Join Date: Feb 2017
Location: St. Louis, Missouri
I remember a member in my motorcycle club calling me with a no-start condition with an older Suzuki 400 Quad. He tried 3 different spark plugs, draining the carb, tried starting fluid and who knows what else. He told me it hadnt run in 3 months, but ran great before he parked it. I had him bring it over for diagnosis.
It cranked like it had poor compression. Checking it showed 12 psi--spec was 160. A leakdown test showed compression pressure escaping from the intake--intake valves(4-valve cylinder head) not sealing.
I checked the valve clearance...and there wasnt any. Couldnt get a .0015 between the cam lobes and the shims.
Removed and disassembled the cylinder head. The intake valve faces were severely grooved, and the valve seats were badly pitted.
I asked him when he last had the valves checked or adjusted. "Never" he told me. The damage done was due to lack of maintenance, pure and simple.
He never noticed a loss of performance, it just wouldnt start. His dad told him he "probably just needed a spark plug."
I had him send the head out for the machine work with new hardened valve seats and sodium-filled valves(an internal self-cooling feature). While the head was off I removed the cylinder and piston. The piston and cylinder measured OK, a light hone took off the surface glaze. New piston rings, back on with the head, and it started the 1st crank.
So I cant agree with the idea of "You'll feel it" when assessing whether or not to check/adjust valves.
My own '99 Miata was purchased used from the original owner, a friend of mine, at 57K miles. 60K is when a valve check is called for. At 60K I checked the valves. 11 of the 16 valves were way too loose. The engine exhibited no valve noise.
I replaced/swapped shims to get them all in the dead center of spec.
The car ran great before, was much improved after the valve adjustment. Mileage increased, but the main things I noticed was quicker throttle response, and more power from midrange to redline rpm. And I was happy with how it ran before the adjustment.
I've had bikes come to me , many sportbikes. Different exhaust, mini-turn signals, Power Commander, the usual "Obligatory Rite of Manhood Modifications". I get the "I'd like more power" line. When I'd ask about maintenance, specifically valve adjustment, I'd get looks like I just shot their dog. These guys had no problem spending lotsa cash for the bolt-ons, but wouldnt do a basic maintenance procedure. I'll agree there's not as much glamour in maintenance as there is in, for example showing off a new exhaust can.
But the benefits are definitely there.