Trumph 1940 Speed Twin

[Hoghead]

Nice!

[Dexter]

Following a few rides end of last year with a misfire that just got worse and an exhaust pipe that had oil in it...I thought it was time to look at a top end rebuild. I took the top end apart and removed the valves and found some play but nothing great so went the next stage and had the barrel off and removed the pistons, bores were all ok not much in the way of cross hatching present but no scores or lip at the top. So a plan was hatched and I went all in with new valves and guides + new next size HC piston and rings. Once everything had arrived I took the lot to my local machine shop and ultimately when they check a bit further the top ring on the oily side had over a 1mm gap which begs the question who had been playing some time in the past... I hope to pick this lot up soon and start the rebuild here's a couple of pictures of the guilty parts.

[Hoghead]

Wow -that gaps like three times what it should be?
Bet that's gonna feel good when it's back together. Did you do a compression test before you tore it down?
Those twins feel sweet when they are right.

[Dexter]

Wow -that gaps like three times what it should be?
Bet that's gonna feel good when it's back together. Did you do a compression test before you tore it down?
Those twins feel sweet when they are right.

I didn't have a compression tester handy so I bit the bullet, the Mag had been rebuilt last year so there was not much left to point the finger at, the best bit was it flew with even those issues so it could be a nice surprise when its done....

[Hoghead]

Should start easier too.Not they were ever difficult unless badly set up.

[Dexter]

How I fixed my droopy handlebars.....
So the 1940 Speedtwin has suffered from perished isolation rubbers on the handlebar mounts, with one side worse than the other so after a ride the bars were out of level.
First part find replacement isolation rubbers - bought from "The Rubber Man" from memory under £15
I have added a few pictures of what I found so I will let the pictures do the talking all I would add was to do one side at a time so the girder spring does not force everything out of position - test ride now waits of the return of the engine parts for the top end rebuild...and the sun has been out all day........

[Dexter]

Bit more progress with the engine

[Hoghead]

Haven't seen a Triumphs innards for a long time. Great motors. You still using RR56 conrods?

[Dexter]

Haven't seen a Triumphs innards for a long time. Great motors. You still using RR56 conrods?

Not sure on the conrods didn't need to do anything with the bottom end no play so left alone, engine is now built and the lock wire is getting some action also splashed out on a new tell tale , final checks then tank and see if it fires up.

[Hoghead]

Looking good!

[DoomBuggy]

I love Brit bikes, they can be so mechanically elegant, form following function.

[Dexter]

I love Brit bikes, they can be so mechanically elegant, form following function.

Thanks

So its finished bar some final final tinkering its popped and banged but not yet fired completely into life but its close, so here is how it stand as of today.....i have also changed the out the bars but will wait till after a proper ride to be convinced

[cisco]

Great work and congrats on a fine looking final product.

[Dexter]

Great work and congrats on a fine looking final product.

Thanks still a few more tweaks to go yet, still doesn't want too start so further investigation required......

[Dexter]

It lives - so after a few teething issues (read dodgy spark plug ) and like all issues it takes time to retrace and recheck everything even though your convinced it should be ok, the spark plug in question did show a spark but on closer inspection seemed to miss ever other spark, once replaced fired up almost fist kick just like before the rebuild - every days a school day...... Now its time to put some miles on it ready for its first track day.

[Hoghead]

Excellent job! Plugs....always worth a double check.

[Dexter]

Excellent job! Plugs....always worth a double check.

So working through setting the carb up its running a Amal TT9 and some of the issue wasn't helped by being to rich on the mixture screw , i also talked to "The Green Spark Plug Co" who highlighted that that carb set up could be leaving a deposit on the plugs which would cause the lack of spark, this was sort of proven when following a 40 mile ride the following day no pops or bangs - fitted new plugs fired up first time, so still some more tuning work to do will be taking the main jet down a size to see if this make any improvement but this will be done at the track.

[datadavid]

Sweet bike, im gonna get an overbore done to mine too soon. Ring gaps about as wide as yours but it doesnt smoke..just getting sloppy, bottom end needs done too..
Anyway, about the stock rr56 hiduminium alloy rods. The thing is they are very durable but the alloy weakens with age and heat cycling. May last forever in a stock, cool running motor. But I'm changing my conrods next time i tear down the engine, and my rods are probably 27 years younger than the ones in your engine. I dont remember how many hours they lasted before being replaced in the merlin engines but i think they were a bit more stressed there lol

[Dexter]

You could be right on the rods - I had no play and I knew if I took the bottom end apart it would end up doing the works and all that Castrol R would need to be cleaned up off the cases.....so I have resisted so far. I am on the look out for another set of crankcases so i can do a full build but that's going to be this winter if it happens - right now its all about riding, good luck with your build be interested what you find when it comes apart

[KnuckleShove]

I spend A LOT of time in London for work and on weekends travel around a bit. The thing I love about the UK is many still have this love of classics. I read through this thread and it was great thanks for keeping this up. What an amazing bike and adventure.