IRON 4G PISTON/BORE CLEARANCES

Singles, twins and fours.
malcolm.johnson
Posts: 95
Joined: Fri Aug 19, 2011 12:09 pm
Location: Knaresborough, North Yorkshire
Contact:

IRON 4G PISTON/BORE CLEARANCES

Postby malcolm.johnson » Sun Nov 18, 2012 9:27 pm

Following my post back in july re pistons for my iron 4g, that had been bored and little ends re bushed, to take + 040 BMC pistons and then left to rust, I located a set of nos + 060 BMC pistons after months of searching. Got them from Bruce Longman (why did I not try him sooner) together with other parts and a very useful article on building the cylinder head and rocker box - thanks Bruce.

Q1. Do members have any recommendations as to piston / bore clearances to give Mr. Reborer?

Q2. This may seem daft, but is there a front and rear to the cylinder head? Mine came totally stripped to the bare casting and I seem to be able to fit it either way.

Just a note about using BMC pistons.... AE 16179 ( MG Midget I believe) do not need any machining at all save re-bushing connecting rods, whereas some BMC pistons need the crown machining to correct piston height.

malcolm.johnson
Posts: 95
Joined: Fri Aug 19, 2011 12:09 pm
Location: Knaresborough, North Yorkshire
Contact:

Postby malcolm.johnson » Mon Nov 19, 2012 1:22 pm

I forgot this one and is also about the orientation of components. The connecting rods on my iron 4g are the later with the shell bearings. Are there any thoughts which way round they should be fitted to the crank in relation to the shell indents on rod and cap, which are on the same side of each assembled rod. Does it matter? I am aware that pistons have differing orientation to front and rear crankshafts, due to different thrust faces, does it affect the rods too?

nevhunter
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 3933
Joined: Tue May 10, 2011 9:42 am
Location: Victoria.. Australia.
Contact:

Postby nevhunter » Mon Nov 19, 2012 10:09 pm

The recesses in the rod , if they are orientated to face each other , ( both on the same side when correctly assembled) can be fitted any way around. Make sure all caps match . For piston clearance with BMC pistons at a guess I would use .002" more clearance than for the car. depending on the material (metal alloy used) the design, (Some have a "T" slot). If the piston has a 3 piece stainless oil ring I would replace it with a conventional early type iron oil ring. You may have to alter the size of the gudgeon pin bosses to obtain the correct end movement. 3 mm should suffice. total end float. Nev

alalovell
Posts: 12
Joined: Tue Jan 08, 2013 12:50 am
Contact:

Re: IRON 4G PISTON/BORE CLEARANCES

Postby alalovell » Wed Jan 09, 2013 5:30 am

Hi I am new to the club and put the BMC AE 16179 A +.040" pistons in a 4G 30 years ago then had to leave the bike until recently. I pulled the block off,all checked OK then ran it for 80Km and one of the rear pistons grabbed and is stuffed...others are all ok and the problem bore cleaned up ok. I didn't realize getting another piston to match would be an issue. Does anyone have one...even secondhand , or a new set to suit that they are happy to sell ?
I noticed in a post that Bruce Longman was able to help out Malcolm Johnston ...what is the best way to contact these guys for advice? Thanks, Alan

User avatar
john.nash
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1121
Joined: Mon Feb 14, 2011 4:46 pm
Location: Herefordshire. Mud capital of the world
Contact:

Re: IRON 4G PISTON/BORE CLEARANCES

Postby john.nash » Wed Jan 09, 2013 9:43 am

John "Josh" Nash
webmaster@arielownersmcc.co.uk
AOMCC No.4119
2009 royal Enfield,1978 t140 bonneville, '67 CJ750, 196-ish Ural M62 outfit, 1960 k750, ''51 kH500, ''49 soon to be Ariel bobber, 47 VH twinport, '44 Ariel WNG, '43 Ariel WNG, '41 Ariel WNG and piles of rusty scrap ....

malcolm.johnson
Posts: 95
Joined: Fri Aug 19, 2011 12:09 pm
Location: Knaresborough, North Yorkshire
Contact:

Postby malcolm.johnson » Sun Jan 20, 2013 8:29 pm

Thanks to this forum and Bruce Longman, I am pleased to report that my iron 4g now runs and although not yet used under load, has consumed a few pints of petrol over a number of runnings and seems to be freeing up nicely. I used the =+ 0.060 AE16179 pistons previously mentioned in front bores with 0.0025 clearance and rear bores of 0.004 clearance as advised by the engineering firm I used (also seemed to fit AOMCC views). All bores bar one cleaned up perfectly and one just left a small "rust stain" in the lower bore below the ring travel. Still have some issues with the carburettor weeping, but we are getting there. It has not run until now for around fifty years - quite a thrill. Now I may be able to help Alan, since I have a set of AE16179 + 0.040 pistons (no rings though), that did not get to be used from when the engine was originally bored (by Healey`s around 1975 I have found out) and then allowed to rust. If you wish to contact me Alan- not sure how you do that? Malcolm.

User avatar
john.nash
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 1121
Joined: Mon Feb 14, 2011 4:46 pm
Location: Herefordshire. Mud capital of the world
Contact:

Re: IRON 4G PISTON/BORE CLEARANCES

Postby john.nash » Sun Jan 20, 2013 10:11 pm

malcolm.johnson wrote: If you wish to contact me Alan- not sure how you do that? Malcolm.


The forum has it's own messaging system.

You can send him a "personal message" (PM)
Under Alan' name, on one of his posts, is the little "PM" link

Provided you are logged in, then click on that and send him a note .... he'll get an email notiication that you've done so
John "Josh" Nash
webmaster@arielownersmcc.co.uk
AOMCC No.4119
2009 royal Enfield,1978 t140 bonneville, '67 CJ750, 196-ish Ural M62 outfit, 1960 k750, ''51 kH500, ''49 soon to be Ariel bobber, 47 VH twinport, '44 Ariel WNG, '43 Ariel WNG, '41 Ariel WNG and piles of rusty scrap ....

alalovell
Posts: 12
Joined: Tue Jan 08, 2013 12:50 am
Contact:

Re: IRON 4G PISTON/BORE CLEARANCES

Postby alalovell » Mon Jan 21, 2013 2:13 am

Thank you John and Malcolm, What a wonderful feeling to have a bike like that for quite a while then hear it running finally. From the care you have taken you won't experience my sort of stuff up. I have written to Bruce Longmann and am due to phone him today ...I sent a message to you Malcolm, via the site, but couldn't have done it correctly so I will follow John's instructions.
Cheers, Alan


Return to “Four stroke”

Who is online

Users browsing this forum: No registered users and 5 guests