1987 Imola dropping valves

[Bull Tahr]

OK, so it's been a bit of a problem. Even with 1 piece after market valves. RH side as usual...... Is it the circlips and caps etc that are the problem? I have turned down some Honda XR400 valves, re-seated etc with the Honda clips etc, hoping that will fix the problem..... Any thoughts??

[Chuck in Indiana]

I suspect that the springs are the problem. You *may* be getting coil bind. Maybe progressive springs are needed? At any rate, a careful blueprinting of the head is in order.

[huub]

the springs are the problem , in 1980 guzzi used a set of springs that were way too stiff.
after 1990 they upgraded to a single progressive wound spring
comparing the two outer springs the difference is the later ones are 40% softer, with the inner spring added you are properly looking at 50% softer.
any pre 1990 smallblock should have its valve springs and exhaust valves changed.
it is a cheap modification compared to the cost of a dropped valve

i havent seen dropped valves since changing the valve springs on my ( two valve) smallblocks.

[pressureangle]

The other thing to consider is the camshaft. Pre-CNC ground camshafts have a lot more variation in profile than current production; perhaps the closing ramp on the RH side is insufficient or absent and hammering the valve on the seat. Is the RH side generally noisier than the LH side? That would indicate a harder landing on the seat.

[Bull Tahr]

Thanks for the excellent feedback. To further clarify, it's a 4 valve 1987 Imola, we have machined Honda valves and used honda springs etc, but yesterday's test ride indicated valve float, assume the Honda springs were too light...... So today's job is to replace with the original springs and modify the Honda "caps" to suit. The valves that were in it were 2 piece ones, I'm not sure if that was original or aftermarket onesincluding the springs that were in it...
Running at idle both sides seem very even with regards to the possibility of Cam problems...

[huub]

the imola 2 came with the same two springs as the two valve smallblocks , so their valves were even more prone to break than the lario,
not sure what they were thinking , fitting the same springs to a V65 2 valve and a V35 4 valve head.
i'm on the third engine in my lario.
I've got a imola2 engine with bigbore kit taking it to 480 cc stashed away somewhere,
would make a nice project.

with softer springs you are on the right track.

[Chuck in Indiana]

not sure what they were thinking , fitting the same springs to a V65 2 valve and a V35 4 valve head.

That's easy. They *had* those springs.   

[Murray]

Might be worth firing an e-mail to thunderbikes in Perth. Something about Suzuki GN250 springs but I can't remember the details.

[Frenchfrog]

Jackson racing did a whole essay here  on the 4 valve lario rework a few years ago here...extremely thorough and i would consider it essential reading on the topic.

[Bull Tahr]

I'll be looking up that Valve topic. In the meantime, looks like we are good, with the Honda Valves and stiffer springs (Not the honda ones, as they had a inner and outer set up). Bike can be seen and heard here:
https://youtu.be/I2Cxk_RTfP4

[Frenchfrog]

https://wildguzzi.com/forum/index.php?topic=98265.0