exspected to loose up to 15% of compression past the rings,google it and its well worth it,i made one and its a must for twins as you can work out exactley where its leaking,try this website http://www.650motorcycles.com/LeakDownTester.html

[Duncan R]

Thanks Bill and Andy,

Well Bill looks like that compression tester is of pretty poor quality, those readings are similar if not exactly what I am getting. Just checked the head and I have white spirit dribbling out of the inlet manifold. Looks like I need to get myself a valve spring compressor and check the valves and seats.

Thanks Andy for the link, I will have a look.

Anyone know the lenghths of the pushrods? I don't trust any of the parts in this engine after what was found in the bottom end

Cheers

Duncan

[andy2565]

yes sounds like something is'nt seating properly,once you have it assembled again give the leak down a try just to m,ake sure both cylinders are the same,there's loads of sites that show you how to make one and explain how to use it.i'm stuck with my rebuild at the moment,i bought a 1549 head from the US and it needs all the valve seats doing,and its an expence i wasnt expecting,the guy next door is a pub technician and i built my leak down guage for nothing and one for my mate to,cant post pictures from this computer,as my miss's works on the main one,and she doesnt trust me on hers,waht with my oily hands and all.

[Duncan R]

Thanks Andy,

I will have a surf for the tester. I will get a valve compressor tomorrow and check the valves and seats out. hopefully I can get away with just lapping them in, I could also take the head to the local brit bike shop and let them cast their eye over it. This is eating money,what with having to buy extra tools and finding all the other faults, I do hope this is the problem as I can't really afford to have the mag done as well at the moment.

[Duncan R]

Dropped the valves out today - they don't look too bad, no obvious damage to the seats either,just need to lap them in now. I have ordered new springs as well. Not sure how you can tell if they are weak or not,but I can almost compress them with one hand, feel a bit weedy to me.



Cheers

Duncan

[iansoady]

If they're that soft they're definitely too weak. Valve springs are cheap enough - I'd just replace them.

Although TBH they don't do an awful lot when starting - weak springs generally show up at higher revs when you get valve float.

You'll get there eventually!

[Duncan R]

Hi Ian,

I have ordered a new set, as you say they are quite cheap so may as well change them whilst they are off. I will finish lapping the other 2 valves tomorrow and put some white spirit in the chambers again to check for leaks, it was just one inlet valve that was leaking. Not much point in me making a leak down tester as I don't have a compressor. Good opatunity to get an accurate timing setting with the head off as well. If its no go after this the mag wil have to go off for testing, because there is nothing else!

[a101960]

And while you are at it mark the timed breather and also make a mark on the timing case casting. The breather runs at engine speed. If you do this you will be able to time the engine in future by removing the timing cover and set the timing by simply lining up the marks.

John

[trevinoz]

John,
           I don't think that the breather runs at engine speed.
How about half?   [And I don't mean that I am going to shout you a beer!]
  Trev.

[Duncan R]

Thanks for the tip John.

Trev, does it run off the camshaft? I always understood that the camshaft runs at half crank speed.

Cheers

Duncan