Hi, I've just rebuilt a 1977 GT380 and I'm worried over the timing. I've set the timing using the propeller seen through the points backplate. I turned the engine over using the kickstarter until the mark for the left cylinder lined up with the mark on the casing. I then rotated the points backplate until the points began to open using a home made light bulb indicator, ( the light came on just as the points began to open ). I then tightened up the backplate. I repeated the process for centre & right cylinders adjusting the movable points plate. All great so far until I purchased a workshop manual and it states this method should only be used in emergencies as damage can occur. I've holed a few pistons in my time on other 2 strokes so can anyone please tell me a sure fire way of timing the engine correctly.
I've just ordered a dial gauge, but I'm not sure of the BTDC setting, and should the points be just opening as I set them before. The Haynes manual is not very clear.
Is there anyone who can give me a step by step rundown on the timing procedure.
Oh by the way the engine seems to run fine using my first method but I've been told not to run the bike as it's not accurate enough.
You're good to go. You have timed it using the correct method. The timing mark on the casing can be anywhere from close to spot on. I never heard of it being dangerous to run it just the way you have it now. You can double check with a dial gauge if you want, but I have found over the years that it's really not necessary. The distance BTDC is specified in the sticky 'General specs and info' found at the top of this section. I have timed with a dial gauge and the bike ran fair. Then used a strobe only to find it to be a few degrees off from the provided marks on the case. Adjusted it in to the marks using a strobe and the bike ran (and still runs) great.
So if your bike is running good timed with the provided marks, it's time to ride it and enjoy it. No worries! Never heard of running that way being a bad thing. What you can do if you have a dial gauge is time a cylinder using the gauge, then look at the timing propeller and see how close it is to the mark. You will be surprised how close that really is. The owner and head mechanic at the bike shop I frequent has been timing all sorts of bikes for 35 years. He always times to the marks if they are provided. Then if it runs good, that's where it stays. With these sloppy old 2 strokes you have to be off a country mile to ever hole a piston due to timing. Super lean condition holes pistons. Timing rarely plays a role. RIDE IT!
I was born with nothing and still have most of it left.
+1 what Coyote says. You don't say if you've gapped the points first though, they should be 14 thou +/- 1 thou when on the top of the points cam. Then set the timing, just opening as the marks align. The actual timing varies with the model of GT380, finishing about 2.1mm BTDC on the A and B model.
Cheers,
Mike
I would not depend on static timing. Buy a dial gauge to set the timing. I never resorted to using one because I was a little intimidated never having done so. But, it's a piece of cake. If you set it by static timing. The bike runs well and makes good power up steep hills, great. But, I found out the hard way on my 750 that static timing doesn't always work out. I timed that bike correctly a thousand times during a long drawn out time period. Each time it would start, idle, and run smoothly for a few miles if I didn't approach any steep hills. I replaced every electrical item on the bike, even though those parts were brand new thinking something else was causing the problem. After trying everything possible to correct the problem. I finally resorted to purchasing a dial gauge. The bike was golden after the first attempt. Something to remember if you have problems.
OH MY ! More conflicting info. I now have a dial gauge but need the exact BTDC for a 1977 GT380 B. I have a manual which only covers models up to 1975, which states 3mm BTDC. I'm sure this is incorrect for my model. .
For the A/B models it's 2.1mm BTDC for the outer cylinders and 2.05mm BTDC for the centre cylinder (the difference is simply because the spark plug holes are at different angles, the actual firing point is the same for all 3 cylinders).
The one thing I would suggest is this (and this is purely my 10 pence worth): don't turn the backplate to get the points to open when the marks line up; instead, nudge the engine in tiny increments using the kickstarter until the timing light shows the points are just opening, and THEN check the timing marks.
If an adjustment needs to be made, make it, then check again using the method above. I've found that tightening the backplate screws can move the timing slightly, so I prefer to check the timing when all the screws are buttoned up snug, and recheck with everything buttoned up after making adjustments.
But as stated above, usually the marks on the propeller are close enough - although it's good to check how close they are using a dial gauge if you have access to one.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
Let's put all those replies into perspective. In some cases, the propeller is so close that it doesn't much matter, but there is quite a lot of slop in some of them and they can be far enough out to make a difference.
If the bike runs fine, then it's probably OK and I wouldn't lose any sleep over it but it would be a good idea when teh time is right, to get a dial gauge and set the timing accurately and ten see where the propeller lines align. If they are pretty damn close, then just use them in future.
ALWAYS double check and triple check, as Craig stated, things do move when you tighten them home. How much things move varies. If it always moves the same amount, you can compensate that amount on the indicator so that it puts it in the right place when you tighten up the screws. I have played that game for hours. Came away successful, with a sore back.
I was born with nothing and still have most of it left.
Oh Dear, Something must be wrong somewhere. I've set the BTDC to 2.1mm on the left cylinder using a Dial gauge and checked the position of the L mark on the propeller as suggested. It's a country mile off, at least 20 degrees past the mark on the casing. The L mark on the propeller actually lines up when the piston is at 4.5mm BTDC. Hence there is not enough adjustment on the backplate slots to set the points to just opening at 2.1mm BTDC.
Could I have put the clutch casing back on wrong ? I lined up the centre punch mark on the small gear with the pointer plate, then lined up the L mark with the rib on the casing and slipped the casing back on. All seemed well.
Do you think I should buy another gasket and have another go at lining everything up. How come the bike runs well if it's so far out, I'm at a loss.
Are they new " factory " points sets as some after market points can have too short rubbing blocks and if they are factory but not new it can also be the problem the rubbing block that rides on the cam has worn down too short , Lube should always be used on the felt to help avoid rapid wear on the points rubbing blocks .
Getting the points gap right is a big determinant of where the paddle will be vs the static mark when the points open. Personally I set the timing a tad (small fraction of a mm) advanced and with points at 15 thou so that over a few thousand miles the timing will slowly retard and the points gap close up, as the points heel wears. If your points gap is on the small end of the range, you'll be moving the backplate (and points) further round before they open. Before I understood this (back in 1979) I even took my points plate off and filed the slots in it so as to allow the plate to rotate further! its still like that today, though now I'm bang in the middle of the factory slot
Mike
As Dave and Mike said, start off by checking the points gaps when they are wide open and then take another look to see when the points start to crack open on the DTI and on the propeller. 4.5mm is so far off that it suggests either an error in measurement technique or a timing gear one tooth out.
I'd do the second and third check of points gap and timing first and if necessary, post some pics of what you see as the points start to open. I don't know if this would help but if you set the motor at TDC on one cylinder and take a picture maybe a 380 owner could look at that and see anything obviously out of place.
Sounds to me like the nylon gear is 1 tooth out. You said it was running fine. Was that before or after messing with the clutch cover? Something is way out. Increasing the point gap may help, but it's not going to take care of 20+ degrees out.
I was born with nothing and still have most of it left.
When replacing the clutch cover on my own 380, I line everything up nicely and then have to ease the cover on REALLY carefully, because even with all the marks lined up, the nylon driven gear does not mesh neatly with the drive gear, it needs to be eased on.
It would be easy to slip a tooth ... I ended up putting the cover on a couple or three times before I was satisfied in my own mind that it was right.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
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