Timing Gt750 problems

[smokin]

I rebuilt the engine (72 GT750) bored 1 over and crank done by bill bune, using suzuki service manual, dial gauge and ohm meter, I've set the points gap at .014 and the timing plate at he timing mark for each cyl at TDC, the timing plate is way off compared to the dial gauge, at TDC on the dial gauge the timing plate is past the mark by about 10mm, the points I can not adjust correctly the gap is to wide so inorder to get the points to fire I have to reduce the gap to around .02-.03 then I can get the timing to suzuki spec, adjusting the points plate doesn't help, the timing plate and cam are in the correct position and I started with the left cyl first, havn't tried to start it yet that will happen later just trying to time it for now, what can I be doing wrong did every thing the manual said but all the adjustments are out of wack.

Smokin

[Coyote]

You don't set the points at top dead center. You set them at a specified amount before TDC (BTDC). I your case the left and right cylinders are set at 3.64mm BTDC and the center is set at 3.42mm BTDC. In thousanths that's .144 left and right. The center is .135. Always turn in the direction of rotation.

[smokin]

Coyote when I set the left and right points at 3.64mm and the center at 3.42mm the gap between the points is (.002), if I gap the points first (.014) before I time it I can't get it to time right because the points open to soon and you can't adjust it by moving the points plate so I have to reduce the gap in order to get it timed right, with the gap being at .002 the points will probably end up burning up. I am not trying to set the points at TDC just letting you that the timing mark on the timing plate are way off from what the dial gauge reads, I'm thing that the cam could be off if the timing plate is off I checked the plate and cam and they are in the right spot, is this normal for the gt or am I missing somthing.

Smokin

[Barry S.]

What brand of points do you have, some have shorter rub blocks that are hard to time because you run out of adjustment. The gap must be set first at .014" and the marks don't line up at max gap but when the points first break open. I checked mine once with a dial gage and the timing marks were right so ever since I've used only a timing light.

[tz375]

It's probably a communication issue but it's not clear to me what you are doing or seeing.

Set the points at or just after TDC when they are fully opened by the points cam. Then rotate the motor forwards to say 4mm BTDC and watch for the instant at which the points crack open. Use an analogue meter or buzzer. That should happen at the timing marks and at the correct distance BTDC. Those timing marks are often many degrees out of place. The timing wheel is held in place by the pin that locates the points cam but are a sloppy fit.

It is possible that your motor was assembled without that pin and that the timing disk and cam are held in place by friction and the clamping force of the nut on the points shaft. The points shaft is keyed to the starter clutch with an 8mm hardened steel pin which engages in a slot in the back of the points cam.

Does the starter work ok? If not, maybe the woodruf key locating the starter clutch to the crankshaft has sheared off.

if teh motor doesn't run at all, check that all three coils are wired to the correct sets of points.

[Buffalo-guy]

One other thing. Adjust the timing on the left cylinder first. Those points are adjusted by turning the points plate. The center and right are adjusted individually after the fact. If the points are the correct ones, this should work. Cheers.
Fred

[TLRam1]

Then rotate the motor forwards to say 4mm BTDC and watch for the instant at which the points crack open.

Looking at the motor from the left side, normal rotation is counter clockwise, correct? Than you rotate the motor clockwise to the 3.4 or 3.6mm mark where the points should crack open.

Is this correct or am I missing something.

[smokin]

Thanks for the help, I think I figured out the timing plate problem, the timing plate behind the points plate is set up to read at BTDC is this correct? on 4 strokes it's usually TDC this is what has me confused.
This is how I set the timing and points, left point first, gap point at .014, set dial gauge TDC small needle a "4" large needle at 0, rotate crank counterclockwise all the way around until dial reads 3.64mm, set points to start to open. Here is the problem the left points are already wide open moving the points plate doesn't close the points to were they will just start to open, I have to close the gap on the points inorder to get them to were they are starting to open instead of .014 the gap is .002 now they are barely opening.
The right and center are the same way I can only adjust them so much before I have to close the gap, the gap on these aren't as bad (.005-.008) as the left side, I don't know what brand the points are but I changed them with an old set that I had and they were the same, do you think this is a rub block problem with the points or am I doing something wrong?

[tz375]

Terry. That's correct.

Smokin, yes the timing wheel has marks at F and not at T.

This stuff can be confusing, so let's try that again.

First set the points gap on all 3 as follows:
Turn the motor until the left points are as far open as they will go. I previously said that should be about TDC or just after, but what's important is they must be wide open. Adjust the gap to 14 thou. Rotate the motor and recheck to be sure that they are open 0.014" when they are fully open.

Just for interest sake note where the points reach full open.

Repeat for Center and Right points.

Now let's set the timing.
Get motor to TDC on the left, with dial gauge reading ZERO.
Rotate teh motor one full revolution and be sure that the gauge still reads zero at TDC (do it slowly)

Rotate forwards past BDC and as it starts to come back up, watch carefully once it gets to about 4mm because that's just before the points should open. Watch for where the points start to open and adjust the backing plate until they open at 3.64mm.

Repeat for C and R but this time the individual points can be adjusted for timing.

Try that and let us know what happens.

[smokin]

Ok tz375 I did what you said but the points on the left cyl open way to early, they start to open around 1.34mm by the time I get to 3.64mm the points are almost wide open can't adjust with the points plate. I can set the points to start opening using the ignition plate behind the points plate, if I line up the ignition marks then I can adjust the points from there will that work?
I was talkin to Ian and he thinks the rub block are worn down so I'm going to order some point an see if that works, can I set the points by using the ignition plate that looks alot easier or will I have problems with timing later.

Smokin

[rngdng]

I purchased some new aftermarket points once that had the wrong size contact block, and nothing I could do would make them work. Beware of imitations......



Lane

[tz375]

Smokin,

Something wrong here. As I understood that last post, the points start to open at 1.34mm and by 3.6 they are fully open. If you rotate the motor forwards and are timing it BEFORE TDC then they would open at say 3 or 4mm and get wider as you approach TDC ie the reading gets smaller as it gets closer to TDC. At TDC it reads zero.

If yours starts to open at a small number and gets wider as the gauge reads higher, it's going backwards or it's AFTER TDC.

It's easier to show this stuff than to describe it - what's that saying about pictures and 1000 words.

See http://pinkpossum.com/GT750/images/PB130009.JPG" onclick="window.open(this.href);return false;

In that one I had the head off but the principle is the same. As the piston rises towards TDC the reading on the DTI gets smaller. After TDC the reading gets larger until it reaches a max of 64mm at BDC (if you had a long enough DTI).

Does that make sense? PM me your phone # and I'll call and talk you through it.

[smokin]

Thanks Rich, he really helped me out with that timing problem, I guess it depends on what type of dial gauge you have I have a suzuki dial gauge and what the manual tell you what to do doesn't work, I had to do everything kind of backwards I can't explain how we did this it's kind of confussing anyway thanks Rich.

Smokin

[smokin gt750]

Hello, I attempted to set the timing on my GT750 by the Cylmer manual. I also attempted to use this forum and others. I finally figured it out. The manual states turn the engine counterclockwise. I believe this is not for a 750 since the timing plate is on the left side, you should turn the engine clock wise and it worked like a charm the first time. Go figure!

[rbond]

If the points are on the left side of the engine, then the crank is turning counter-clockwise. If on the right side, then clockwise. Offhand I only know of one (Japanese)engine that actually backwards.(Kawasaki 750 twin)