A10 RGS Replica

[r3sc]

Hi All,

I’m brand new to this forum so be gentle with me and be aware that my knowledge and experience with the British marques is still somewhat limited.

Anyway, it’s a bit of a story so if you’re sitting comfortably, I’ll begin.

About a year ago a good friend of mine decided he wanted a nice RGS replica, so without mentioning it to me he went out and paid a considerable amount of money for what can only be described as a very, very poor kit of badly selected parts which came in several large boxes and crates.

The quality of the parts left a lot to be desired and I was a little apprehensive when he asked me to build the engine but I went for it and built the engine using the parts provided and many more purchased on the way.

Anyway, I gave the completed engine back to him a number of months ago and left it with him to fit it into the frame along with all the running gear.

The process of getting it ready for commissioning was slow due to Covid but I finally went to get the engine running last week for the first time. Guess what? It won’t start!☹️

So, here’s a list of things that I’ve done.

1, At the time of rebuilding the engine I totally rebuilt the magneto and I have a healthy spark on both leads. The magneto has manual cable advance.
2, Totally stripped, ultrasonically cleaned and rebuilt the carb with new Amal parts where required.
3, The engine block is a thick base cast iron item which was honed and fitted with new Hepolite piston rings, gaps checked, all good.
4, Cylinder head is aluminium and is fitted with all new BSA valves, lapped in and checked with petrol, all good.
5, The crankcase/bottom end is allegedly a rebuilt unit and does look to be in good shape. It is fitted with the 67-357 spitfire cam.

So, I have good spark timed at full advance of 3/8”, the carb is a fresh rebuild, valve clearances are all set to correct specification and despite all that with hours of kicking, not even a glimmer of a fire.

I’ve exchanged the leads, tried it on easy start and double checked the ignition timing with no joy.

The only thing I can think of now is valve timing.

The engine number is DA10R 12*** and I know it has the 357 cam in it as I’ve seen the number on the end. The timing gears are crank- 22T, cam- 44T and idler- 49T and when I set it all up all the marks were aligned.

I seem to have good compression and good vacuum on the induction stroke but the only thing I can think of is that it’s not quite happening in the right place.

Main questions-
A, Are the valve timing figures for this cam 51, 68, 78 and 37?

B, If I fit my degree wheel to this motor and set the valve clearances to 0.0020”, do the timing figures relate to the valve just starting to open/close or is it when they are fully opened or closed?

C, Are there any different combinations of timing gears as the ones that are fitted to the engine could be the wrong ones as they were loose in a bag.

D, Am I missing something obvious? Is my lack of experience with British iron shining through?

Another annoying issue he has is that the gearbox, which is stamped with the RRT2 designation provides for the kickstart leaning forward towards the front end dramatically and this makes it very difficult to kick, but that’s another post!

Anyway, I hope you guys aren’t fed up of me already and that you can give me some pointers relating to the above.

Many thanks in advance.👍🏻

[Triton Thrasher]

Did you try some petrol in through the spark plug holes?

Did you try starting it fully advanced?  That’s where the strong sparks are.

51, 68, 78, 37 means inlet just starts to open 51 degrees before TDC at the end of the exhaust stroke and just closes 68 degrees after BDC during the compression stroke.  Exhaust just starts to open 78 degrees before BDC during the power stroke and just closes 37 degrees after TDC at the start of the intake stroke. 

I don’t know whether 51, 68, 78 and 37 are correct, but that’s what they mean.

[r3sc]

Hi,

Yes, I tried fuel down the plug holes and directly into the throat of the carb and I have to say, never at any time did the plugs look wet.

If I put my hand over the inlet tract with the carb off it does try to suck my hand in but no fuel seems to be getting to the motor. I’ve even checked if there had been a bung of rag left in the inlet but nothing.

I tried with full advance, no advance and every position in between and never even had a single puff or hint of a fire.

I’m stumped so now looking at the valve timing.

Regards.

[Triton Thrasher]

You didn’t time the ignition to 3/8” after TDC or do it rotating the engine backwards?

Such things do happen!

Blocked exhaust?

[berger]

I would take the rocker covers off and get a piston tdc on firing to see what's happening , put it on centre stand or block it up if it hasn't got one and use 4th gear and turn the back wheel forward and backwards checking for tappet clearance at tdc when points should then be well on the cam and fully open

[trevinoz]

Those figures for the valve timing are correct.
As to timing gears, the early long stroke gears are the same but with timing marks in different positions.
Check that the pilot circuit in the carby is clear, the engine won't start usually or will start after tickling and cut out quickly.
Your magneto may have a strong spark in the open but may not fire a plug under compression.
Good luck.

[Swarfcut]

The earlier Longstroke A7 uses timing gears which are identical in dimension and teeth numbers to your  later A series, but differ in the position of the timing marks. Search the Forum "Longstroke Timing Gears." So yes, remote possibility of wrong parts.

 Other possible ignition wise is that there is an error in the way the timing has been set, eg after top dead centre instead of before. With the piston coming up on compression to the specified position, either by degree disc or measurement, set the magneto to full advance with the points just breaking. Hold everything still and fit the magneto drive gear.  Look down the pick up hole, the slip ring brass segment seen will be for the pick up and lead to that cylinder on compression.

 Plenty on the Forum about pre -start preparation for new build engines, particularly ensuring the oil is circulating.

  Before taking it apart, a first try, put some oil down the plug holes and give it a good kick session to lubricate the bores, seal the rings and circulate oil to the crank bearings. Plugs in, magneto end cap off to avoid any unintended magneto earthing and a good dose of "Start Yer Bast**d"  If it fires, turn your attention to the fuel system. If not, a compression test will tell if the rings are working, modern Hepolites have been reported as not quite cutting the mustard.

  Depending on construction the kickstart quadrant can be moved round on the splines. Possible with pressed on construction, brazed up variants no chance.

 Swarfy.

[Triton Thrasher]

And re-check the ignition timing in case it slipped.

[trevinoz]

I wouldn't be pouring much oil down the plug hole, probably none. It may seal the rings temporarily but won't help with bedding them in, more harm than good.

[RichardL]

I think it may have been mentioned earlier that your points may be slipping when tightening  the magneto pinion driving nut. Once you've rotated the points to just open at 3/8" BTDC (or, maybe 11/32), you need to sneak up on tightening the nut while applying enough back pressure on the points carrier to prevent it from slipping due to the tightening. Once you've tightened the nut, you need to check the timing again. Assuming you are using fag paper between the points, insert the fag paper with the piston about 1 1/2" BTDC, now turn the engine over with the rear wheel or with a socket on the cush-drive nut just until the fag paper releases. Now, remeasure BTDC. As you are a newcomer to the process, I'd be very impressed (or embarrassed, recalling my own learning curve) if you got this right within about the first ten tries.

Here's an extra trick, attach an electrical clip lead to the fag paper and let the weight of the lead pull the fag paper out when the points open. Here's another trick, wedge a piece of pink eraser between the points carrier and the cam ring to create friction that prevents the points "bumper" (uuhh, don't know what else to call it) from running back down the slope of the cam ring.

Can't really say that this the cause of your grief (the bike not starting, not the grief of reading my ideas), but I hope it's useful, regardless. Also, as my Brit friends say, I hope this isn't teaching gramma  to suck eggs.

Richard L.   

[KiwiGF]

Hi,

Yes, I tried fuel down the plug holes and directly into the throat of the carb and I have to say, never at any time did the plugs look wet.

If I put my hand over the inlet tract with the carb off it does try to suck my hand in but no fuel seems to be getting to the motor. I’ve even checked if there had been a bung of rag left in the inlet but nothing.

I tried with full advance, no advance and every position in between and never even had a single puff or hint of a fire.

I’m stumped so now looking at the valve timing.

Regards.

Does the carb flood properly when you “tickle” it? (I am assuming you know the normal starting procedure)

If the carb floods and you have spark this should result in it firing at least (but keeping it going after firing is another part of the puzzle)

[Swarfcut]

 Trev. Good point there, not too much oil, just enough to produce decent compression. But to be honest I'd worry more about getting it to fire and run.

 AAHThree.     Its back to basics, mechanical, ignition, fuel. Easy fix if you work through it in a methodical manner. We've all been down this road, I reckon Richard has pointed the way. When fitting the magneto drive gear, make sure the tapers are dry, push it on and then give it a  very light tap to hold the two tapers together. Then hold things still and sneak up on that retaining bolt. Yes, it is a case of being very lucky to get it right first time.

 Swarfy.

 
 
 

 

[r3sc]

Hi Guys,

Many thanks for all your input. I’ll try to answer all your queries in turn.

When I rebuilt the engine all internal components including bores etc did get a liberal coating of oil so I’m happy they are well lubricated.

Yes, when I tickle the carb there is flooding and all looks to be ok. The carb did spend at least an hour in the ultrasonic cleaning tank at time of rebuild and I’ve re stripped it and double checked for any blockages.

I’ve checked and double checked the timing. I’ve turned the motor over using the back wheel in 4th gear until it’s at TDC then turned it backwards and measured the downstroke at 3/8”. Then pushed the timing gear onto the magneto shaft just as the points were about to open. I’ve been very careful about tightening the magneto nut over the square section spring washer to ensure it doesn’t turn during tightening. I’ve since double checked this a number of times.

Exhaust system is brand new.

In my head, if any of these things were wrong I would at least get a fart or a backfire, but there’s nothing. No sign of life at all.

After using easy start down the throat of the carb, still nothing so I think that eliminates fuel.

The Unknown’s for me are as mentioned, a break down of the magneto output under compression pressure or valve timing and at the moment my money is on valve timing.

Sadly I can’t get access to the bike for a couple of weeks as my mate is on holiday but I want to be fully armed with options for when he gets back.

Once again, thanks for the input, everything is welcome!

Regards

[Swarfcut]

AAHThree. The way you set the timing position may be significant. Rotating the engine forward means the timing gears are moving under load and backlash is eliminated. Try rotating forward, finger over the plug hole to feel the compression build, insert your measuring stick and stop when the marks show the piston correctly positioned. Now turn the timing gears backwards by turning the cam drive gear to ensure the gear train is loaded as in normal running. Set the mag at full advance, points breaking, and fit the drive gear.

 Late model piston height, A10 SR (GA frame prefix, so assume 357 cam) is given as 13/32" BTDC.

 Swarfy.

[r3sc]

Hi Swarfy,

Thanks for that. I’ll certainly try that ASAP.

With regards to pistons, I’m not sure what they are but I think they are oversize. The cam is definitely the 357 item.

I’ve included an image of the pistons prior to ringing and fitting of the barrel and wondered if you could comment as to whether they are the right ones in terms of compression ratio to suit the 357 cam and the timing figure you suggested?

Regards.