Re­build­ing to ride

Things have moved on a lit­tle and there’s news of the next project too.

Classic Dirtbike - - Contents - Words: Tim Brit­ton Pics: Tim Brit­ton and Fiona Wat­son Box-out: Jerry Thurston

Rapid progress has been made on the bits of our Project 90, a lot of them are in and where they should be.

Aflurry of ac­tiv­ity has re­sulted in the project Tri­umph frame hav­ing a coat of ad­mit­tedly ‘rat­tle can’ black (but at least it looks ti­dier), some stain­less steel from Andy Mol­nar and a few more pieces from Bur­ton Bike Bits. The engine is now as­sem­bled, okay so the gear­box isn’t in yet but at least the cases are all to­gether and the engine turns over. The cause of such ac­tiv­ity? Find­ing a restora­tion of a Tri­umph TR5A/C on the in­ter­net, it looks so good I’m de­ter­mined to have an as­sem­bled bike to work from.

Qui­etly one evening I played the blow­torch over the cast­ings so the bear­ings and var­i­ous hol­low dow­els could eas­ily drop in. The old method of de­ter­min­ing when a cast­ing is hot enough for such things to hap­pen – spit­ting on it and if the spit bounces off you’re good to go – is okay but I was shown an­other method some years ago which works for me. There’s this big hole in the cast­ing, a bear­ing to go in it, I’ve a cheap pair of calipers – se­ri­ously cheap at 75p years ago – mea­sure the bear­ing, heat the cases, the in­side points are set at the bear­ing di­am­e­ter, when they rat­tle about in the hole the bear­ing will drop in. While I was at it the hol­low dow­els went in too and I left it overnight to cool down. Overkill? Yes, but I’m not run­ning a restora­tion busi­ness where time is money.

Next day the sludge tube was fit­ted into the crankshaft and the end plug screwed in, it only took two goes to line up the lo­cat­ing hole for the fly­wheel bolt to hold the tube in place. Pump­ing the crank full of oil and fit­ting the con rods is a very sat­is­fy­ing process, as is slid­ing the drive shaft through the bear­ing in the drive side case.

Ac­cord­ing to the man­ual the cams should go in the drive side case too and the tim­ing side slipped over the top. This was the first hurdle to over­come as try as I might this couldn’t hap­pen. Luck­ily, the cams run direct in the case and it’s pos­si­ble to feed them through their bear­ing holes. It makes lin­ing up the breather disc tricky but not im­pos­si­ble. A light smear of liq­uid gas­ket and the cases went to­gether eas­ily, the pre-sized bolts were on hand and ev­ery­thing nipped up, the crank even turned rea­son­ably eas­ily too.

The pis­tons I have are from a 1967 T90 and are 9.5:1 com­pres­sion ra­tio… this may well be a lit­tle high these days but in the Six­ties 5-star petrol was avail­able at quite a lot of petrol sta­tions. Will I end up us­ing them? Not sure, there is an op­tion of a

com­pres­sion plate un­der the bar­rel at some point and there are for­mu­lae to work out how thick a plate should be to give a lower ra­tio. Even the ear­lier T90s had 9:1 but I’m think­ing more 8:1 for the use I have in mind. So, the pis­tons, a light warm­ing with a heat gun and in went one gud­geon pin as the pis­ton was lined up with the con rod eye, the sec­ond one wasn’t play­ing ball at all, it liked be­ing on the bench and was de­ter­mined to stay there. It went in even­tu­ally, quite eas­ily…

Most of us delv­ing into en­gines will re­alise drop­ping some­thing into the crank­case when it’s to­gether is bad, most of us will use some method of cov­er­ing the crank­case mouth in case a cir­clip is dropped. I use the cloth method and in how­ever many years since I first lifted the bar­rel on an engine to change a lit­tle end bear­ing or rings or some­thing the cloth has never been needed to save the day… un­til now. Pesky lit­tle cir­clips re­fused to go in their groove and two of them dropped onto the cloth. Still, they’re in place and the pis­ton rings too af­ter check­ing them in the bore as a pre­cau­tion.

Now, I know you’re sup­posed to use pis­ton ring com­pres­sors to close the rings up for the bar­rel to slide on but I don’t have any the right size so used a more or­ganic method of care­fully plac­ing the bar­rel on the pis­tons and com­press­ing each ring by hand… feel free to write in. in any case the bar­rels are now in place, the pis­tons go up and down and some nice new stain­less steel nuts and wash­ers hold them in place. The fun task of sort­ing through the bag of pushrod tube seal­ing wash­ers still awaits.

A job I’ve been putting off is to as­sem­ble the rocker box I took apart for no other rea­son than I wanted to pol­ish the al­loy. All the bits are there but I re­call last time I did the assem­bly on such a thing it was a night­mare to try and line up the shims, springs and rock­ers… this time though it went sur­pris­ingly easy.

Gear­ing up

At this stage there’s an engine on the bench in the cra­dle and there’s also space on the bench to lay other things out such as the gear­box. The gears are in good con­di­tion but the high gear bush has split but my spares box has a high gear with­out a split and that’s the one now with the other cogs. Once they’ve been washed thor­oughly in the parts washer, rinsed, dried and oiled they will go back to­gether.

It’s pos­si­ble to make all sorts of clus­ters up thanks to the va­ri­ety of cogs pro­duced by Tri­umph and some af­ter­mar­ket ones for the tri­als scene but stan­dard is the way for­ward at the mo­ment. There are wide and close ra­tio clus­ters out there as op­tions and clever peo­ple can tai­lor a clus­ter to al­most any need, how­ever that seems a lit­tle ex­ces­sive for my needs with this bike. Maybe once it’s to­gether and I’ve rid­den it – that’s ac­tu­ally a pos­si­bil­ity now – I’ll find I can’t live with­out drop­ping the bot­tom gear much

lower and fit­ting the close ra­tio third and maybe I won’t.

I’ve had to steel my­self a lit­tle and will be re­plac­ing the badly hooked drive sprocket on the shaft just for the time be­ing, though think­ing about it I don’t need to put it on to as­sem­ble the engine fur­ther, so maybe it will stay in the box where we put things we’re not go­ing to use but can’t bear to chuck out. Once the clus­ter is in place I can fit the clutch and things will start to look up a lit­tle. Be­fore that though, there’s a hol­low dowel to re­place in the gear­box in­ner cover, it got mashed on the end some­how and it is a through dowel. As such it needs set­ting in place cor­rectly. So a bit of heat on the case, the old dowel pulled out, the new dowel with a smear of grease is in­serted in the hole, a dis­tance piece the cor­rect thick­ness hung over the end and a bit of tube, or an old socket ac­tu­ally, put over the exit hole, a few turns of the vice han­dle and the dowel is set in place.

Be­fore all is as­sem­bled I’ll lap the clutch hub onto the main­shaft ta­per so it seats prop­erly then it can be washed off and when the time comes to as­sem­ble it we’re good to go. I will need to get a new pri­mary chain, it’s a du­plex and will need to be fit­ted in one go with the front sprocket and clutch drum, a task which I never look for­ward to as there are so many po­ten­tials for the roller bear­ings to drop out, or the Woodruff keys to drop...

In the frame

One af­ter­noon in the sum­mer, I set up a stool out­side, fit­ted a wire brush to my an­gle grinder and re­moved as much of the paint and rust as I could from the main frame, sub frame and swing­ing arm. I was quite pleased with this method though even­tu­ally the frame will be blast cleaned and prop­erly painted, but this will do for the mo­ment as there will be the odd bit of brack­etry to go on and un­til the dry build is com­plete I’m not sure if

there will be weld­ing to hap­pen too. So, while still in bits, the bits are big ones and will be as­sem­bled eas­ily. I’ve forks to sort out though and have op­tions there too, the eas­i­est method would be to bung the orig­i­nal forks back in but I can only find one slider at the mo­ment. I do have sev­eral sets of BSA forks which are for big­ger stan­chions than Tri­umph used. These would fit the ethos of the build but not the bot­tom yoke as it would need to be opened up by a few mil­lime­tres which would weaken it and de­feat the ob­ject of putting stronger forks on.

The search for the miss­ing slider goes on… it will be there.

Above: Just be­fore as­sem­bling the crank and cams, there was a dry run to make sure all the studs and bolts were on hand.

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