Interesting valve clearance issue

[lotus4s]

Hello gents,

After being reminded from the other cam box sealant thread, I just wanted to relay an experience I had while adjusting valve clearances on a 910 engine in hopes that it might save someone else some aggravation and also to see if anyone else had run across this before.

I am rebuilding an engine and was at the point that it was time to shim the valves and install the cam towers. I dry fitted the intake cam tower several times in order to get the clearances just right after having the valve seats reground.

Once everything was perfect with the clearances all at .006-.007, I used an aerosol spray (Permatex Surface Prep and Activator for anaerobic sealants) along with Loctite 518 to install the tower. Much to my surprise the clearances had all opened up about .003 bigger, yet the 518 thickness is supposed to be .0005. Bugger, I disassemble everything clean it up and double check everything and can't see any problem. Seal the tower again and the same thing, clearances way too big.

Now I've done the valve shim procedure many times and never had a problem so after pulling my hair out and discussing the situation with a close Lotus friend and mentor, we realized the only thing different this time was using the surface prep and activator which I had not used before.

I sealed the tower a third time without the activator and all was fine. The surface prep/activator caused my valve clearances to open up around .003 with the 518 and activator versus the dry fit measurements. It was causing the sealant to cure much faster and increasing the sealant thickness way over the .0005 specified before I could get it torqued down.

I've never seen this mentioned before so I thought I would share my experience.

Cheers,

Jim

Edited March 3, 2010 by lotus4s

[ralphw]

Jim

Have been told by our sealing specialist that Loctite 5188 is better, takes longer to cure and is more flexible than the 518. I am waiting to see his test results.

Cheers

Ralph