Topic: Engine locking up - What should I look for? - Fixed...

[KB02]

So I was finally getting my Cam timed in. I got the Webcam 41A set to open at 27 degree BTDC. I was down to the last cylinder getting all the valves set at .040 and all of a sudden the engine would not turn forward anymore. I tried turning it backwards, but I am only able to turn th engine one full rotation. It's like something is blocking it from turning any further. I looked everywhere I could down from the top end but could not see anything.

What should I be looking for?

It's lunch time, so I'm taking a little break from the heat and eating some pizza. I'll go back out after lunch, but I'm really at a loss. It had been turning fine all morning long.

[honda750k]

Your cam timing is off and one or two of your valves are touching a piston at TDC

[KB02]

That's the first thing that I though of, too, but I checked all of the valves and the only one that is open enough to hit is actually closing at the time of the hit. I'll double check, though.

[KB02]

Okay. You were right, it was a valve. I loosened up all the tappets and the engine rolls again. Looks like I was off by a big a mount. I reset my timing sprocket and now I'm just a little bit retarded... the timing... not me... I'm a lot retarded...

This is what I'm after:

I saved mine...

Valve lash:  Intake .004 Exhaust .004
Lift:                     .360            .360
Duration:               280             280
Duration@.050        260             260
Lobe Center           103             103

Intake opens 27 Befor TDC Exhaust Opens 53 Before BDC
Intake closes 53 After BDC Exhaust Closes 27 After TDC

Valve timing is checked with zero valve lash @.050 inches of valve lift

Thats what the card says

I'm at 21 degrees BTDC at .050, duration of 233 with a Lobe center of 116.5.

[scondon]

When I timed my Webcam the open/close #'s did not match the provided timing card, a common problem. These cams have a "square" profile, look at the #'s and you'll see what I mean (intake: 27/53, exhaust: 53/27). When finding initial sweet spot, just make sure you have "mirror" #'s on intake/exhaust,  ex: 24/57 - 57/24

Just to say, if you set intake open to 27 BTDC and then find that intake close is way off, don't be surprised. I set mine to square and then measured at different inches of valve lift. I think mine matched the card at .038 lift. Hope this helps 

[KB02]

Well, I've got timing set at 26 degrees BTDC on the intake @ .050. The engine turns no problem now.

I might have to diddle with it a bit more to get it sqaure. Or I might just go with it as is. Or I might just leave it and run it the way it is. We'll see.

[scondon]

Well, I've got timing set at 26 degrees BTDC on the intake @ .050. The engine turns no problem now.

I might have to diddle with it a bit more to get it sqaure. Or I might just go with it as is. Or I might just leave it and run it the way it is. We'll see.

What is your intake close # ?

[KB02]

31

[MRieck]

 I'd be more concerned with the exhaust valve as that is the one closing as the piston is ascending. If it is closing real late you will smack it. I'd also measure piston to valve clearance 10 degrees before and after TDC

[scondon]

Well, I've got timing set at 26 degrees BTDC on the intake @ .050. The engine turns no problem now.

I might have to diddle with it a bit more to get it sqaure. Or I might just go with it as is. Or I might just leave it and run it the way it is. We'll see.

What is your intake close # ?

31

That's a 22 degree difference from the timing card. I would suspect that the cam is 11 degrees out of position. Webcam timing cards can't be used as is. There's just no skipping measuring both intake and exhaust to make sure cam is "square." If you want to advance or retard a few degrees you can do it at this point.

[KB02]

Alright. I will back it down from 26 to 15 and remeasure everything. I will report back with the new measurements. Might be tonight, but most likely not until the weekend.

[KB02]

Okay, to the best of my timing ability, the Cam is square.

Here are my measurements taken with 0 lash and at 0.050 lift:
Intake opens at 17 degrees BTDC
Intake closes at 40 degrees ABDC
Exhaust opens at 40 degrees BBDC
Exhaust closes at 17 degrees ATDC
Overlap: 34.00 degrees
Intake Duration at 0.050: 237.00 degrees
Exhaust Duration at 0.050: 237.00 degrees
Intake Installed Centerline of 101.50 degrees ATDC.
Exhaust Installed Centerline of 101.50 degrees BTDC.

The top section are my measurements. The bottom section was calculated using the tool on Webcam's website. Duration is certainly off from what Webcam boasts of 280. I'll double check the lift tomorrow before I button the top end up, but I don't think it's quite 360. Then again, they don't, technically, list the duration at .050, they just list a duration.

http://www.webcamshafts.com/index_blank.html?pages/vehicle_search.html
Motorcycle - Honda - CB750 SOHC 8v - 41a

[MRieck]

Okay, to the best of my timing ability, the Cam is square.

Here are my measurements taken with 0 lash and at 0.050 lift:
Intake opens at 17 degrees BTDC
Intake closes at 40 degrees ABDC
Exhaust opens at 40 degrees BBDC
Exhaust closes at 17 degrees ATDC
Overlap: 34.00 degrees
Intake Duration at 0.050: 237.00 degrees
Exhaust Duration at 0.050: 237.00 degrees
Intake Installed Centerline of 101.50 degrees ATDC.
Exhaust Installed Centerline of 101.50 degrees BTDC.

The top section are my measurements. The bottom section was calculated using the tool on Webcam's website. Duration is certainly off from what Webcam boasts of 280. I'll double check the lift tomorrow before I button the top end up, but I don't think it's quite 360. Then again, they don't, technically, list the duration at .050, they just list a duration.

http://www.webcamshafts.com/index_blank.html?pages/vehicle_search.html
Motorcycle - Honda - CB750 SOHC 8v - 41a

Those LC #'s look good.

[KB02]

.330 lift with 0 lash. not quite 360, but that's what I measured anyway.

[MRieck]

.330 lift with 0 lash. not quite 360, but that's what I measured anyway.

Oh I know what you mean...........