Author Topic: Big Head Scrambler.  (Read 345 times)

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Bullet Whisperer

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on: January 22, 2021, 07:32:15 pm
Here is a 500 Big Head Scrambler, just after a top end rebuild, following a dropped valve.
B.W.

https://youtu.be/je6ILEk_5ig


AzCal Retred

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Reply #1 on: January 22, 2021, 08:14:01 pm
Thanks for that. Are the rockers designed differently on the Big Head? I thought that there was actually 30 PSI or so on a cold start. That plastic line looks "crude but effective" for determining oil flow - will it work on pre-unit Bullets also?
A brace of 1999 Bullets: 1 Red Deluxe, 1 Green Standard. Also, 1 wee orphan 1956 Fire Arrow project.


Adrian II

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Reply #2 on: January 22, 2021, 08:36:36 pm
This is a not very good pair of big head rockers, the rocker spindle fits in the head casting and not in separate rocker blocks like the other Reddich or Chennai iron barrel Bullets. The AVL/Electra-X rockers are similar at least in principle to the big head rockers, the UCE/EFI engine went back to separate rocker blocks like the iron barrel motors.







On my own big head engine, I got Bullet Whisperer to fit a set of USA-made rockers running on needle roller bearings from Enfield Racing.



A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


Bullet Whisperer

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Reply #3 on: January 22, 2021, 10:18:49 pm
Thanks for that. Are the rockers designed differently on the Big Head? I thought that there was actually 30 PSI or so on a cold start. That plastic line looks "crude but effective" for determining oil flow - will it work on pre-unit Bullets also?
The cold oil pressures on British Bullets are controlled by relief valves - one in the crank for the feed side, and one in the top front of the crankcase, for the return, so any pressures due to the cold cannot exceed pre set levels. That clear line has been there for a long time, by the looks of it, but the return relief valve will help protect it.
 B.W.


AzCal Retred

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Reply #4 on: January 22, 2021, 10:58:10 pm
Thanks for the info. My 1999 Indian Bullet is relief-valve free, so if it becomes a problem H's always has these:
PART No. 93140 ; £54.50 ; ROCKER RELIEF ASSY (Kickstart models before June 2002 with imperial threads)

I assume Adrian's needle rockers can't maintain a backpressure, so a non-issue.

Adrian - did you need to balance flow between the rockers? - ACR -
A brace of 1999 Bullets: 1 Red Deluxe, 1 Green Standard. Also, 1 wee orphan 1956 Fire Arrow project.


Adrian II

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Reply #5 on: January 23, 2021, 01:05:55 am
Bullet Whisperer actually built my engine, it's based on a Indian Bullet bottom end (E/S crankcases!), but with a steel con-rod and needle roller big-end. I don't think there is a pressure relief valve in the crankshaft on this one(?), but the needle roller big-end bearing should let oil escape from the holes in the crank pin more freely. Same thing on the rocker side, there's no pressure release valve at the base of the rocker feed line, but again, the needle roller bearings should offer less resistance to the oil flow, and B.W. has drilled extra pressure relief holes in the rockers and slotted the thrust washers to free up the oil flow even further.




Photo: B.W.

These and some other useful bits here (note: Hitchcocks' has these rockers for UK customers too now):

http://enfieldracing.com/page/28582-Enfield

Ref the rocker oil feed line on the scrambler, I had a BSA B40 which also had an external rocker feed line, I replaced part of the 3/16" copper tube with a length of translucent nylon hose of the correct bore so that I could also do a visual check on the rocker feed oil supply, that never caused any problems.

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


AzCal Retred

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Reply #6 on: January 23, 2021, 09:34:05 am
Thanks for the Enfield Racing link. Your BSA B40 experience is encouraging. I'm probably pretty safe trying plastic oil hose as I don't really ride when it's below 55 degrees, so I probably won't get high scavenge oil pressures from cold, thick oil.
It took a while to figure out that Brits drinking warm "room temperature" beer was probably more like 45 F, not 80F. Their perspective on cold is different! My 15W50 should do fine with a plastic insert to verify flow.
I like that 5-speed & front disc on your "Big Head". Should make it a whole new animal on the road. Don't you miss spoke tuning, though?   ;D
A brace of 1999 Bullets: 1 Red Deluxe, 1 Green Standard. Also, 1 wee orphan 1956 Fire Arrow project.


Adrian II

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Reply #7 on: January 23, 2021, 04:18:50 pm
Nope, I would put spoke tension checking under general maintenance. It's POSSIBLE that I might one day go for Morad flanged alloy rims and stainless steel wire spokes, but right now I like the look of the alloys.

Tuning is something best done to the engine, someone has just sent me an Electra-X cylinder head for me to fit the iron barrel decomp valve, and I'm trying very hard to resist the urge to send it back looking like this, though without the Tufnol dust.



Just so that you can compare Electra-X and Big Head rockers, here's an Electra-X set up on ebay Oz at the moment, note the rocker arm geometry.





Original photos here:

https://www.ebay.co.uk/itm/Royal-Enfield-Rockers-Electra-Leanburn-500313-500314-500166/383292171210?hash=item593dfe63ca:g:alQAAOSwB8Nd4M1I

On the subject of warm versus cold beverages, you would normally serve sparkling wine chilled and a good red wine at room temperature, but what do you do when some Aussie joker comes up with a sparkling RED wine? Serve it lightly chilled?

https://www.averys.com/product/Red-PRD+Sparkling+Wine/McPherson%27s+The+Full+Fifteen+Sparkling+Red-NV/35935NV

Traditional British ales, stouts and porters are supposed to be served cellar-cool, not chilled, I agree actually serving them warm IS wrong, but the fad for (e.g.) extra-chilled Guinness is something I don't get, how are you supposed to taste anything?

A.

Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


Karl Fenn

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Reply #8 on: February 27, 2021, 09:01:58 pm
I think needle roller would be a step up to the shaft BMW used needles on the air heads they never gave any trouble l remember these from the 70s cheap but wore out quick, needles are a long term fix for the rockers.


Adrian II

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Reply #9 on: February 27, 2021, 09:50:26 pm
The Electra-X/AVL rockers run directly on their shafts, no bronze bush or needle rollers on these. Steel on steel with an oil slot for pressure relief seems to work OK for these.

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


Bullet Whisperer

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Reply #10 on: February 28, 2021, 03:15:46 pm
The rockers I made for the Big Head on our 350 racer, from butchered rockers from old RE twins withstand 9,500 RPM, running steel to steel.