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#815671 07/09/20 7:36 pm
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Hi all,

Hope you can help me. I just did a complete tear-down on my 1958 Ariel Square Four since it had not been running for a long time (save around my neighborhood after I bought it). Good thing I did dismantle it as I found a broken stud banging around in a push-rod tunnel and that the crankshaft oil ways were filled with concretions. Anyway, after the rebuild, I cannot get it to start. The cylinders were in spec, so I just honed them and installed new piston rings. but there was not even a splutter with each kick. I have a healthy spark (standard points and distributor) in all 4 plugs.
There is very poor compression - only about 50 psi - in each cylinder! I rechecked tappet clearance and all have appropriate gaps. I have not done a leak down test, yet, as I do not think it’ll answer the question at this point.

The first thing that comes to mind is that I have the valve timing all wrong. The odd thing is that the crankshaft pinion has three keyway slots at 120 degree intervals. The book says this is “in case alternative timing is required” Seems peculiar to me. Anyway, there are supposed to be two lines on the pinion that should point towards the camshaft when the appropriate slot is chosen. Mine only has a punch mark and I chose that to set the timing with. Is it likely that this is incorrect and that I should try timing with an alternative slot? If not, what other things should I try, short of removing the head, again?

I look forward to all responses and thank you in advance,

Paul.


Paul

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This is from the 1949-51 owner's manual. I hope it helps.

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Thanks, Magnetoman. I have the same manual and followed those instructions. Do you happen to know the valve lash settings at which to determine the valve opening timing, please?
Paul.


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I would double check the installation of the distributer. I have not done a Square Four in a while but remember getting it wrong on more than one Square four.

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Well, I’m still in the same situation - absolutely no hint of a pop, burp, bang even with roller starter.
So, back to drawing board:
1. Carb - completely dismantled it again and cleaned and polished the slide as it had been sticky from the resting position. All new seals and jets perfectly clean.
2. Spark - all four plugs (new, of course) have spark. Re-timed according to book and described above
3. Cam timing - with indicator dial over #1 inlet valve and tappet clearance at zero, confirmed that peak pushrod rise occurred at 105 deg ATDC (actual reading in my case was 106 deg.)
4. Crankshaft position - yes, Numbers 1 and 3 rise together as 2 and 4 fall together.

I’m flummoxed!


Paul

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i once timed my square four with the points opening on the wrong side of the opening cam . I was actually on the closing side of the cam points cam . needless to say it didnt even splutter . once i realised my mistake and put it right it fired first kick .

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Hi Paul,
It sounds like you have the cam timing sorted ?
To check the ignition timing
Bring no 1 cylinder up to TDC on compression stroke, use your thumb to feel the compression on the way
remove the distributor cap and check that the rotor is pointing to no 1 on the cap, at the same time the points should have just opened or open when you turn the rotor a little against the direction of rotation

Compression seems low at 50 PSI, did you fit new rings?
add a small squirt of engine oil to the cylinders and see if it rises significantly

John

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Agree with Paul above. 50 psi is not enough compression. At sea level your air pressure (weight of the air on top of your head) is 14.7 psi. At 50 you are getting about 3.4 to 1 compression. Only starter fluid would ignite in that situation. (disclaimer, DO NOT USE STARTER FLUID)


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With a hone and new rings, they won't be seated yet, so the (cold) compression will be low.
CAREFUL application of starter fluid should be OK, but doesn't sound like the problem ?

Always keep an extinguisher handy ...

Can you visually observe that the spark is occurring around tdc, on the COMPRESSION stroke ?
Have you tried a teaspoonful of neat petrol (gas) down a plughole or 2 ?
Or given it a good tickle or pulled on full choke.

Still keep that extinguisher handy.
And do this outside ...

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Originally Posted by The Bonneville Shop
you are getting about 3.4 to 1 compression. Only starter fluid would ignite in that situation.
Sorry, but not quite factual. Model T fords run and start on cheap gasoline just fine with 3.5 to 1 or 4 to 1 compression ratio.

Also, calculating a compression ratio by dividing a gauge reading by 14.7 doesn't provide a true idea because most intake valves close after the piston has traveled back up the cylinder a certain number of degrees. Even the aforementioned model T intake closes at 50 deg ABDC. Your calculation assumes an intake closing at exactly bottom dead center.

But now for a few basic questions for Paul. Did you hold the throttle wide open when checking compression? You must do that otherwise a low reading will result. (And, prop the slide open if you have a SU carburetor.)

Next, is your gasoline fresh? Is it clean and free of water? Do you smell gasoline after trying to start it? (Sniff the exhaust pipes too.)

Then, how hot is your spark? Will it jump a 1/4" gap?

Is ignition timing close enough to fire up? The finger in the plug hole test while watching for spark is really useful. Pull all the plugs, hook them up and lay them on the engine. Cover a plug hole with your finger and kick the bike over. The compression will blow your finger off of the plug hole and at that moment, that cylinder's plug should spark. You might need to do it a few times to get the rhythm down but it is an excellent quick check to see if ignition timing is reasonably close, and......to see if the firing order is good.

If you have all this, it should do something, especially on a roller starter.

Last edited by Stuart Kirk; 11/17/20 12:22 am. Reason: More info
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Originally Posted by Paul Sammut
Well, I’m still in the same situation - absolutely no hint of a pop, burp, bang even with roller starter.
So, back to drawing board:
1. Carb - completely dismantled it again and cleaned and polished the slide as it had been sticky from the resting position.
Your comment about sticky carb slide (piston). It sounds like you have an SU carb which would be correct for your bike. If so, that "slide" (variable venturi) will stick down in the "closed" position if the jet is not centralized to the needle. This is common on a carb that has been reassembled without the centralizing tool and is no good and must be rectified. There is an SU tool kit available that has a piloting fitting to help you get that jet guide centered so the slide (piston) can move freely. It can be done without the tool but it is not easy.

Next critical setting is jet height. You are surely well aware of the 3/8 BS nut and it's spring on the bottom of the carb for adjusting mixture strength. That nut's job is to raise and lower the needle jet. That jet is almost always sub flush to the "bridge" (the flat section the slide sets atop of when closed). For initial startup on these carbs, I usually adjust that jet so it is .070" to .090" sub flush to the bridge measured with a digital caliper. If the jet is flush, the needle basically plugs up (or severely reduces) the only source of fuel the engine has. Once running, adjust mixture as needed.

Finally, there is float level. With carb mounted on the engine and the top and piston removed, turn the fuel on and visually check how far the fuel rises up in the jet. You should be able to see it but it absolutely should not well up so it spreads across the bridge and overflows. And it shouldn't rise any higher that the top of the jet which is sub flush to the bridge. Remove the float bowl cover and adjust the little forked lever and check again until you are satisfied with the level. This is the only way I ever set float level on SU's anymore.

I realize this is a lot of tightly packed information to digest but hopefully it will help. And there is more. Don't hesitate to ask if you need clarification.

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You really should be tipping some neat petrol down the carb throat or plughole(s) and seeing if you can get some pops or bangs out of it.
Or even a short burst of life.

If it does nothing of the sort, then its not petrol related, and the problems lie elsewhere.
Spark timed on the compression stroke. ?
If its timed on the exhaust stroke, it will never go anywhere...

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I had a low compression problem on my Lightning newly bored. Put some oil in both cylinders which made it a bit difficult to kick put it did then fire.
Ran it for a while to break in and now it starts fine. Have not yet rechecked compression.


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Oh my goodness - my apologies, guys! I forgot about this thread and haven't looked at it for ages. You all have been very kind with helpful responses and I haven't read them until now.
I managed to get the bike started after many frustrating attempts - and I'm embarrassed to say I never updated you.

The problem was with ignition timing - and I still don't completely understand why.
My distributer's rotor arm has a "hooked" brass contact with a fairly long extension, or hook. That part comes in contact with the cap's brush first, so I assumed I should time it at that point. As it turns out, I was wrong and had to time it significantly more retarded.

Anyway, it didn't run for very long before I realized that the dynamo wasn't charging and that every time I placed the bike on the side stand it leaked oil heavily - from the left footpeg!!?? I found that the oil seal in the dynamo was rock hard and had a chunk missing and my dynamo internals were bathed in oil. The oil then poured out of the dynamo's chrome cap and onto the footage anchoring point and ran down the peg's extension through the timing cover and down to the floor well beyond the timing case. Cleaning the dynamo out carefully and replacing the seal weren't enough to get it charging again, so I opted to get the alternator conversion from Iron Horse Spares which I am awaiting. Meanwhile, I have converted from 6 volt positive earth to 12 volt negative earth in preparation for the new kit.

I also converted to electronic ignition and this has a more conventional rotor arm supplied with it. I will let you know how the conversion goes.

Paul.


Paul

'74 Commando - Interstate
"74 Commando - Hi-Rider, possibly
'65 Atlas, mostly anyway
'15 R1200 GS Adv
'51 Vincent Rapide
'58 Ariel Square Four

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