Classic Triumph Bonneville

[JackyJoll]

That several decades probably extends to 'ever'.

They came new with pre-worn valve guides.

[Mr. Dazzle]

That several decades probably extends to 'ever'.

They came new with pre-worn valve guides.

And self loosening bolts.

As for ring gaps ....that particular can of worms is one I elected to not open. j just let the guy who makes a living fixing Brit iron decide!

[Rockburner]

shouldn't that mating surface be a bit smoother??


Nice job otherwise.

[Mr. Dazzle]

It's smoother than it was

It uses a really thick copper head gasket so probably doesn't matter.

I'm more curious to know what the +0.01" stamped on the cylinders refers too. Maybe they've been machined down to get a flat face again?

[JackyJoll]

0.010” oversize pistons for Triumph 650s do exist, but they’re not mainstream. A worn Triumph usually needs more than that taken out of it.

I believe I’ve read that the factory took badly bored new barrels out to +0.010” and put them in new bikes. It would make sense to mark the barrels so they were fitted with +0.010” pistons.

[JackyJoll]

....

[JackyJoll]

shouldn't that mating surface be a bit smoother??

And the edge of the combustion chambers actually looks rounded. That’s very strange.

Edit: Apparently normal according to Google Images. Wonder if it’s their attempt at a squish band.

My cast iron one has a sharp edge.

[KungFooBob]

The valve to sparkplug hole gap doesn't look very symmetrical across cylinders, is it supposed to be?

[Mr. Dazzle]

I've noticed the same thing about the plug holes before. I've just had a look though and it's a trick of the photos I reckon.

But from what I can tell the valves should not overlap the plugs at all. Knowing this bikes racing past I'm wondering if its got big ports/valves? Standard head:



There's also a distinct chamfer around the edge of the chamber as people above noticed. Looks intentional.

[JackyJoll]

The valve to sparkplug hole gap doesn't look very symmetrical across cylinders, is it supposed to be?

Looks like metal has been cut away to expose the edge of the valve, when the seats were recut. In a perfect world, they would be identical, but it shouldn’t matter. It could cause a variation in compression ratio, between the cylinders.

[JackyJoll]

The combustion chamber volumes, and thus the compression ratios, could be made identical by removing metal from a piston.

I think that’s the sort of behaviour Americans used to call “anal” though.

[Mr. Dazzle]

Well the amazing resource that is the old boys on Triumphrat.net have revealed its a post 71 head. The give away is two small extra holes in the rocker box mating faces. My FiL bought the bike in 72, we also think it may have had a new head at some point, but we're not sure. I believe the nominal "squish band" around the edge may be a newer post 69 feature too.

Current challenge is finguring out what combination of tappet blocks and push rod tubes I have/need. At the moment I've got two slightly different ones.

I'm getting together the list of seals etc that I need and unfortunately the PRTs effect that.

[Nidge]

The PRT on the left looks like it still has the “wedding band”, as fitted to later engines, still attached at the bottom. They can be quite a snug fit but should pull off. You’d still have two different PRTs but they may be the same height once removed

[Mr. Dazzle]

Yeah I've got the wedding band from the other one loose in a box. Its stuck to the one on the left with gasket goo

Theyre different at the top too. I haven't looked in detail yet but I'd not be surprised if the tappet blocks were different.

[JackyJoll]

The serious pushrod tube leak problems started in 1956, with the alloy 650 cylinder head. Earlier ones had the pushrod tubes mated to the rocker box and had external oil drain pipes.

To do away with messy-looking drain pipes, the pushrod tubes were made shorter and mated to the head, low enough that the oil could drain straight into the pushrod tubes.

The old drain pipes on the iron head did develop the occasional leak, but were accessible and easy enough to fix. The pushrod tubes too, could be accessed by removing their respective rocker box.

A pushrod tube leak with an alloy head can be tricky to deal with, as you have to remove the cylinder head, disturbing both tubes, to reach one tube. Also, cylinder head and barrel top height is critical. Once the head has been skimmed, you have to go non-standard with rubber washer thickness to get the right crush. I think it’s about 30 thou, but you would be wise to check.

Gasket sets come with two alternative thicknesses of rubber base washer, which confuses the home mechanic.

[Mr. Dazzle]

I need to get back on this bike. I've been a bit meh about it for a while, combination of the garage being stacked full of crap and ongoing family issues.

But anyway....the last outstanding bit of this bike which requires outside help (I hope!) is cleaning up the rocker boxes. I was in two minds about doing it before, I've heard from a few places that if they work they're best left alone.

However, the head is all fresh and clean after being machined, so the rocker boxes need to be clean otherwise they'll be horribly mismatched! I've found a place 2 miles down the road who do powder coating, grit blasting and vapourmatting for classic vehicle restoration. First job of course is to disassemble...



And as expected I found a couple of bits not quite right. Namely, the adjusters on the rockers don't match. The one on the right is OE Triumph AFAIK, the hex drive on the left is something else.



I just know getting all the springs and washers back in is gonna be an absolute twat. I also need to consult the oracles/gods/tea leaves as to which kind of washers and springs I should be using.

[Mr. Dazzle]

I tell thee what, for such a simple machine this bike ain't half a minefield of complexity!

Current dilemma is what seals to order. I'm buying a load of stuff to put the cylinders, head and rockers back together. Triumph seemed to have changed their mind every 6 months and BSA throw an occasional spanner in too. I also think this bike has newer rocker arms.

Net result is that the order of springs and washers during assembly of the rockers suddenly becomes massively important aparrently.

[JackyJoll]

There is an issue with how the plain washers and Thackeray washers are assembled. I’ll do some research.

[Mr. Dazzle]

I wouldn't, unless you wanna dissappear down a rabbit hole.

Thackeray washers only slightly less contentious than running in procedure or oil type from what I can see

My only really decision is do I put it back together as found or should I upgrade to the mid 70s superior oiling rocker shafts with grooves.

Edit: really clear explanation here.

http://www.chopcult.com/forum/showthread.php?t=55231

[Mr. Dazzle]

Right, so my bike has rockers with a 'notch' in the end, said rockers seem to have been designed in 1968 but actually introduced.....who knows when.

The rockers run on a hollow shaft which is fed with oil, little holes in that shaft feed the 'bearings' the rockers run on. There are no bearings, the rockers just run straight on the shaft with said oil to help.

The two rockers sit where the dark gray slimmer bits are.

The rockers are notched so that oil can escape from under them and then get to the valves and pushrods via splash. The guys who added the notches to the design in 68 also intended for there to be a groove in the shaft as below so that oil had an easier route out from under the rockers. For some reason that groove never appeared on 650s and only hit production in 1973 on 750s. However they do fit in the 650s - indeed they were designed for the 650 - so maybe I should get them.

Triumph DID issue a load of service bulletins around washer size and order of assembly.