So lets talk valve adjustment specs...........

Stock valve specs on the 8V motors range from .10 mm IN and .15mm EX  to   .15mm IN and .20mm EX.

From what I have observed the gaps open .05-.10mm when the engine is fully hot, and in talking to Beetle, he recommends .10 and .15 with his maps, even on the 8V motors that the book calls for .15 & .20.

My question, if the gap opens when hot, why not run 0 lash, or maybe .025  or .05? This would limit the hammering of adjusters/stems, quiet the motor give minimally more lift and longer duration, but less wear over time and will still ensure full closure of valve.

Having some experience with the swivel foot adjusters on the 911 and 914 motors, we have discovered that we can run 0 gap without issue, and when fully hot open to between .025-  .05.  Just trying to make sense of why.  Yes I know the 'geniuses' at Piaggio spent $$$ and time to develop, and no need to get in a pissing match, just a discussion & experience.

Aside from the flat tappet issue, the so called "hammering", has never really been a problem with most engines. Basic logic says you are correct in your thinking.

Everything is a compromise, cost and ease of manufacturing, to power losses/efficiency, to longevity/reliability etc

I now wait for Roper San to chime in so I can learn something new today.

Back in the day (36 years ago) I had a Yamaha XJ650.
Set the shims myself, minimum clearance was nice and quiet.
Max tolerance was very tickety, but it had more power/torque.
Easier to pull wheelies with less duration and lift. (?) No logic there.
Unless it was to do with a higher compression PRESSURE, due to inlet valves closing earlier.

Simples. The 8V is very sensitive to valve gap changes. If you set it to something different than the 0.1/0.15 or 0.15/0.2 as per map requirements, you will fuck up your fuelling. Ergo, don't do it.

In that case, maybe it's time for a map tailored to a .00 Intake and .05Exhaust lash....

beetle wrote:

Simples. The 8V is very sensitive to valve gap changes. If you set it to something different than the 0.1/0.15 or 0.15/0.2 as per map requirements, you will fuck up your fuelling. Ergo, don't do it.

Bulldog9 wrote:

In that case, maybe it's time for a map tailored to a .00 Intake and .05Exhaust lash....  

Not by this little black duck.

Bulldog9 wrote:

give minimally more lift and longer duration

Not a good idea on an engine with altogether too much overlap resulting in charge transition issues.

Common sense dictates an element of conservatism.

Yes the gaps open up but by how much and at what temperature we can't tell for absolute certain. Yes, you can get the motor hellaciously hot and then whip the rocker cover off and measure the gap but even working as fast as possible thre will be sufficient heat soak-back to render any observation merely an approximation. Repeat the check on three different days with different ambient temperatures and I'll bet you you wouldn't get consistent results.

The results of a tappet riding the cam can be disastrous. The tappet may disintegrate due to insufficient lubrication or the valve may not seat and can burn or shed its head. You don't want to risk such damage especially when the performance gain achieved by the increase in valve lift and duration is going to be infinitesimal!

What we do know for certain though is that the 8V is very sensitive to valve timing changes, especially at lower RPM, low throttle openings but as I found on one trip where I changed them just for shit and giggles and my bike, (With Its old, dying, flat tappet motor.) ran like a bag of shit! Changed them back in the car park of the B&B we stayed in and immediately it reverted to its usual happy self.

Gotta go, the kid and his squeeze have turned up.

Thanks for the input, I'm new to MG motors, and learning. Pete, check on running the clearances too tight and riding the cam. I've been building Aircooled VW/Porsche motors for 5-6 years with solid lifters and modified valve trains with the same swivel foot adjusters. They allow much tighter clearances than the standard adjusters as the 'foot' spins and rotates between the valve stem and adjuster post. I also assumed the roller lifter would allow for tighter clearance. Man the 8V is a noisy bugger............. I kind of like it, and it makes sense on the GRiSO, but on the Norge it seems a bit out of place. Guess I have to adjust.. Loud tappets saves lives right?  

Overlap would explain the sensitivity to valve timing and lash settings. I'm currently at the book specs for the motor .15 & .20, once I get it back from MI and all the issues worked out, will adjust to .10 & .15 and reinstall the Beetle Map.  I'm waiting on my manometer to balance the TB's but MI will likely be going over all that when they try to correct the problem with the motor falling on its face over 6K - 6500 at WOT or under load.