[Adrian II]

Another small task is done.

The carb-to-head flange adaptor is sorted, but there’s still a bit of an issue with the carb. Fans of the Dell’Orto will know that some of their carbs come with stubs that fit into a short connecting hose, while some of them clamp onto a stub fitted to the cylinder head. The carb is off a BMW R90S, BMW specified the clamp-on type (as did some big Ducatis), with a nylon sleeve between the carb and the stub (which was steel in the BMW’s case).



The O/D of the nylon sleeve is 48mm, the I/D of the nylon sleeve (therefore the O/D of the BMW stub) is 45mm. Only problem is my Mikuni mount’s stub is 44mm, the carb clamp won’t take up that much slack.



While I was tempted to get my son-in-law to knock one out in plastic with the smaller I/D on his 3D printer (which I might still do if the following doesn’t work), a search on ebay revealed that there was some alloy tubing exactly the right size to marry up the two, viz 48mm O/D x 44mm I/D. A short length of it arrived today, so I sawed off a piece to fit into the carb.  The is bore is slightly too tight just to push onto the Mikuni stub, but heating it up a little let me tap it on with a mallet, I also had a good smear of blue Loctite between the two. Could have used stud and bearing fit grade, but I might want to remove it at same stage, e.g. if I ever want to fit a Mikuni.



I will also need a short length of alloy filler tube, with a little notch to clear a fuel drilling, but that’s on order too.



Time to offer the carb up, now doesn’t THAT look sexier than a Mikarb CV29? I might still go for an air filter, I have not finally decided yet.



Loads of room for the magneto too, again if I need to revert to a Lucas SR1, it looks like there’s still plenty of room. Good. I am alsofairly condifent that the PHM to under tank clearance issue I ran into with Not A Fury should not happen here. The crankshaft bearings are due next week, while the Hitchcocks’ crank waits patiently in its carboard box just behind.



Getting closer.

A.

[ace.cafe]

Very sexy!

[Nitrowing]

Looking good 

[Adrian II]

Adding weight, though! 

A.

[Nitrowing]

Adding weight, though! 

A.

I'll wager it's lighter than the standard airbox & filter 

[AzCal Retred]

Beautiful work, as is usual for you! That screen keeps out gravel, loose coins, errant fasteners, etc. Skip the air filter, you're not riding in Arizona!    - ACR -

[heloego]

Nice, Adrian!
That alloy sleeve was a good find, too! Looks great! 

[Adrian II]

Just a quick few minutes spent on the head this afternoon, the decomp valve arrived, so I finished off counter-boring the decomp valve hole.

Also trimmed and smoothed the rough/sharp edges where the threaded hole meets the combustion chamber.





Thought I'd better check for carb clearance with the other Electra-X based engine that's still occupying the project frame, looks like I was right about there being enough carb to underside of tank clearance. However, clearance between the bottom of the frame lug for the head steady and part of the Dell'Orto's accelerator pump looks like it will be minimal, the underside of the lug may get 2mm trimmed off it on the right-hand side. I will have another look once the engine is built and fitted.

A.

[AzCal Retred]

Adrian - do you polish the casting roughness out those combustion chambers later or have them ceramic coated? I've heard of using ceramic inside the exhaust port also for additional head heat rejection. Or maybe you've found that there's no operational difference?  - ACR -

[Adrian II]

I have never tried to polish the inside of the combustion chamber on these, they're not that bad, though the iron barrel Bullet's combustion chambers were always machined, which makes them look a little rougher by comparison. As far as I know only Ace has used ceramic coating on the inside of these heads, but AFTER the combustion chamber has been built up with weld and re-worked. I have however smoothed off the edges of the combustion chamber as well as the decompressor hole.

There are some areas where these heads can use a bit of work.

1. Inlet port. I posted a picture of the stock port recently, what's with the oval-ish port shape, 32 x 36mm, roughly? The stock carb on these was only a CV29. Dell'Orto make a carb with an oval port, maybe I should have bought one of those for it. Anyhow, it makes opening up for a larger carb easy.

2. Exhuast port. These are terrible on a stock head, a very small hole, and rough barely describes the finish. With the narrow inner bore lean-burn exhaust pipe it probably wasn't worth the factory's time to finish them properly, that was left to us!

3. Valve seats. For some reason the outside edges stick out into the combustion chamber by about 1mm, on this head I had them cut back some years ago so that the outer edges are flush with the combustion chamber surface. Also they're not smoothly blended into their respective ports, with the inlet valve seat in particular actually sticks out into the inlet tract slightly.

I gather that the Ace Fireball conversion for the AVL head deals with all of those issues.

That said, Bullet Whisperer managed to get a tuned Electra-X to do 103 mph with a totally stock head, this was left unchanged at the customer's request. So as imperfect as they are, you can still put together a decent engine with one.

Today I got the alloy tube to finish off the carb mount.



There is a teeny hole drilled in the carb as part of the idle circuit, but you can see where the end of the mounting stub could obstruct it.



Just needs a groove filed in the end of the stub.



A.

[ace.cafe]

Yeah, we did chamber and exhaust port coatings on all the Fireball heads.
The AVL wasn't really needy for it because it has plenty of cooling ability as it is.
But, there are still some advantages of the coatings, and they don't cost much.

[Adrian II]

Just a little timing cover work today.

Sooner or later you realize that the AVL timing cover won't fit. It looks as though it OUGHT to but try it...

What's the problem?

1. Cam spindles. The adjustable spindle ends on the AVL engine are reduced in diameter from ⅝" (15.88mm) to 15mm. Why? No idea. If you want to use fixed as opposed to adjustable cam spindles (that'll be me) you have to break out the ⅝" reamer or drill as the old design uses a ⅝" diameter for the entire length of the spindle. Or so I thought. Turns out Henry Price was able to get some fixed spindles for very late iron barrel Bullet with the reduced end diameter. That was a new one on me, but here one is on the right next to the usual type.



However the AVL timing cover I'm using already had the holes reamed out to ⅝", so that's one job less. So where's the other problem?

2. Idler pinion spindles. With a crank-mounted ignition the AVL design has no idler gears to drive a contact breaker, so neither the timing side crankcase nor the inside of the timing cover is fully machined.



It needs to look like the inside of the iron barrel's timing cover.



The good news is that the part-drilled top hole and the un-drilled lower hole (which still has an indentation for the drilling) picks up a 1/2" drill in pretty much exactly the right place to line up with the idler spindles in the crankcase.



That just left me needing to mill the ends of the holes in the cover to match the depth of the ones in the iron barrel timing cover. My improvised milling machine (best not to ask!) managed to do the job, not prize winning stuff but it checks out fine against the i.b. cover now.





Fits fine now.



A.

[heloego]

Nice work, and glad it went easily enough for ya! 

[ace.cafe]

A lotta work!

[Adrian II]

Actually one of the easier jobs! 

A.