Zero Valve Clearance

[spub]

I checked the valve clearance on my 3 1/2 Sport over the weekend, and while the rear was fine at .10mm, the front had zero clearance. I attempted to adjust it but found it would not adjust it for any clearance (even with the adjustment screw fully backed out). I pulled the rocker assembly and checked it, fine, and checked the pushrods, all in good order. Checked to see if head and base gaskets were installed, and yes, there they were. Head itself appears not to have been milled down, appears same as rear, so I'm thinking valves have compacted into seats? Before I pull the head, has anyone ran into this issue?

[Steve Brown]

Yes, it happened to one of mine years ago, but that was a replacement valve seat that had come loose and was being hammered back into the head. Not a very good seat replacement job.
The other alternative is valve seat recession and if that's what it turns out to be the whole Morini world will go in to panic worrying about leadfree fuel!
See that can of worms over there?

[EVguru]

VERY IMPORTANT INFORMATION MISSING!

Which valve, exhaust or inlet?

[Steve Brown]

VERY IMPORTANT INFORMATION MISSING!

Which valve, exhaust or inlet?

S'easy! the tight one! Keep up Paul!

[spub]

Both. Neither Exhaust nor inlet had any clearance. After taking apart, looks like if Rocker blocks were shimmed up perhaps .3mm, you could get some clearance, but both have zero. That is why I am puzzled, seems unlikely both would compact at the same time. Almost as if someone inserted longer pushrods, different rocker blocks, valves with longer stems or different rockers....or a combination.....

[spub]

By the way, thanks Steve and Paul for posting suggestions...

[EVguru]

Now, off the top of my head, which is the longer set of pushrods, front or rear?

It's just possible they've been swapped, or two sets of long rods installed.

I'd grab the book and have a look, but I'm under a cat at the moment.

[Steve Brown]

As Paul suggested, the front pushrods are approx 2mm shorter, that would do it. (I had to look in the book to be sure too)

How big is that cat, Paul?

[EVguru]

How big is that cat, Paul?

Quite small, but with VERY sharp claws!



She's the one on the right.

[Steve Brown]

@Paul; My wife says Aahh! But how big is the one they're sitting on?

To get back on topic, as it was me what wandered, is Spubs bike fitted with a Cat?

[hendre]

wasn't there also something with the rocker block beeing mounted wrong side up? the stamped A must be on top otherwise your clearance is also limited?

[spub]

Thanks for the replies. Blocks with "A" facing upwards, so that is not it, although I did try reversing, and no luck. I believe there are only two possibilities now, either longer pushrods inserted by PO, or both valves happened to compact...given that inserting a thin washer allows me to gain the property clearance and the rear pushrods are 2mm longer, that is a good possibility. Can anyone please post, if handy, the length of the front pushrods so I can measure the ones I have? Thanks.

[EVguru]

Valve seat recession due to unleaded fuel only really happens (if at all!) on exhaust valves, which is why I asked which one was giving trouble.

Given that it's both valves and everything else appears to be ok, then perhaps someone has re-cut the seats on the front head and sunk them a little too deep in the head.

[spub]

Paul: That is certainly possible, and I guess either possibility is as likely using Ocam's Razor (the simplest explanation is generally the correct one). Before I go through the hassle of tearing off the head, I'm going to try a set of front pushrods from NLM, which they are sending, since I suspect this is the most likely possibility. Worst case, I have an extra set of front pushrods and still have to yank the head and send it out, best case, I am done without having to hassle the new head job. I just don't like taking apart perfectly fine gasketed surfaces if I don't have to...

[spub]

and I would still very much appreciate it if someone could post the length of the front pushrods...