Crankshaft seal question

[Eddie]

Hi, I just had a question about crank seals, is there such a thing as a seal that is going bad but not totally bad? I heard that if seals are bad they are bad and there is no in-between ? Which is true?, my left cyl. On the gt750 smokes a little more than the others and when I check the plugs the left one has a clear oil or fuel not sure , ring around the top but the porcelain is looking ok, slightly lean, then when I check the others they have a black sooty look around the top and center looks ok, it's like the left cyl. Is either not firing right or maybe seal going? I'm at work but when I get home I'll take a pic. I put the stock pilots back in and I went up one size on the mains and the clip is one notch from the top, because in the middle it was to rich, so it looks like I can stay with one size bigger on mains and have clip almost at top, or go to stock mains and have the clips one notch from the bottom!

[oldjapanesebikes]

Seals can and do degrade - typically crankshaft seal failure is progressive rather than like someone flipped a switch. For your other questions, it sounds more like timing and carb related issues - if you are running points, how are you setting them ?

[Eddie]

I am running the newtronics kit no points , so mayBe it's the timing ? The carbs seem to be ok but then again they are bs40 and it seems like they are very fussy compared to my other bikes...

[oldjapanesebikes]

If you haven't done so already, use a strobe light to set your timing. You should also check to see what sort of voltage drops you are getting in your wire harness.

I'm not an expert by any means, but I would not have said the BS40's were any worse than any other type of 30 to 40 year old carburettor. Parts wear, air leaks happen, tiny passageways plug up - so if they are clean, mechanically sound and set up properly with a stock airbox/filter and with inlet/outlet manifolds that are in good shape then they work just fine.

[Eddie]

I agree, any old carb has problems and they all need attention, but it just seems like my fuel curve is all over, one minute it's rich , then lean, it's just a little aggrevating , I am used to working on keihin carbs, then again the keihins I usually work on are 60's era these bs40 s are a lot more advanced I guess then the early 60's keihins. I think the problem may not be the bs40 carbs but possibly my low compression on a couple of cylinders, I think I need a fresh bore and new pistons and rings, I think the rings might be seized , from sitting for all these years, I could see some scaring on two of the cylinders, I actually like the carbs, just getting frustrated with them....

[Eddie]

Also , I set the timing with the dial gauge , you think I should use the strobe instead? This was my first attempt with the dial, and if you put a strobe on it , the marks are pretty far off when you compare them. The timing is more retarded with the dial, I think, I'll have to recheck but I know the dial and strobe were both different and I stuck with the dial, so maybe try the strobe? I love the bike, just trying to not rebuild it right now, I would like to get some more riding out of her ,

[oldjapanesebikes]

For normally tuned engines, and assuming there isn't something wildly wrong with the crank or the timing arm and marks, the strobe will give you a better result than will a dial gauge on an electronic ignition. With points, you can use the gauge and a powered light bulb across the points to see just when they open and be just as accurate if you are skilful, although I tend to still use the strobe for the final set. If I recall correctly, with the Newtronic set up you can dial in each cylinder's timing individually, so you would strobe all three and adjust as required.

If it were my engine, I'd set it using the strobe and see how it runs - the fact you say it is showing as being currently retarded compared to the strobe indication may be your problem. Others may chime in with their own opinions.

[tz375]

I agree in principle with Ian, but my experience is the opposite. There is so much slop between the three legged propeller blade used for timing and the pin it sits on that timing can be a long way out.

I always use a dial gauge to check and/or correct the timing wheel first and if it's spot on, strobe it. Even then I tend to use a 6" or larger timing disk and pointer and find TDC first.

[Eddie]

Well it's been a while since I did it, but I had the timing plate , or three legged timing propellar on it, I then checked top dead with the dial, and the marks on the timing plate were like a quarter of and inch off from where the dial said top dead was, I used the timing degrees from the book, I brought the piston all the way up, then I backed it down to where the book said it should be, I don't remember what it was right now but I know one was like 42 degrees b.t.d.c., anyway when I got the piston where it should be according to the book, the marks on the plate were off, I had to retard one cylinder so much I had to make the slot in the plate longer just to get it right. I double checked it because this did not seem right to me but that's what I kept getting so I went by the dial, maybe I will put the light on it but I know it will be way different with the light so I'm not sure what to do, the newtronics kit even said if the marks on the plate were off just scribe new marks on the original plate? So I just marked it with a sharpy for now....so what you guys think?

[tz375]

Measure TDC carefully first and then rotate engine backwards and bring it back up to the correct dial gauge reading. If the propeller mark is wrong, mark it with a Sharpie. After that you can use the marks and a strobe.

Just as a double check, you can get a large diameter timing disk like this one from AF1 - http://www.af1racing.com/store/scripts/ ... oduct=1132" onclick="window.open(this.href);return false;

The larger the better. Bolt it to the alternator and make up a pointer from stiff wire or a wire coat hanger and check to see that your mm reading on the dial gauge corresponds to the appropriate degrees listed in the Shop Manual. If the dial reading is very different to what the manual says, it may be the way that the dial gauge is set of the way it's being read.

If that's all good, use it to mark the propeller and you will know it's spot on.

[oldjapanesebikes]

....so what you guys think?

It would seem I've been quite lucky as I have never seen an instance of a large discrepancy between the factory marks/propeller and what they when measured using a gauge/dial. Spot on ? No. But they have always all been close enough as really made no noticeable difference in either fuel economy or performance for average road use, so I'm not sure what to think .................

[Eddie]

Thanks for the help! I use to have a degree wheel but not sure what happened to it, I will check it again with the strobe, just to see where it is now, then I will recheck it with the dial when I get time, I have been working a lot , plus keeping the wife happy is a full time job, plus kids, no time for anything lately!

[T350guy]

Eddie
I have an Accent iggy on my Gt 750. I used the dial gauge on the center cylinder to set the Timing.
The Accent has a light that goes on when the propeller triggers it.
I set the timing to 3.42mm BTDC and like you my center mark does not line up and is actually retarded if you look at the marks.
If I lined up the marks then check my gauge it is now too advanced , I think it was around. 3.6 or 3.7...doesn't hurt it as I ran it this way with points set to the marks ( No gauge )
I used a timing light after and the new mark lines up as set to 3.42