12425 - Established June, 2013 - all GRiSO, all the time...
 
HomeFAQRegisterLog in

Share | 
 

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

View previous topic View next topic Go down 
AuthorMessage
Bulldog9
Grignapoco
Grignapoco


Posts : 101
Join date : 2016-05-14

PostSubject: So lets talk valve adjustment specs...........   Wed Aug 03, 2016 8:25 pm

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.


Last edited by Bulldog9 on Wed Aug 03, 2016 9:58 pm; edited 1 time in total
Back to top Go down
ghezzi
Fra Cristoforo
Fra Cristoforo


Posts : 1699
Join date : 2014-05-22
Age : 59

PostSubject: Re: So lets talk valve adjustment specs...........   Wed Aug 03, 2016 9:09 pm

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.
Back to top Go down
http://www.biketowbrisbane.com.au
beetle
GRiSO
GRiSO


Posts : 3976
Join date : 2013-09-30

PostSubject: Re: So lets talk valve adjustment specs...........   Wed Aug 03, 2016 9:41 pm

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.




cheers
Back to top Go down
Bulldog9
Grignapoco
Grignapoco


Posts : 101
Join date : 2016-05-14

PostSubject: Re: So lets talk valve adjustment specs...........   Wed Aug 03, 2016 9:57 pm

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


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.




cheers
Back to top Go down
beetle
GRiSO
GRiSO


Posts : 3976
Join date : 2013-09-30

PostSubject: Re: So lets talk valve adjustment specs...........   Wed Aug 03, 2016 10:08 pm

Bulldog9 wrote:
In that case, maybe it's time for a map tailored to a .00 Intake and .05Exhaust lash....  affraid



Not by this little black duck. Razz



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.

Suspect




cheers
Back to top Go down
Pete Roper
GRiSO
GRiSO


Posts : 3783
Join date : 2013-05-29
Age : 59

PostSubject: Re: So lets talk valve adjustment specs...........   Wed Aug 03, 2016 11:02 pm

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.
Back to top Go down
Bulldog9
Grignapoco
Grignapoco


Posts : 101
Join date : 2016-05-14

PostSubject: Re: So lets talk valve adjustment specs...........   Thu Aug 04, 2016 8:19 am

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?  Laughing

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.
Back to top Go down
Sponsored content




PostSubject: Re: So lets talk valve adjustment specs...........   Today at 7:57 pm

Back to top Go down
 
So lets talk valve adjustment specs...........
View previous topic View next topic Back to top 
Page 1 of 1

Permissions in this forum:You cannot reply to topics in this forum
GRiSO ghetto :: The Ghetto :: GRiSOLOGY-
Jump to: