B230F - timing, compression related

[e777]

If the timing marks on the harmonic balancer and the camshaft sprocket are lined up properly, does this necessarily mean that the engine is TDC on the compression stroke, or could it be the expulsion (or whatever the exhaust cycle is called) stroke? How does one know whether the stroke is compression or expulsion?

Thanks!
86 740 236K

[jimmy57]

The camshaft mark being lined up will mean it is on the compression stroke. The camshaft is coordinating valve opening and closing and that is what controls whether the piston is compressing on its upward travel or expelling exhaust on the way up.
The mark on outer balancer diameter may not mean it is EXACTLY in the right place for assembly. The balancers are know to slip as the outer metal portion is connected to the inner portion attached to crankshaft via rubber sleeve. The bond between the rubber and the metal can fail. The last bit of info may not be relevant to what you are trying to discover but I included it in case you are removing and refitting timing belt.
What are you checking?

[e777]

Thanks very much for the info.

What happened is this: I just did a compression test and all four cylinders produced uniformly low compression: 95 psi. While I was discouraged at the low compression, I saw hope when I realized that there was no disparity between the cylinders' compression. After some research, I saw that there was a great possibility that the camshaft might be off a bit, thus leaving the valves slightly open during compression. I did change the timing belt recently, so I might need to check the camshaft timing marks again. I hope that is the problem!

Then again, the (rental) compression meter might be off, so that is the first thing I'll test before anything else.

Thanks again.

[jimmy57]

IF you didn't hold throttle open while cranking engine for the compression readings, then repeat test.
You can open throttle via linkage under hood and wedge or wire the throttle spool in the open position. Does not have to be wide open but at least half way to assure enough air into cylinders to compress for valid readings.

[e777]

Thanks. I did have my "assistant" (wife) hold the throttle open while I cranked the engine.

[Retired MVS Contributor]

The timing mark on the harmonic balancer is NOT for installing the timing belt, it is for ignition timing ONLY...The timing mark for timing the belt is on the crankshaft sprocket and when it is properly lined up the sprocket mark will line up with the line on the crankcase slightly to the left of center...If you used the ignition timing mark on the lower timing belt cover, you are out of time and that would account for a lot of your problems...I can not imagine how you might have used the ignition mark on the cover, the cover has to be removed to get the belt on and off and is entirely out of the picture when belt timing is being set up...Use the mark on the crankshaft sprocket...

Jerry

[e777]

Thanks, Jerry. What you say makes sense. I did replace the T-belt referencing the camshaft mark, as the crankshaft mark isn't even in the picture.

[e777]

Please forgive my ignorance, but I have one last question before re-checking my T-belt: If the T-belt's function is to synch the crank and camshafts, and the only mark used for setting the engine at TDC is the camshaft mark, then how can we be sure the crankshaft is in synch with it? For example, if a T-belt breaks while driving, then how can one be sure the crankshaft is re-set properly in relation to the camshaft?

[jimmy57]

There is a crank gear referenced marking used when the damper pulley is removed for access. You move the crank to the point where the crank gear mark is aligned and you turn the cam gear until its marks are aligned. If you have a distributor in the engine block you must put the intermediate gear in the position where its mark is aligned with the indicator also. Then you place belt around the gears being sure no gears move during that step.

[e777]

Great. Thanks very much for the info.