Need clarification on GS450 timing TDC piston location

[sacruickshank]

While doing a tear down on an '83 GS450 for multiple reasons, I've noticed that the TDC markings (R - T||F) on the timing plate don't seem to correlate to the RH piston being at TDC. This doesn't seem right, is it?

The timing chain has been off, but I don't see how this could affect the piston location since the crankshaft (not the timing chain) drives the piston location.

I've had this bike for a few months, so don't know what PO did to it. It was running before I brought it home and a 5 mile test ride went fine, except for some air leakage engine revving.

Here's a pic of the timing plate. Couldn't upload piston image for some reason.

Any ideas?

[sacruickshank]

Pic of piston

here's a pic of the piston. Apparently a reply allowed me to attach the piston image

[sacruickshank]

From reading the clymer manual, the indicator on the engine case is the notch near the left most screw in the image. The markings on the 19mm crank turner nut are supposed to be those marked R T||F, unless I'm misreading something in the manual.

[OldTwin]

This is how it looks on my '81, and RH piston is definitely at TDC. Something definitely does not appear right on your motor, is the alignment pin on the crank intact?

WIN_20170124_09_30_09_Pro.jpg

[OldTwin]

This is the pin I'm referring to...

WIN_20170124_09_51_07_Pro.jpg

[sacruickshank]

The crankshaft timing pin is still intact, but looking at your pics it seems they changed the design between '81 and '83 450's. My bike ('83) has the markings on the brass sleeve that fits over the pin, as shown in my first image. Yours has the markings on the part which has springs and sits under the points plate, while mine has no such part.

'83 BikeBandit link http://www.bikebandit.com/oem-parts/...1341#sch234138
'81 Bike Bandit link http://www.bikebandit.com/oem-parts/...1417#sch264952

My image doesn't include the plate that has the points, but that plate does not have any TDC or related markings. I'll re-check when I get home and post another pic if needed.

[OldTwin]

Curious that there's no mechanical advance on your motor and the plate with markings does not laterally align with the index mark in the casting. Seems like the PO made some questionable mods...

Nope, checked the signal generator illustrated parts schematic and yours looks correct. Perplexing.

[sacruickshank]

True, but would you trust the physical observation enough over the words in the clymer manual to set the timing for the valves and cams?

If I set the RH piston to TDC and position the camshafts per the manual, the LH exhaust lobe is perpendicular to the valve, i.e. fully opened. This could make sense since the LH piston is at the bottom of it's run when the RH piston is TDC. But then I have to make sure I'm in the correct portion of the firing cycle so that the intake valves are letting fuel in before the spark plug fires. Back to the basement tonight.

[OldTwin]

Yes, RH piston at TDC and valves properly timed as described would be of primary importance as Nessism indicated, timing marks on rotor would be of secondary importance. As Nessism asked, where are the timing marks when RH piston is at TDC on combustion stroke? Can you post a picture in that condition?

[sacruickshank]

IMG_20170124_181921505.jpg

Here are pics (next one to follow) with RH piston at TDC and the corresponding timing marks. Assembled it once with this situation and cam shafts at appropriate position per clymer, and still had the intake valves on both sides opening right when each piston was at TDC. Seems like the intake cam shaft is 180 deg too soon, but I'm doing everything else by the book, such as 18 timing chain pins between the 2 arrow on exhaust cam shaft and the 3 arrow on intake cam shaft.

[sacruickshank]

timing marks

IMG_20170124_182140378.jpg

[OldTwin]

You're actually 360 degrees out of cycle starting the intake stroke rather than the combustion stroke.

[sacruickshank]

Thanks all. The current positioning is allowing all pistons and valves to move as intended, but it's hard to say if it is the proper position relative to the intake or combustion stroke.

The challenge with having LH piston at TDC is, if I follow the rest of the clymer instructions wr.t. initial position of the cam shafts, then the LH exhaust valve is fully open (or almost fully open) when the LH piston is TDC causing an interference problem.

I'll look for a better resource than the clymer manual, which is vague in this topic since it's trying to cover three different 400 models (400, 425, 450) from a broad range of years. Also, the image for the 450 reference is poor quality

[sacruickshank]

Thanks for the straight forward explanation.

I believe the signal generator is correct based on Bike Bandit/fiche links, and that the previously mentioned piston/valve interference is due to the subtle diffs in positioning the exhaust cam and timing chain tightness. I'll re-try tonight.

[John Park]

Whether the LH or RH piston is #1 is a good question. But the timing is RH piston TDC and the EX cam arrow forward and the correct pin count to the IN mark.

You can't be 360 degrees out because the only thing that would matter to is the camshafts and you haven't put them in yet. The ignition runs off the crank and fires every 360 so it doesn't care.

In auto engines the #1 cylinder is at the opposite end to the output/flywheel, by convention, but on these engines the flywheel is opposite the output. So here we're timing to the #2, I guess. With only two cylinders, R and L is all you need to know.

In a related topic, I recently took apart an advance plate and got the rotor on 180 degrees out. Interesting exhaust note when the thing fires at the bottom of the stroke with the exhaust valve still open.