What is the drag/resistance I encountered when hand cranking engine during valve adj?

[Guest]

Hi all,


I was doing a valve adj on my 81 550t and while hand cranking the engine (clockwise) I encountered various points on the rotation that had substantial drag and resistance. nothing that felt like a seized engine, but fairly noticeable. On other points, the engine would swiftly turn as if pressure was being released and let out a loud breath of air. I have since adjusted all clearances within spec, put in a new gasket and put the valve cover back on. I have not checked my cam timing yet, which according to the pdf manual for my bike on bikecliff's site seems to be 20 pins beginning with pin directly above arrow 2 (counted as #1) and ending directly above arrow 3.

I am waiting for a new petcock to get shipped in order to address starting issues, so figured I'd post here while I wait...

Any ideas? the valve adjustment was my first experience getting into the engine. 5 clearances were out of spec (4 had zero clearance and 1 was too loose), so who knows how long the bike ran like this. Just hoping whatever needs to be checked/done will be doable for me.

thanks

EDIT*
remembered something that may be useful - when using the zip tie method to shim the valves during the adjustments, I did sometimes notice what seemed to be disproportionate carbon buildup (either a lot or almost none) on the edges of the valve that were visible from the spark plug holes.

 

[posplayr]

It is called compression?

Pull you plugs and see if it goes away.

Also even with the plugs out you will see differences in drag as you turn the crank. When a piston is near TDC, it barely moves compared to the crank rotation. So there is very little ring/piston to sidewall resistance at this time. When the piston is near mid stroke, resistance is MAX .

 

[Rich82GS750TZ]

Maybe I’m missing something, and please, no offense intended, but why wouldn’t you at least look at the cam timing while the valve cover was off? I mean, they were right there in front of you. All you had to do is look at it while you were cranking the engine.

 

[Guest]

gotcha, thank you! all plugs were already pulled when I noticed the resistance, I figured it was probably something moreso to do with my lack of engine knowledge, but was recommended in a different thread to pose the question here bc it wasn't a good sign so wanted to do so just in case.

 

[Guest]

Maybe I’m missing something, and please, no offense intended, but why wouldn’t you at least look at the cam timing while the valve cover was off? I mean, they were right there in front of you. All you had to do is look at it while you were cranking the engine.

haha very good question and no offense taken! This is my first vintage rebuild project so to be honest I didn't even think to check when I had the valve cover off. my mistake. Doing it all for the first time, things definitely don't happen in the the most efficient manner..

I'm going to check cam timing tomorrow and then will report back.

 

[Rich82GS750TZ]

I was where you where you are now about a year and a half ago, taking the valve cover off for the first time to check clearance. That job is daunting enough, without thinking about anything else. I totally get it. You’re doing great. You got the manual. And your doing things by the book.

 

[2BRacing]

........ while hand cranking the engine (clockwise) I encountered various points on the rotation that had substantial drag and resistance. nothing that felt like a seized engine, but fairly noticeable. On other points, the engine would swiftly turn as if pressure was being released and let out a loud breath of air. .....

The various stages of "drag/resistance" and then "swift/free" motion are perfectly normal. It is caused by the various cam lobes starting to depress a valve against the spring ("drag/resistance"), and then when the cam turns past the lobe, the spring forces the valve up and the crank suddenly seems to turn "swiftly/free" as the cam position is on the heel (opposite end to lobe).

If the cam timing was so far out that one or more valves could hit the piston/s, you would not be able to turn the engine any further clockwise at all by hand. However, it will be good experience for you to check that it is correct by following the procedure in the manual. Set the crank at TDC #1, with the notches in the cams pointing inwards towards each other as shown in the manual, and then check the alignment of arrow #1 and count the number of pins between arrows # 2 and #3 as per the manual.

 

[bwringer]

Nice explanation, 2B.

If the plugs are out, then you'll feel alternating resistance and "pushes" from the valve springs at various points. Perfectly completely 100% normal.

I usually don't bother to remove the plugs during valve checks (the less wear on aluminum threads, the better), so I also feel compression and hear air slowly wheezing past the rings.

Also, if the transmission isn't in neutral, then you'll also feel a little added resistance, probably hear some clunks as you take up the running clearances in the gearbox and drivetrain, and oh yeah, the rear wheel will slowly turn. Completely not an issue, as long as you remember to put it back in neutral before you fire it up.



Tangential anecdote: I was once doing a valve check on a Suzuki TL1000, and on that engine (and many other modern-ish Suzukis) you are supposed to remove a plug in the crankcase and reach in with a socket to turn the crank. As often happens, the stupid plug was stuck fast, and could not be removed without destroying the plug. Rather than order up another plug and come back to it a few weeks later, I put the transmission in gear and had the owner slowly turn the rear wheel until the crank was in the correct positions.