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Arrow Torque Setting

Posted: Tue Apr 01, 2014 10:27 am
by Ivor Collins
Hi to all
I am a new member today (April Fools Day)! and I am looking for some help with technical info.

I am rebuilding the Arrow I bought and used as my only form of transport back in 1970. It has been in storage for the last 40 years following a sheared cylinder stud which I managed to prise out a few years ago with the help of a spark eroder. I have acquired 2 more arrows over the years, one of which appears to be a golden arrow so this one will be the first rebuild of a tri-cycle!
I have looked up torque settings for 5/16 UNF fixings but this application where the stud is screwed into aluminium and the 'nut' being much longer than a standard nut must require a different setting. The original workshop manual does not contain any torque settings, I wonder if the factory even used torque wrenches in the assembly processes? I know that when I progressed to an aluminium engined Sunbeam Stiletto car (sorry) a few years later and foolishly allowed Bristol Street Motors replace the head gasket on it, they cracked the head for me either by failing to use a torque wrench or, more likely, pulling down one bolt to full torque without any progressive sequence across the head.

Anyway, info on torque setting or thoughts on how risky it would be to use of some 12:1 compression ration heads I have from Carter Engineering (anyone remember them) would be gratefully received.

Thanks Leira

Re: Arrow Torque Setting

Posted: Tue Apr 01, 2014 3:06 pm
by bh.sprint
I'll post a reply tomorrow, when I've found the details for the cylinder head torque values.

I assume this is genuine !


Re: Arrow Torque Setting

Posted: Tue Apr 01, 2014 9:16 pm
by Ivor Collins
Thanks BH and yes, its a genuine inquiry despite it being April Fools Day. I would be interested in knowing the source of the torque data and if extends to some of the other important fixings on the bike. I think the manual does specify a torque for the crankshaft centre bolt but its the only one I've seen so far.
Do you know anyone on 12:1 heads???

Tomorrow is a foray of collecting wheel bearings, some gentle sand blasting of the heads to remove 50 years of aluminium oxide and straightening some very bent riders foot pegs.

Thanks for the reply.

Posted: Wed Apr 02, 2014 11:42 am
by Roger James
Brian, Ivor,
I dont think the factory issued any torque data relating to the head bolts on the Leader/Arrow engine but I know that club member Roger Lee has mentioned a torque figure he uses in a message on the Leader/Arrow forum but I dont remember what that figure is, will do a search and see if I can find the message, goes back a long time though, perhaps a couple of years. Jess

Posted: Wed Apr 02, 2014 12:40 pm
by brenton.roy
There is a factory document in the club library which gives two stroke head bolt torque. ... spx?id=245

Re: Arrow Torque Setting

Posted: Wed Apr 02, 2014 2:07 pm
by bh.sprint

For the heads the people who rebuild engines work to 18 ft lbs, initially working to just under the 18 ft lbs figure and then after running the engine torque to the 18 figure.

Re the heads . I've only heard of the racing people using them, some riders say they narrow the power band , others feel they do not give much usable increase in power. Ron Phillips of Fahron Engineering is possibly the best person to ask. He's in Lindby Notts. 0115 9634123.
He makes the alloy cylinders, a mine of information but he's usually very busy.


Posted: Thu Apr 03, 2014 1:09 am
by nevhunter
Higher compression on a 4 stroke makes it suck in more air. This doesn't happen on a 2 stroke which uses crankcase displacement and pressure waves( if you are lucky or clever). There are 2 ways of measuring CR on a 2 stroke. One uses swept volume above the exhaust port. Over compressing a two stroke can cause detonation and piston/ring damage. Some of the designs incorporate a "squish" band which seems to work. Nev

Re: Arrow Torque Setting

Posted: Fri Apr 04, 2014 9:17 am
by Ivor Collins
Thanks for all the replies on high compression heads and torque setting, it will be good to finish the engine build using this info.

Although the 12:1 heads seemed like a good idea when I was a teenager, it may not have been one of my better moves and, as they were brand new heads, I will see if I can machine the 'top hats' to return them to normal but maybe I should firstly be looking into current ideas on the best shape for squish and swirl??

I have plugged and plated the crankshafts to hopefully increase the efficiency of pumping and I guess this increases the compression pressure anyway by more efficient filling of the cylinder.
I am aware of the different methods of measuring compression ratio on a two stroke cylinder and have always believed the factory figure of 10:1 is the full swept volume but whichever it is I assume someone at Carter Engineering calculated the machining needed (though this may just be my optimistic view) to produce the 12:1 heads. It would not be too difficult to work this out and I wonder if anyone has already measured the volume in the head and the dome of the piston crown?

I am aware of the expertise available at Fahron Engineering, though only from the Classic Racer magazine article of July 2005 but my (non) budget for the job necessitates doing the majority of the work myself and only taking on mods within the scope of the mig welder, Bridgeport and Colchester I have access to.

I will be moving on to preparing the frame and panels next so need to consider the the effects of our wonderful ethanol enhanced petrol on the
fuel tank. Do I need to treat the tank or will it successfully resist this evil fluid?


Posted: Fri Apr 04, 2014 9:33 am
by Ivor Collins
brenton.roy wrote:There is a factory document in the club library which gives two stroke head bolt torque. ... spx?id=245

Thanks for this link for torque settings but I am unable gain access.
Do I need a different log on or am I just techno challenged?

Posted: Fri Apr 04, 2014 11:45 pm
by brenton.roy
Hi Ivor,
No you aren't challenged! This forum is attached to the AOMCC member's library, which has it's own passwords.
Regards, Brenton