Chronic Tight Valve Part 2

[norustscott]

To refresh memories..

I had an intake valve act up and get tight after only 100 miles post adjustment...it continued this cycle three times before I got nervous and pulled the engine and heads and sent them off to RIMCO for new seats. I reinstalled the engine and after three hundred miles the same valve...intake 4...began to do the same thing. Tight to the point the valve is open and the adjuster has zero clearance.

saga continues...engine back out...heads off...

Well, I have disassembled the heads...and have measured and re-measured every aspect of the valve. The verdict, It is not the valve.

I just got off the phone with RIMCO...As I figured, little to no help. 5 thousand miles is a big hurdle. Todd at RIMCO wished he could be more help. told me I should continue to monitor and measure. Not exactly an easy job on a 914. Measurement = Remove engine.

I have new intake valves on the way. I will lap them to the new seats and do a solvent leak test...

A couple of questions for the board.

I noticed that on intake number 4 the keepers have some play in the direction of valve movement. The keeper grooves are not burred. Typical? Can this cause the valve to get tight? Am I grasping or what? Would you spot grind the keeper edges for a tighter fit? They actually touch when installed around the valve stem.

My thought process and inspection results so far

1. Cam shows zero wear problems. If cam where a problem I would have the same problem on teh other side of the other side of the engine
2. Lifter, Solid not hydraulic. Pulled and inspected FLAT no signs of wear
3. Push Rod. Straight stock length equal to others. Same material as others
4. Rocker arms, stock no signs of galling or wear
5. Adjusters. Fist occurrence was with stock 8mm Second time with MAZDA ball swivels. Went to switch to original 911 adjusters. would not fit @ number 4 intake. This is with the rocker faces spot ground for clearance .150"
6. Valve. 116.7mm .3127 diameter
7. Seat. New. from the famed Riddle Machine Company

My next test is to compare intake 3 to intake 4. Put 3 into 4 adn visa versa. Mearsure the amount of stem protruding from teh rocker side of the rocker side of the head. do this for 1 and 2... This will tell me if the seat in #4 is lower in the head than the others...
sound right?

What to do next? Put back together with new valves and pray. Your continue thoughts and Idea are appreciated.

[John Rogers]

Over the past couple of years we went through a lot of testing and trial and error with my race engine as I was breaking exhaust valves at an alarming rate. here's some of the things we checked and or did: made sure the halves of the keeper did not touch, measure all valve stem heights to match, measure springs open and closed pressure and match within a couple of pounds, use dual springs, 110# close, 320# open pressure at 0.545 lift, titanium retainers, titanium valves ($$$$$$), hardened seats with high crush pressure, larger guides (Chevy size), run race (110) gas with MSD ignition for clean burn, set valves hot (as Crower said to do) and use 14gm ea drag racing push rods. Whew, we had lots of testing and finally made it through 3 races w/o troubles. We pulled the heads this winter and noted several exhaust seats were sinking into the head and the header stubs looked like they were burned from too lean, but the plugs and O2 meter said the mixture was just slightly rich. A talk with MSD noted we were probably running the timming with not enough advance (we have 34 deg) and they said with the 100 or 110 gas we could go up 4 to 6 degrees and the mixture would stop buring as it went out the exhaust and overheating the valves and seats. So we are going to the dyno next week to see exactly what we have to do with thermocuples on each exhaust to monitor things. I'll post the results when we get finished up.

The Union 76 rep told me that 100 octane was a heavier gas but had additives to help it burn faster and that 110 was lighter and as such would go through carb jets slightly easier but the end result was the mixture would be about the same for either using Webers or other "old" technology!

Hope this helps some?? Good luck.

[tryan]

i would send the head to rimco via yesterday air. you'll have it back before that three feet of snow melts.