Friday, October 15, 2010

I said I want iron knees, not IRONY!

Tappet adjuster smacked the access cover a few times.
Riding home tonight can best be described as ironic, anticlimactic, and heartbreaking.
A nearby car revved it's engine at me, so I of course was obliged to return the gesture. A quick twist of the throttle, *BRAAAAAAAAAAP* the bike revs smoothly to 8000 rpm followed by a disheartening *CLACK CLACK CLACK CLACK*!
I managed to limp it home. It doesn't sound like there's anything bouncing around in there, but it doesn't sound good either.

It appears that my motor decided to throw a valve tappet adjuster and nut.
Here are pictures of the resulting carnage: (click for big)
Tappet access cover damage.
 Good tappet adjuster in rocker arm on the left,
bent tappet adjuster and missing nut on the right

Bottom is the bad tappet adjuster: damaged threads and bent shape.

Status: The tappet adjuster screw is shot and will need to be replaced. The adjuster nut is on the loose somewhere in the motor. Valve damage is unknown at the moment. There is certainly metal shrapnel in the valve train, and possibly elsewhere.
I believe my riding season may very well be over.
I'll be pulling the motor soon. This is where things get interesting.

Note: the tappet adjuster screw that went was an INTAKE, not one of the exhaust tappets that I adjusted recently.

Knowledge is Power!

My speedometer doesn't work so I couldn't tell you how fast I was going, but it felt amazing. Redline, 5th gear, passing cars like they're standing still. I'm doing all I can just to hang on to this 33 year old bike as we go screaming down the parkway. Even in fifth gear going uphill; if you grab a hand full of throttle she'll knock your fillings into the back of your throat.

The reason for this ride? I re-adjusted the exhaust valve tappet clearance after reading about the later K and F models having valve reliability issues. It seems that Honda changed the exhaust valve guide design in the later CB's to allow for longer distances between oil changes. This change however, causes the valves to heat up more and can cause the valve to gall and stick. Eventually this will cause the valve to not get out of the piston's way in time and *SMACK* there goes your valve-train.

The solution is to increase the tappet clearance by a little bit. This increase does cause you to lose some cam duration but from what I could tell by my test ride, you don't lose any performance.

Thursday, October 14, 2010

It's ALIVE!!!

She may not look like much, but I love her.
This is my 1977 Honda CB750 K7. I've had her for a few months now but she hasn't been running well until just recently. I've been chasing problem after problem since April: bad wiring, poor grounds, dirty carburetors, horrible timing, et cetera.

Fortunately for me, last night all of my efforts came to fruition. I believe I have finally sorted out most of the major problems. She is far from finished. But at least until the season is over, I believe she is roadworthy.

Sure, the head gasket leaks a little oil, the top end smokes a little bit, and she backfires some. These problems just add to her character. All-in-all she runs strong, and is a joy to ride.

At the moment the K7 is sporting a Yamiya 4-into-1 exhaust and a set of 29mm Keihin CR Specials. Next on the agenda is a little bit of suspension tuning.

Friday, October 8, 2010

My SOHC Obsession

My obsession with the SOHC I-4 engine started when I inherited a 2000 Ford Ranger with the awful 2.5L, dual plug head, single-overhead-cam, inline 4 motor.

I was forced into a relationship with this mini-truck, sort of like an arranged marriage. But we have grown to love each other very much. Sure we still have a little lovers quarrel every once in a while: I say, "get your ass up the hill" and she says "fuck you, I'm gonna shit a u-joint." However, our relationship has lasted this long and I truly believe that we will be together 'till death-do-us-part.' Which could be any day now...

To this day, the truck has never failed me. Of course by never failed me I mean, something goes terribly wrong with it about once every couple months but I manage to fix it and get on my way.
This is important: the concept that I fixed it. I have taken it to the shop for some things that I didn't have the time or resources to fix myself. But most of the maintenance and repairs have been handled by me.

The basic mechanics of the SOHC engine were so simple for me to understand early on that it was hard not to fall in love. So, here we are. I have an obsession with a mostly antiquated automotive mechanical design.

Shamelessly, I recently carried this love over into the world of motorcycles. That is, I have (almost) 2 Honda CB750K bikes that are both a work in progress. Easy to learn and maintain, reliable, and all around fun, they are the perfect first bike for me to have and start working on.

It would appear that I have fallen in love yet again with another SOHC. I'm not sure if this is considered to be the automotive equivalent of polygamy, but I sure hope no one gets jealous.