A10 cylinder head reconditioning

[a101960]

Some of you might be interested by this

I have just received my head back from the Cylinder Head Shop after having had it overhauled. It has been fitted with new valves, unleaded valve seats, and has been gas flowed. Here is a summary of the refitting instructions and what might be needed to get the best from the newly overhauled head.

?Having your seats cut or recut so accurately on the Serdi 100 will cause an enrichment of carburation on all engines. This is because your valve is now sealing more efficiently, and where we have fitted new guides or guide liners less air is being drawn down the side of the valves than before.. Your head will need to be re-carburated . For example fit next size down needle jet (106 down to 105). Machine or buy weaker slide (No 3 fit  3 1/2).

Main area of fuel change is the slide, then needle and jet. Generally all need weaker setting. Main jet may need richer jet - do the throttle checks first, but immediately. It may be that your ignition timing will need to be retarded by 2 degrees or more depending on how more efficient we have made your head. The head is claimed to be far more efficient than ever it was when new. Which is why these adjustments might be needed.

Always retorque  head and reset tappets after 10 miles or so and again after 500 and 1000 miles.

If possible use NGK iridium plugs.?

It will be interesting to see how all this turns out in practice.

Does anyone know if there is a suitable non resistive plug iridium available?

[groily]

Extremely interested and thanks for sharing. Don't know about the plugs Q, but on the main points they make, I am amazed and impressed. That is some difference, between say an 'ordinary' head overhaul, valves, guides, etc, and one of theirs. Sounds as if you're in for  lot of fun, and better performance all round. You deserve it, because I suspect this was not a cheap option. As for making 2 degree changes to ignition timing, good luck on that too - without taking off the primary case or the timing cover and rigging up a degree disc, and without a very sensitive meter to measure the resistance across the points in the mag to get the point of 'break' with ultra precision (or figuring out how to get a strobe on the thing) that could be a challenge. Be fascinated to hear how you get on, as I'm sure a lot of folks will be. Think I'm envious!
I do agree with the retorquing though, per previous threads here, although it may be a bit over the top! It's just a peace of mind thing with me.

[fido]

I hope they have not reduced the BSA specified running clearance of the valves in the guides. They need to be quite sloppy or you can get seized valves.

[Brian]

I have to say I would be take their advice with a degree of caution. If it was me I would leave all the jetting etc as it was. Their work may be good but I cant see it making that much difference. Even if they are correct it will only run slightly rich which wont hurt. And as Fido pointed out the valve guides need the correct clearance. We are dealing with older engines not modern ones which can run smaller clearances. Just my thoughts........ Brian.

[a101960]

This evening I fitted the head, and tomorrow I hope to finish the job off. Can anyone clear up a point that I am unsure about? Before I fit the rocker cover is it necessary to loosen off the tappet adjusting screws? I can find no reference to to this matter in Haynes or my copy of BSA service sheets. I know that this may seem a daft question to ask, but this the first time that I have ever done any work on an A10 top end. If I get it all together I will report back and let you know how the engine feels after the head work, and what the colortune indicates as far as the mixture is concerned.

[groily]

I always do because it makes it less difficult and less stressful to tighten down the rocker box against whatever valves are open. But not sure if it's really necessary. Hard bit is getting the darn invisible pushrods to seat reliably in their cups, even with the comb - see previous threads here (somewhere!) where someone gave really good advice on this when I was struggling and whining. You're going to have to adjust the valve clearances anyway, so there's nothing to lose by taking the tension off. . .

[RichardL]

As for mine, the first time I did it, I did not back off the adjusting screws on the rockers. It seems to me that no matter how far you back them off you will still be compressing valve springs when you tighten down the rocker-box nuts. Nevertheless, I suppose it might make it a bit easier to get it seated. The one thing that I would watch for (and I will when I put my head back on) is that it may make locating the pushrods in the cups less positive and secure.

Someone here that I trust more than me is going to chime in and give us a clearer answer.

Richard

[groily]

Richard's right there'll always be some spring pressure to overcome, I just like to get it down to the minimum so the rocker box goes down as easily and evenly as possible. Pushrod assembly is no more awkward with the screws backed off than it is anyway - which is bad enough! I am not a fan of rocker shafts integral with the lids, as I think it is better to have the spindles located in lugs cast integrally with the head. That way it's easier to assemble, easier to adjust and the clearances are more likely to stay where they are set for a lot longer (especially where the head's iron and the rocker box alloy). But hey, it doesn't really matter . . . they work well enough for 'cooking' engines where valve clearances are relatively enormous. Every engine has something that's a pain to assemble or adjust, but I reckon the A 7/10 deserves a special award for the top end (wonder why it wasn't continued into the unit series!). Whining again.

[LJ.]

Most definitely slacken off the tappets before tightening down the rocker cover. Reason for this is that it lessens the stress on those corner bolts that can so easily be stripped. I even go as far as removing the tappet screws altogether so that there is  no pressure what so ever. Nothing worse than the rocker seating down unevenly and there is a heck of a tension in them valve springs, one or two bolts compressing them is asking a bit much.

Dont worry too much about gaskets and sealing the joint between head and rocker yet as you'll need to re tighten down the head again after a few miles, I'm sure you can put up with a little leakage untill then... then do the sealing job properly. I know its a pain having to remove the rocker cover again but it is very much worth while... I did find that my head bolts needed just that slight turn and the middle head bolt is probably the most important one being between the cylinders.

[a101960]

Laurence that is an inspirational idea. I am off to do battle.

[a101960]

The cylinder head is now fitted and the engine runs! The initial start up was interesting to say the least. The engine fired up second kick, but would not pick up. It ran just fine on one cylinder but there was a lot of spitting back from the other one. There was no response to the throttle any attempt to increase engine speed caused the engine to fluff and die. Eventually things settled down and the other cylinder started working properly after I put the Colortune into place to have a look at what was going on. I adjusted the pilot screw until I got the required Bunsen blue burn. There is still a very occasional spit if I snap the throttle open from idle, on the road there is no evidence of spitting, and when I took it out for run this evening the engine pulled like a train and picked up with out any protest. I suppose that there could be a sticking valve, anyway I will run it around for a while and see how things progress. The other thought that has occurred to me is that the carb might have a partial blockage due to standing for a while. In my experience even if you shut the petrol taps and run the engine until the fuel runs out, this does not in itself guarantee that  the nasty yellow gum will not form. By the way the petrol had been in the tank all winter so it could also have been stale fuel. That said I work for the Air Force, and it is standard practice to store aircraft with full tanks to minimise water contamination due to condensation. The fitting of the rocker cover is a truly awful job, less so if you have someone to hold the comb steady. I managed to do it in about 4 minutes with assistance, but I had wasted nearly two hours trying to do it on my own. Could the spitting back be caused by over advanced timing, or from what I have described does anyone think that it is due to a weak mixture? The carb is set up exactly as per spec: Amal type 389  slide 3 main jet 420 and 25 pilot. The needle jet is set on the second from top notch which is exactly where it should be. I am eager to get a few miles in but that wont happen in the next few days because the weather forecast is for rain, rain, and yet more rain. Incidentally. The reason for pulling the head originally was because the top end rattled no matter how much care I applied in setting the  tappets, and I was burning oil once it had warmed up. It transpired that the right hand inlet guide was loose. Anyway the top end is now a lot quieter, and there is no smoke.

[KeithJ]

Just picked this up on a Google search and wondered how the head worked?

[a101960]

Just picked this up on a Google search and wondered how the head worked?

It has worked fine ever since. Time and money well spent.
John

[kiwipom]

hi guys, just doing the same job. Heated the head to knock the old guides out (they were steel ones) did as Musky said and heated head to 200+deg in oven (new guides were in freezer all night) still had to hammer the new guides in, hope I never have to get them out, now have to take to head shop for guide reaming,cheers 

[muskrat]

I hope that was 200 C and not F. I've only ever had to give them a light tap if they don't go home by themselves.
Take the valves too as the seats will more than likely need to be cut.
Cheers