Ignition timing with today's fuel

Use the standard setting,unless someone has fitted HC pistons which will need less advance. Overheating is more likely to be caused by unequal timing on the cylinders, check with a strobe on both sides,and try a bigger main jet. Also check compressions are equal, a bad ex seat will overheat the motor too.

The way to get the timing right is to advance it until the engine pings while pulling away up hill, and then retard it just enough to stop the pinging. It would be hard to correct unequal timing between the cylinders, since this would require removing metal from the "Cam" in the magneto, but it might be worth checking anyway.

Older Land Rovers have easily adjustible ignition timing settings for different octane petrol. The lower the octane, the less advanced the ignition. There is a good reason for that. Modern petrol is considerably lower octane than was available in the 60s and 70s. The ratings are also calculated differently, so what is called 97 octane now was probably 94 octane previously, if that. From my own experience, I found that retarding the ignition 3 degrees makes a big difference - no pinking, no overheating, but no noticable performance loss. I would strongly suggest going from 32 degrees to 29 (Domi 99) for the sake of your pistons. I have just spent ages rebuilding my son's 88 which he rode hard on a summer's day on the autobahn 2 up on unleaded petrol. He didn't notice the piston crowns melting until the huge bang... The engine now has a compression plate and is set to 1/4" btdc rather than 5/16. Hopefully it is a bit safer now. Symmetrical ignition timing is essential. You can spend hours with a grindstone getting it right (as I have done) or just buy a new cam ring.

Interesting but not helpful. What, not even the bits about the Norton 88 I recenty rebuilt? I would again strongly suggest retarding the ignition 3 degrees from standard. It works for me...

Gordon.

Todays regular UL with 5% eth is reputed to burn faster than leaded,but also seems much less volatile than leaded,in any event ,so much has changed that you are on your own now. I buy any fuel that does not contain eth to lessen tank rusting and early decomposition. I find Shell top grade to cause plug fouling when the std grade (with eth) does not!!. I understand that the BP top grade has no eth but with the Millions BP has invested in ETH plant that may change .

John's idea of "getting it right first time" is desirable but rarely possible. In all old car manuals, certainly until the late 1970s you had an initialsetting and had to adjust the final setting by ear after a road test. Put the engine under heavy load and if it 'pinks' retard it a touch. (That's the short version!) Quite easy with the knurled adjuster type fitted to many car distributors. There are too many variables in an engine - especially a rebuilt one - to guarantee a spot-on setting first time! When I first overhauled my 99 I followed the Norton manual religiously and found that the bike would pink if I used anything less than 101 Octane! Yes, it needed retarding a touch! I guess the old 88 has a magneto? Because of the probs I had with my first 99 rebuild I swapped the coil ignition for my old K2F magneto (with auto-advance) from a 1955 88. It went well! I still ahve it but will put the dirtributor back for authenticity once it's been 'fettled'.

If it's much too advanced or retarded it will overheat and melt the pistons! I used to have one in my "Black Museum"! Somehwre I've got anothe one from a 3.8 Mark 10 Jaguar.

Cheers, Lionel

Hi John, Loss of comp when hot is often due to valve guides not having enough clearance on the valve stem causing the valve to stick open a little, were the guides renewed or sleeved?,are the rockers stiff ? oil supply can be poor, run the motor with the Ex cover off to see. What cam is fitted??.

If the compression has been raised over standard you MUST retard the ignition a few degrees to compensate (the flame has less distance to travel). Your symptoms are typical of insufficient clearance between the valve stem and the valve guide. This often occurs when a cylinder head has been overhauled and shiny new valve guides have been fitted. Check the clearance - particularly the exhaust valve guides. You may have to ream out the valve guides by a couple of thou.

John Shorter previously wrote on Saturday January 21st 2012, at 11.47hrs:

(Snip)

Anyway, my next step will be to increase valve clearances. If that does not work, I guess I'll have to take the head off again. I currently live in Spain where, unfortunately, there is no local expertise for old British bikes.

Hello John,

The suggestions you have had regarding 'power-timing' are sound.

Shame there is no obvious fault, but I hope I won't be confusing the issue with the following comments.

The most common reasons for overheating I have dealt with are lean running, either from under-jetting, blocked pilot circuit (weakening the mixture at part-throttle), or manifold air leaks.

Oh, and applying 1/8" of Cylinder Black on the barrels or head will warm things up a fair bit too.

The other cause can be from retarded (late) ignition, leaving the charge still burning as the exhaust valve opens. So don't have it backed off too far.

I don't know what was done to your mag when it was reconditioned. Also, while not wishing to imply that whoever did the work may not havedone it to a good standard, it's worth remembering that new components (condensors for example) can fail or start to deteriorate after a very short life, if they happen to be faultyout of the box. Losing power when the motor is up to temperature is a classic faulty-mag symptom.

Very, very rarely in the past I have serviceda car, only to have it run like a dog and I've found that one of the brand new (good quality) spark plugs I just fitted was dodgy. Just one of those things...

My point is that when you say your 88 loses compression after a few miles, are you sure that is the case? If you mean the bike seems to lose power, I am wondering whether a faulty condensor or insulation within the mag is causing the drop in performance.

I'm sure that your setting the valve clearances slightly wide will not be the cause.

Incidentally, my original Norton Owner's Handbook for the '54 88 DeLuxe gives 0.003" & 0.005" for the valve clearances. They will obviously be wider for the later camshafts and ally heads were the go then as well.

Withyour iron head, higher compression pistons will definately mean the top end will run hotter. Cast iron just doesn't radiate heat as efficiently as aluminium alloy.

I now realise I didn't respond to your asking for a stab at any spares for this model a few weeks ago.

If there is some other way of contacting you directly I would be happy to help when I can, should I have any surplus. There's nothing doing just now though.

I tend to maintain a tight grip on anything I may need for myself, but once in a while someone gets in touch with a good haul of original Dommie spares theydon't wantand I come home with a van full.

Good luck with it.

Paul

John Shorter previously wrote on Sunday January 22nd 2012 at 18.17hrs:

Hi Paul,

Thanks for your reply. I am not exactly a novice, re things mechanical (providing they are over 40 years old, modern electronics have me beat!). I have owned, and serviced many old brit & early jap bikes, built an Austin 7 special from scrap, and, until a few years ago serviced my own cars. Initially, I set the valve clearances too tight, not too wide. Regarding compression, yes, I am quite sure. When hot, there was little, or no, resistance when the engine was kicked over. I am now almost sure the valves were not fully closing. Earlier, I had suspected weak mixture, causing overheating, but, trying a 270 main jet made no difference (except to soot up the exhaust pipes!). Yesterday, I increased the tappet clearance to 0.006" inlet & 0.008" exhaust (as recommended for the 88 ss). I have not yet road tested the bike. However, after letting it run, at a fast tick-over, for over 20 mins there was no loss of compression, and it restarted on the first kick. I am not sure if my e-mail address is on my profile, but there is a good picture of the bike.

Regards, John

Hello John,

Your static run without symptoms for 20 minutes seems promising.

I'm sorry if my message gave you the impression I was labelling you as a novice. That wasn't the intention. I was simplytrying to cover all the anglesfor your motors 'going off' when up to temperature.

I have just clicked on your name and don't see any email address on the page which opens.

Mine won't be visible (I hope).

I also wrote a short message in the Feedback for Author section, but that came back with 'No email address found'.

Paul

If the valves are a little tight they will sometimes wear in if the bike is used on short trips, there is the risk of burning the seats though. The stems can also get scuffed. Its only the exhaust thats the problem usually.

Just a little pointthat Ithought would be worth a mention.

Some owners run their Iron Head Dominators with alloy pushrods inside the engines.

Nothing wrong with this as long as the tappet gaps are set a little wider than standard. Otherwise, if left at the normal 3 & 5 thou, these gapswill soon disappear rapidly followed by the engine compression.

Iron Head+ Iron Barrels + Alloy Pushrods = Problems due to expansion rate differences.

Could this be the root cause of your problems???

John Shorter previously wrote on Friday 27th January at 21.22hrs:

Thanks Phil. I think you have explained away my problem. My engine indeed has alloy pushrods, I assumed these were standard. After a head overhaul, I set the clearances to 88 ss spec. (6 thou inlet, 8 exhaust). This seems to have been a cure. The bike ran well, with no loss of compression (until the cheap head gasket blew!). I have ordered a copper one, but living in Spain, it will probably take a couple of weeks to arrive.

Nice going Phil. Good thinking!

With the lively performance of your 88 John, what do you reckon the odds are of there being an SS cam in there as well?

Even a Daytona profile would be enough to get it up on its toes, compared with a Model 7 cam.

Paul

Previously wrote:

Thanks Phil. I think you have explained away my problem. My engine indeed has alloy pushrods, I assumed these were standard. After a head overhaul, I set the clearances to 88 ss spec. (6 thou inlet, 8 exhaust). This seems to have been a cure. The bike ran well, with no loss of compression (until the cheap head gasket blew!). I have ordered a copper one, but living in Spain, it will probably take a couple of weeks to arrive.

Hello John The Orginal push rods for 1954 dominator 88 were all steel Not Alloy if You have fitted a SS cam with radiused cam followers this will tighten up the valve train as well , As Flat cam followers were used for The Manxman Cams :ie (SS)

what?????????? I think Phil already answered that? Iron heads has steel pushrods, alum heads had aluminum pushrods. As John said, he has alloy pushrods installed in his engine with an iron head, he changed the valve clearances & problem solved. He said hedidn'tknow what cam he had in his engine, and hedoesn'twant to tear down his engine to find out. Cam followers (flat vs. radius ) were not the question. C'mon class, lets follow along!

Thanks to Phil for the pushrod info! I just bought a new set of aluminum pushrods for my model 7, you probably just saved me a lot of hair pulling!!!!!!! I did notrealizethe clearance issue, thanks again!!!

Skip