Head issues 1970 750S

[peerfleuren]

Because of poor compression of the left cylinder I took apart the head last week:
-leaking exhaust valve left cylinder
-chrome wear on (at least) 1 rocker
-3 of 4 worn valve guides, old type

todo: serious cleaning the combustion chambers and valves, change the valve guides to brass type, grinding in the valves/valveseats. Pay Gijs a
visit to get expert advice and new parts.

any thoughts or comments?

 

[rez]

10mm Oil-pump

Regards, Rainer

 

[Paul Marx]

Go see Gijs.
Paul

 

[Laverdalothar]

Depending on how many kilometers/miles the engine has done (and how many you intend to do with it, what your budget is etc.), I would use the time to completely do the engine, including getting the crank done with new bearings and the gearbox bearings changed, too. Piet posted some pics here of what he found in crank slingers even of relatively low millage bikes. Argument enough for me to do the engine completely "while you are at it". Especially as when you fix the valves, more load goes onto the piston(s) again and therefore on the crank.

Oh - and please replace that alternator belt. It looks really like it had it's best times decades ago...

 

[Paul Marx]

10mm Oil-pump

Regards, Rainer

No point.
If you're feeling sporty, rebuild the crank doing away with the stepped crank pins. They can break if overstressed.
Guides with seals if you intend doing many tens of thousands of km.
Be careful with valve clearances.
Go see Gijs.
Paul

 

[Exmoor beast]

How many miles / Km has yours covered? Mines only done 23,000 km, which I believe to be genuine.

 

[peerfleuren]

How many miles / Km has yours covered? Mines only done 23,000 km, which I believe to be genuine.

I don't know for sure, counter says 63K, could be original... by the looks of the internals. There was no maintainance history with the purchase.

 

[Jo]

Lovely 750S! If you plan to consult Gijs anyway, I would also discuss the req'd next steps with him.

 

[Exmoor beast]

I don't know for sure, counter says 63K, could be original... by the looks of the internals. There was no maintainance history with the purchase.

That seems realistic, not that bad really when you think about it. Lovely looking bike.

 

[Laverdalothar]

If it's done 63.000km and has no real service history, I even more recommend to do the crank while nothing is yet massively wrong. Cheaper than to wait for it...

But discuss with Gijs, he for sure will recommend the right things

 

[Paul Marx]

Mine's probably done around 60 to 80 000 km. Original bores and pistons.
Head done by Phil Todd with new guides and stainless valves.
Crank done by the same Mr Todd conserving the stepped crank pins.
Was a bit of a mess when I bought it.

Paul

 

[Gerald]

Lovely looking bike. Are you sure it's a 750S? Tank looks like a 750 SF flip top vs. the screw on tank lid 750 S. Engine seems tired, take it to Gijs.

 

[Paul Marx]

Lovely looking bike. Are you sure it's a 750S? Tank looks like a 750 SF flip top vs. the screw on tank lid 750 S. Engine seems tired, take it to Gijs.

It's an S frame.
Paul

 

[peerfleuren]

Lovely 750S! If you plan to consult Gijs anyway, I would also discuss the req'd next steps with him.

I sure will

 

[peerfleuren]

Lovely looking bike. Are you sure it's a 750S? Tank looks like a 750 SF flip top vs. the screw on tank lid 750 S. Engine seems tired, take it to Gijs.

Original late S, some SF features already on it, frame/engine nr 3730

 

[peerfleuren]

It's an S frame.
Paul

Lovely looking bike. Are you sure it's a 750S? Tank looks like a 750 SF flip top vs. the screw on tank lid 750 S. Engine seems tired, take it to Gijs.

52 years old, condition oké exept for leaking valve and poor compression on one cylinder…

 

[peerfleuren]

Mine's probably done around 60 to 80 000 km. Original bores and pistons.
Head done by Phil Todd with new guides and stainless valves.
Crank done by the same Mr Todd conserving the stepped crank pins.
Was a bit of a mess when I bought it.

Paul

Lovely bike Paul!

 

[Paul Marx]

Lovely bike Paul!

Thanks. A bit of work to get there but I use it quite a lot now it's sorted.
Numbers near yours I think.
I'd need to look.
Paul

 

[peerfleuren]

Did some cleaning today, inlet valves and seats look fine imho, outlets however…
Any comments?

 

[piranha-bro2]

Inlets OK. Exhaust will be too thin by the time the pitting is gone. I'm a huge fan of otiginal cast iron guides in SFs. If the top end is receiving oil as it should there should be zero wear on thew guides. Whoever builds it must check that the oil is getting to the rocker spindles - can be blocked by the heads studs fouling the groove through which the oil then flows to the rocker spindles and onto the cams - then flung about.