Britbike forum

Classic British SparesKlempf British PartsBaxter CycleThe Bonneville ShopLowbrow CustomsGirling Classic MotorcycleLucas Classic MotorcycleHepolite PistonsIndustrial tec supplyJob Cycle

Upgrade your membership to Premium Membership or Gold Membership or Benefactor or Vendor Membership

New Sponsor post
Sales and Closeouts
by BritCycleSupply - 03/24/23 4:38 pm
New FAQ post
Disappearing User
by Boomer - 03/09/23 9:27 pm
News & Announcements
Premium members! 🌟
by Morgan aka admin - 03/27/23 7:40 pm
Gold members! ⭐️ ⭐️ ⭐️
by Morgan aka admin - 03/18/23 4:57 pm
How to guides - Technical articles
How to Straighten Your Amal Carburettor Float Bowl
by Stuart Kirk - 03/18/23 8:38 pm
Sixth edition is now out:
The Gold Star Buyer's Companion
Comment Guidelines: Do post respectful and insightful comments. Don't flame, hate, spam.
Member Spotlight
Mountain that speaks
Mountain that speaks
Scottsville, NY
Posts: 27
Joined: February 2022
Top Posters(30 Days)
DavidP 92
Lannis 81
Top Likes Received (30 Days)
kevin 34
DavidP 26
Newest Members
NeilD, Olknuckles, Darío Tzvir, BSA1nut, Steve G.
12,445 Registered Users
Forum Statistics
Most Online230
Mar 11th, 2023
Random Gallery photo
Photo posting tutorial

Previous Thread
Next Thread
Print Thread
Joined: Aug 2001
Posts: 129
Britbike forum member
OP Offline
Britbike forum member
Joined: Aug 2001
Posts: 129
Hello Everyone, i am pretty puzzled by the cylinder head bolt lengths of pre unit 650 triumphs with alloy head. i ordered head bolts as listed in a 1961 650 parts book. the head bolts i ordered were 4 outer domed head bolts 70-2873 they have a under head length of 3 inch 3/4 long. also 2 cylinder head inner bolts with threaded extension for head steadies 70-1596A under head length 5 inch 7/8 long and two inner head bolts with no extension also under head length 5 inch 7/8 long. when the parts arrived the long inner head bolts has written on the label cyl-head bolt p/unit TR5 T100. i think this is a parts book mistake. it lists the iron cyl head with outer domed head bolts as 70-0327 which is the same as unit 650 triumphs. also the long inner bolts for the iron head are 2 cylinder head inner bolts with threaded extension for head steadies as 70-1596 which is the same as unit 650 triumph. and two inner head bolts as 70-1484 with no extension, the book quotes 5 inch 3/8 under head length but they are 5 inch 5/8 long which is probably another parts book mistake. which ones are correct for the 650 pre unit with a single carb alloy head fitted. does anyone have a bike apart where they can measure the under head lengths of the bolts and please let me know. this is battering my head. just as a note, i have a 500 close pitch fin alloy cyl head plus a alloy 650 single carb 8 stud cyl head and a unit 650 9 stud cyl head to compare with and the depth of outer head bolt hole is the same on all 3 cyl heads. i am pretty good on triumph knowledge but today might be a learning day and i am always finding something new even though i am approaching 60 years old. as stated above, any info gratefully received. cheers. billy.

Last edited by billy banger; 02/03/17 4:48 am.
Triumphs on eBay
Joined: Jul 2015
Posts: 50
Likes: 5
Britbike forum member
Britbike forum member
Joined: Jul 2015
Posts: 50
Likes: 5
Part # 70-1956 and 70-1956A are different lengths. 70-1956 has an under head length of 5.625" (5 5/8") and 70-1956A is 5.875" (5 7/8"). The 1956A is used for alloy 500 pre unit heads only. The head washers are .095" thick so keep this in mind when mocking it up.
Here are the under head lengths for the .375" head bolts I have in my notes:
70-1956 5.625" (w/standoff)
70-1956A 5.875" (w/standoff)
70-0327 3.400"
70-1484 5.625"
70-2873 5.750"
Hope this helps out with figuring out what you need- Dan

Moderated by  John Healy 

Link Copied to Clipboard
British Cycle SupplyMorries PlaceKlempf British PartsBSA Unit SinglesPodtronicVintage MagazineBritBike SponsorBritish Tools & FastenersBritBike Sponsor

© 1996-2023
Powered by UBB.threads™ PHP Forum Software 7.7.5