Hi to anyone who can help me I've just got my first bike ever apart from 125s etc when i was a lad but now I've gone and bought a Bonneville T140v 1977 its a bit of a wreck but i suppose that's half the fun. I'm an absolute novice when it comes to bikes so any help will be much appreciated. So with your help hopefully one day i will be able to dish out a bit of advice of my own. Hope i don't start boring you lot I've got a million questions, Here's my first of many problems- I didn't realise when i bought it but the cylinder head is off a Tiger tr7 i'm pretty sure anyway, the bottom end is stamped T140V NP78234 so is the frame so I'm petty sure it was originally a Bonnie, My question is can i get a T140 Cylinder head and do a straight swap for the tiger cylinder head what else is different that i will need to change. I'm assuming that the Barrels on both bikes are the same. Ive seen cylinder heads advatised etc on ebay and here and there but they don't have the rocker boxes on just bare so if i got one of these can i transfer all my other parts from my cylinder head to the new T140 head thanks in advance for anyone's help
Hello and welcome, Jim. I can't recall off-hand the exact details but I THINK you'll find that the Tiger TR7 is, in essence, a single carb. Bonneville, so the head has probably been put on the T140 to provide a relatively simple solution to the eternal problems of twin carbs. - balancing, tuning and fuel consumption. Essentially, unless you're striving for total originality, the bike will operate well (perhaps better!) on the TR7 head as long as the sinlge carb. is jetted to suit - especially if the specs. of both bikes reveal differences such as valve sizes/angles, etc. Why not build the bike up and run it as is and, if you do seek the originality, just keep a vigilant eye on the usual places for a used T140 head whilst you enjoy the pleasure of riding the machine? My 2 penn'orth. Good luck with it - we'll look forward to the build operation reports!
Many of the unit heads are interchangeable if you know the way around them, if you have the correct year single carb head on your bike with the correct year rocker boxes then its an easy job to swap the head for a twin carb head.
Jim Hargreaves Welcome to the family. Don't see why you would want to swap as it should be a single carb head and easier to work on as the bonnie will have the twin carb. As to swapping you really go by studs there are i believe eight stud heads and 10 studs. Then you will have to set up the carbs and cables. If you have a single airbox you will have to find the twin airbox and make sure it fits or you need to run K & N Filters. Hope this helps. Do your build in the restoration and projects section and let the inmates take the journey with you. Don't forget lots of pictures. Joe
Agreed most of the heads and rocker boxes are interchangeable with a few exceptions where the fun starts is there are several different lengths of push-rod and tubes but you should be OK with a straight swap for other unit stuff.
thanks for the advice i was after some originality but maybe i might just go for getting it running i'm a bit wet behind the ears yet to start swapping heads.