Classic Triumph Bonneville

[JackyJoll]

What can I say, I'm ahead of the curve.

Don't be jealous.

I’m as guilty of jealousy as anyone, but looking like the Turin Shroud on a motorbike is something I’d take trouble to avoid.

[David]

I just looked at the receipt again because the dates didn't seem right....it does indeed say £382 1/2, not £382.50...but the UK went decimal 6 months before this receipt was written. I can only assume it was written by someone still thinking in old money

Don't forget, back in '72 that 50p would have bought you a 3 bedroom semi-detached house.

With a new Cortina on the drive.

[Mr. Dazzle]

What can I say, I'm ahead of the curve.

Don't be jealous.

I’m as guilty of jealousy as anyone, but looking like the Turin Shroud on a motorbike is something I’d take trouble to avoid.

There are worse people to be compared too

[Mr. Dazzle]

I spoke to the mechanic today about the head.

It deffo needs new valves and springs, the former are distorted and the latter are all too short.

The head itself needs more remedial work, on top of the aforementioned ovalised guide hole the exhaust spigot threads are bolloxed due to an old repair.

As I said above, my wife's uncle seems to remember the exhausts being a problem before and he couldn't recall if the head was replaced or repaired...guess we now know!

I floated the idea of replacing the head, but his opinion is that most second hand heads you find today - the newest of which will be 50 years old - will probably be in need of some repair anyway.

[JackyJoll]

If an engineer who does old bike stuff says he can fix it, he probably can.

There can be problems though. http://www.britbike.com/forums/ubbthrea ... s/821071/2

See the little spec of light?

[Mr. Dazzle]

I wouldn't say that's a little spec of light

Mechanic is taking the head to a different specialist. He originally planned to fill and remachine the guide hole with one specialist. However if it now needs work doing on the exhaust spigot threads it's a different specialist! He's driving up there later this week with some other bike bits so we'll find out then.

[JackyJoll]

It’s littler than the port!

[Mr. Dazzle]

I took the cylinders off today and nothing fell in the casing, hooray!

The pistons have got definite marks on front and back...



And the bores look mirror shiny. There's a distinct step in the last milimeter or so at the top with loads of thoroughly baked on stuff. On closer inspection the bores have lots of vertical lines which you can see but you can't feel....



The rods have a little bit of rock on the bottom end. I dunno how much is OK. You'd expect plain bearings to have a bit of clearance....



So yeah...rebore/rehone and new pistons required!

[JackyJoll]

You can’t tell from “rock” on the rods.

It’s straight up and down play that betrays wear.

And that isn’t easy to feel unless it’s very bad.

If it has an oil pressure light, did it ever come on at idle when the engine was hot? That would probably mean worn big ends. Maybe you never got the engine hot though.

That piston skirt looks ok, just looks like a used piston.

The scratched bores are odd. Maybe the pistons aren’t as old as the bores.

You get vertical scratches on the bore when honing grit has not been washed off properly. It requires hot water and soap and a sponge and you keep washing and rinsing until the bore does not leave a dirty mark on a paper handkerchief.

There’s a strange tidemark near the bottom of the bore. Could it have been parked so long it rusted?

[Mr. Dazzle]

I think the tide marks are just from the flash on my camera reflecting from the bore. They're like mirrors.

It's entirely possible the pistons are newer than the bore, the bike had high compression pistons but these are "medium" 9:1. I believe by FiL turned the compression down cause he couldn't kick it at 11:1.

Oil pressure is fine, pretty steady at 70psi (or is it 90?
whatever the spec is) across the whole temperature range. It has no oil in the sump.

[JackyJoll]

I think the spec is 60 psi. If it’s holding that oil pressure once warm, and it still has a plunger type oil pump, the big ends can’t be worn. Triumph 650 big ends don’t really wear at all anyway, unless something goes wrong with their oil supply.

I suspected the bore photo would be a bit illusory. They often are!

But if it’s like a mirror, a coarse hone and new rings are probably on the cards, if the bores measure up ok. I see measuring bores as an expert’s job and I let the rebore guy do it.

[Mr. Dazzle]

The head is going to a specialist machine shop, they also do rebores so I'll give it to them. I don't actually know if it's been rebored before so I'll let them tell me what size rings I need.

Sorely tempted to give it back 11:1 pistons like when my FiL first bought it. For most of the time he had it it had high compression.

[JackyJoll]

Standard on late 1960s 650s was 9:1 and that is not low on a bike that you are trying to use on the Queen’s Highway.

I’m not trying to persuade you, because I know you’ll make your own mind up.

[JackyJoll]

Max factory recommended rebore was 40 thou, but that’s shit!

Unit 650s are usually safe to 80 thou oversize and people do get off with 100 thou.

[Mr. Dazzle]

Yeah 9 is standard. I just called it "medium" cause the Workshop manual has 7, 9 and 11 to 1 pistons shown.

Like I said, it was 11:1 from brand new until a few years ago. However having had to start it at a set of traffic lights a few times, 9:1 does sound a bit friendlier!

On the other hand, once it actually has rings that seal etc. maybe it will start more easily

[JackyJoll]

I will say choose compression ratio on engine performance, not on how easy it is to kick over.

[Mr. Dazzle]

Well despite it being an old Bonnie it is not a bike to potter about on. The riding position, noise and closeness of the gear ratios scream "go faster!" when you're riding it IME so far.

Of course, with a strong tailwind it might outrun a new CB500 so chasing performance might seem a bit silly. Doubly so when I also have much more modern stuff in the garage.

But at the same time, my FiL bought it off a racer when he was 22 and tore about the countryside (and a few RAF runways!) on it...

[JackyJoll]

My only gripes about the CB500 I borrowed were the very uncomfortable seat and the useless headlight. Useless in comparison to 1960s Lucas equipment- yes really!

The engine performance was great.

[Mr. Dazzle]

Holy thread resurrection! I've had other shit on recently.

The head has been delivered to the specialist and they're gonna weld/remachine the guide holes and press in new bits. The valves are pretty good, but I'll need new springs cause they're all mismatched.

The same lot are now gonna also re-hone or bore AND hone the cylinders, depending on what needs doing. I'll buy new pistons once I know what size the bore is gonna be.

Dropping off the cylinders next week.

I'm also gonna repaint the cylinders with high temp black. I need to get a tappet block removal tool first though.

[JackyJoll]

You may find they have left washing honing grit off the bores to you.