Tappet rattle which isn't

[Paul Sutton]

I ordered a couple of VW lash screws and they arrived today. I immediately noticed that they do not have polished hemispherical ends, they are closer to conical and bear the marks of being turned and are not polished. I gently ran a file across the ends and it cut in where as the original XS tappets are hardened and a file will slips off without leaving a mark. So what is the story with lash screws? Is it not necessary for them to be hardened?



It is my feeling to return the lash screws unused, or is the level of hardness required quite subjective?

Thank you for any views/advice.

 

[Michaelo]

Hmmm, I have never heard of the adjustment screws being soft, i'd be asking what the Rockwell hardness is on them from the manufacturer, link to hardness scale. we use this all the time at work....

https://en.wikipedia.org/wiki/Rockwell_scale

 

[TwoManyXS1Bs]

Paul, I'm very proud that you had the presence of mind to inspect and hardness test the tips. I'd say you got burned.

It is so easy to pass off inferior products when hardness and heat treatment is skipped. A real problem in the hobbyist-machinist arena, with budget import stuff.

 

[xjwmx]

The ones I've gotten from Advance were polished and have lasted a long time. But I think Advance doesn't carry them anymore, not in the system. Might try other auto parts stores. Probably a VW or Yamaha dealer would be one way to go. The VWs I got were identical to yams, only diff that screw slot.

 

[Paul Sutton]

Thank you everyone:

TwoMany, I followed the advice regarding testing for hardness you gave in a thread about 2 years ago when you discussed regrinding lash screws - Thank you.
Xjwmx, thanks for the help. You did mention that you had heard negative comments regarding after-market screws so that is why I tested them with a file. I plan to go direct to a VW Dealer as you suggested.

I took all 4 tappets out two weeks back, the left-hand screws were both polished like a mirror but pitted and there was a scuff mark on the exhaust valve which I take to mean the valve is not rotating. The right-hand screws were not pitted and not polished like a mirror. I will be pulling the motor in the next month to overhaul the top end and check why the exhaust valve is sticking. Will replace all seals, do a valve grind and inspect all oil ways.

I read on a car forum not to mirror polish tappets but just buff them up with a bit of wet and dry greater than 600 Grit. The reasoning was that the mirror finish will not hold oil as well. Perhaps this is in part the reason for the pitting on one side??

Are original Yamaha lash screws mirror polished or just buffed?

Thank you.

 

[TwoManyXS1Bs]

...TwoMany, I followed the advice regarding testing for hardness you gave in a thread about 2 years ago when you discussed regrinding lash screws - Thank you.

Yew betcha, Paul.

...I read on a car forum not to mirror polish tappets but just buff them up with a bit of wet and dry greater than 600 Grit. The reasoning was that the mirror finish will not hold oil as well. Perhaps this is in part the reason for the pitting on one side??

I agree on "oil retention" for sliding surfaces whose only replenishment is thru surface adhesion, like for automotive "zero lash" hydraulics. Our tappets have clearances, which allows replenishment.

A thread topic I was considering, the relative sizes of oil molecules versus surface roughness, and the 4 boundary layer thicknesses. Sigh, sometime.

...Are original Yamaha lash screws mirror polished or just buffed?

Dunno about Yamaha, but period Honda screw tappets were buffed just shy of mirror...

 

[Paul Sutton]

Thank you TwoManyXS1Bs, it all makes sense. I will proceed with my top-end work once my compression tester arrives so I have a reference point on the condition of rings/valves etc. I have contacted a genuine VW parts supplier and returned the after-market screws today.

 

[aldo5468]

Another option with well-proven motorcycle service is Yamaha P/N 4X7-12159-00-00, used 13 years in large Viragos and 15+ years in Star 110's and 950's. They are just slightly shorter than stock 650 adjusters and have female hex instead of screw slot.

 

[Paul Sutton]

Aldo5468, excellent - I will look them up now. Hex is are much easier to adjust than the square tappets.

Thank you.

 

[Paul Sutton]

Found a seller on Ebay selling genuine VW parts. I ordered a couple of tappets and they pass the file hardness test. They cost £6 whereas the cheap knockoffs were £4.50.

 

[5twins]

If you have the head apart, I feel a better option are the elephant foot adjuster screws. They can only be installed if the head is apart because some rocker grinding is required.

I feel the original design is poor. The rounded tip of the adjuster screw only contacts the valve stem in one tiny spot. The screws routinely wear out and sometimes the valve stem tops get dimpled too. New screws are only a temporary solution because they'll eventually wear out too.

 

[geedubya]

Just brilliant doing the VW tappet cross-reference thing, Paul. Thanks for the info! I adjusted a ton of those things in the 1970's in my beetles, Karmann Ghias and a 60's bus.

The Cardiff Giant of New York State was dug up just a few miles from my home; I ride by the spot regularly. Then they eventually moved it to Cooperstown, NY, for museum purposes.

Here's a pic of one of my Ghias that I bought as a rust bucket. Lowered, sculpted, painted Porsche Guard Red:

View attachment 98207

Dude,

G'day mate. That Ghia looks the biz. Would be worth a fortune now.