Topic: New project- Guzzi NTX650

[BenelliSEI]

Did he suggest why the valve failed?

[simon#42]

Two piece valves do this , the joint can crystallise over time and the head falls off . Have seen this on the bigger guzzis but have never had much to do with the small ones .

[Tim2005]

I suspect the cause will never be known for sure. I wondered if it is to do with the bike sitting a long time, I think it must have been parked up for 15+ years, maybe corrosion could have got into the valve stem joint. 

All the bits have arrived so I now have a small jigsaw to sort out over the next few days.

I notice the exhaust headers are quite pitted, see photo. I've cleaned them up and treated them with rust killer prior to painting them black, but can anyone suggest anything that could be used to fill in the pitting? I'm not keen on grinding it out as they aren't all that thick & would be very hard to replace

[MRieck]

It's not good. As I figured a strip down was essential, it was even no longer possible to remove the right pot's spark plug, that one undid perfectly well last week & was suddenly stuck. Draining the oil didn't reveal much at all though, no glitter, so that is positive. Anyway, off came the exhaust (easy enough) and the carb (awkward but ok) and then the top end. It is very simple to dismantle this, it's a pushrod motor with overhead valves so very straightforward.

Well, it used to have overhead valves. As you'll see from the photos it now only has 1, the top of the other had dropped off & wrecked the piston & head. The cylinder survived ok luckily. I'm currently on the hunt for parts. Secondhand cylinder heads are reasonably available, but it is at times like this I realise how good we have it in the Honda world, if this was a Honda I could call up David Silver's, or others, and get a choice of new pistons in various sizes. For a vintage Guzzi there are no new pistons available, nobody supports them, so I'm actually having to buy a used piston for it...

That chamber can be salvaged. I've repaired worse than that with more complex shapes. That being said....it very well may be cheaper to find a good used one. The ones I have done had a lot of porting etc in them.

[BenelliSEI]

I once had a set of pitted pipes “ceramic coated”. They were the original pipes on a 1957 Lotus Eleven I raced for many years. It improved their appearance 100% and the coating lasted forever. It was ages ago, so this may have changed, but I recall it was pretty expensive.

[simon#42]

There is a firm that ceramic coat parts in warrington tim .i had some piston crowns done but when i collected them they had exhausts that they had done and they looked good .

[Tim2005]

I'd be surprised if it is salveageable but it'd be worth having a spare around as parts are so rare. There's one big gouge next to the inlet in particular that seems to have actually moved the valve seat in the head, it chewed up the spark plug thread too. I'll see if I can get a photo later.

Thanks for the ceramic coating idea, I'll look into that. I'll just paint them for now to keep the weather away, my plan is to get it back on the road shortly (should only be a few days now as all the have bits arrived) and use it until spring so i can make sure the rest of it is aok. It always was intended to be a winter bike. In the summer I want to repaint the whole thing, with an idea of doing something along the lines of Fabrizio Meoni's Gauloise colourscheme, I can send the pipes off for ceramic coating while I'm doing that.

[MRieck]

I'd be surprised if it is salveageable but it'd be worth having a spare around as parts are so rare. There's one big gouge next to the inlet in particular that seems to have actually moved the valve seat in the head, it chewed up the spark plug thread too. I'll see if I can get a photo later.

Thanks for the ceramic coating idea, I'll look into that. I'll just paint them for now to keep the weather away, my plan is to get it back on the road shortly (should only be a few days now as all the have bits arrived) and use it until spring so i can make sure the rest of it is aok. It always was intended to be a winter bike. In the summer I want to repaint the whole thing, with an idea of doing something along the lines of Fabrizio Meoni's Gauloise colourscheme, I can send the pipes off for ceramic coating while I'm doing that.

That's not a problem to fix with aluminum....may need an insert for the plug hole.

[Tim2005]

Quick update- the engine rebuild is progressing well, with a slight delay as the top end gasket kit does not include the gasket for the inlet manifold, so I've had to order it separately - only £1.50 but another few days wait and £4 postage annoyingly.
Meanwhile... the replacement cylinder was actually freshly vapour blasted and cleaned and ready to use, so very smart looking (unlike the rest of the bike....) but I thought I'd give it an extra clean just in case. I let it soak in a tub of petrol/gas overnight, with a few shakes,  and there was definitely a little fine sediment in the bottom after. I've given it an extra cleaning through all the oilways etc too now. I don't generally like engine parts being blasted, I am now pretty confident this is clean but I think I'll give it an oilchange after it has run just a little.

[simon#42]

a bit late to add this after you have put it all back together but I would have changed the valves before I assembled it . The aftermarket ones are one piece and would prevent a repeat of your problem . Same for the other cylinder .

[Tim2005]

Yes that was my plan too, but neither of the UK specialists were able to supply valves, they both said that valve problems on the 2 valve small block engines aren't a known thing, it's the 4 valve ones that usually have the problem, so they haven't sourced them. 

I have since spotted that Stein Dinse in Germany list them, though 2 different types without explanation (one at €25 and one at €140), so I'll look into them. Getting the heads off is a very straightforward, I can do them when I have the motor out for the bike's paint job in the spring

[simon#42]

yes the joy of twin cylinder bikes whose cylinders stick out is top end repairs are easy .

[Tim2005]

It is time I posted an update on the Guzzi. Well the engine is back together and running well, after an initial test run I gave it an extra oil change to pick up any leftover pieces of piston or valve, then took it for a good ride out one day last week for around 100 miles. The engine has an odd power curve, it is really lively up to about 3500 rpm then just flattens out when I expect it to keep building & get exciting. I do forget it's only a 650 though.  The rest of it works ok, though I want to try to improve the tickover/low down running as it has some issues there, I just needed some different vacuum gauge adaptors as the manifolds have M6 threads & my gauges have smaller ones, I've found some online & they've just arrived. Talking of threads, clutch adjustment has been awkward, the bar lever end was missing a locknut, which turns out to be the unusual size M8 x 1.0mm, I've bought a normal nut & slotted it for now but would like to get a proper round adjuster for it, meanwhile the pushrod adjuster & locknut is at the back of the engine & access to it is completely blocked by the swingarm. 
Meanwhile, I have also made progress with the wheels, I found a pair of old rims and had them anodised gold, got some new spokes from Italy and have have rebuilt the front wheel, which was the worse corroded rim.  I repainted the hub while it was stripped out too, it now makes the rest of the bike look rougher ...

[BenelliSEI]

Well done! Such an interesting motorcycle.