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Post by marsbar350 on Sept 4, 2016 21:47:08 GMT 1
need for peace of mind to check my crank  how is it done? TIA  |
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Post by 4l04ever on Sept 4, 2016 22:12:38 GMT 1
Put a mark on the flywheel from a known reference point (timing line?) for left cylinder Top Dead Centre and one for right cylinder TDC. Measure around the outside of the flywheel from one mark to the other both ways and the measurements should be the same within a millimetre. If it is longer one way and shorter the other then the crank is twisted.
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Post by steven on Sept 5, 2016 0:00:04 GMT 1
With two clock gauges.
When one piston is TDC the other one should be at BDC.
I have photos somewhere I will dig them out.
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Post by bare on Sept 5, 2016 2:38:05 GMT 1
Tricky that; BDC should be OK.. maybe.. but TDC will run into "dwell" issues, as TDC isn't a fixed / exact measurement point in the crank's rotation... it's a segment of it's arc.
Which can easily hide small twistings.
A single silly mm is decidedly 'out' IMO... But wayy better than 6mm
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Post by steven on Sept 5, 2016 8:54:29 GMT 1
... Knew I had the pics somewhere, here is the set up I used, Im always paranoid the crank twists when I tourque up the alternator/ignition rotor, so I made this afair up to check mine with two clock gauges. I cut up some spark plugs, and machined them out to accept some silver steel bar that is a nice sliding fit. Bare, I hear what you are saying about a dwell at TDC, but if there is a dwell at TDC there will also be one at BDC, wont there ? In practice, it is minimul and TDC/BDC can be acurately found using two clock gauges. If this method of finding TDC is not acurate, how are you going to acurately set your ignition timing ? With the engine assembled, is there an any more acurate way to find TDC than the above method ? Using a timming pointer like the ones I made up, is the approved method for finding TDC and setting your static ignition timing, which then allows you to set the ignition/alternator backplate with the fixed index mark, which is then used to check your dynamic ignition timing with a strobe. Yamaha even list a set up scimilar to my home made afair for finding TDC, it mentions the Yamaha part numbers of the gauge and pointer etc in the Haynes manual, but we all knew that anyway. Im off to bed now, I hate night shift ! steven.      |
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Post by 4l04ever on Sept 5, 2016 9:08:50 GMT 1
Another method would be to set the left cylinder with a dial gauge to 27mm (half standard stroke) from TDC and check if the right is the same. If not, the crank is twisted! :-) This would allow for dwell.
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Post by steven on Sept 5, 2016 14:47:50 GMT 1
Another method would be to set the left cylinder with a dial gauge to 27mm (half standard stroke) from TDC and check if the right is the same. If not, the crank is twisted! :-) This would allow for dwell. ....you are still going to have to find TDC as your datum/starting point with this method, to then set 27 mm before or after TDC, so you are still going to incur the "dwell" that Bare mentions. As said previousely, a clock gauge/DTI and a rod/pointer/stick down the plug hole is the approved method for finding TDC, not only by Yamaha, but various other engine manufacturers. steven. |
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Post by bare on Sept 5, 2016 18:59:31 GMT 1
Wow.. complex setup pictured there.
BDC is easy-ish keep pushing down til it stops. Crank can still rock though.
Attach a CD size, or ideally larger degree wheel to the Engines' rotor, add a reference pointer.
Then do your TDC/BDC 'thing'
Observe how the degrees vary as one transits dwell areas. The crank rotates a discernable amount.. yet the piston does Not
Add the dwell for both pistons and a slight twist can be halved.. without realising it.
Always surprising , amusing even.. Given the Precise aspects some give to Ignition timing setup using Dial gauges.
Look at My Avatar photo.. That's exactly How I realised the flaws of the Dial Gauge technique.
IMO only reliable method to 'accurately' check crank twist (other than completely messed) is with the crank out on a bench on V blocks and 2 dial gauges on the crank pins.
Similar technique as any competent crank reassembler must do
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Post by muttsnuts on Sept 5, 2016 19:43:21 GMT 1
agree with bare, its the only true way to check unless its massively out, doing any type of check on a fully assembled engine is going to introduce error , unless its a long sway out, the chances of actually detecting for certain is hard to say as the dwell can also vary depending upon the wear in the small ends, piston skirt wear allowing for piston rock etc, all of thsse factors play into the checking on an assembled engine and none are easy to account for or allow. 1mm on the turn of the crank is a surprising amount of degress on the crank
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Post by wallcraft on Sept 5, 2016 21:00:52 GMT 1
So what's the symptoms on a running bike with a twisted crank with normal day to day running without thrashing it?
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Post by 4l04ever on Sept 5, 2016 21:04:58 GMT 1
Another method would be to set the left cylinder with a dial gauge to 27mm (half standard stroke) from TDC and check if the right is the same. If not, the crank is twisted! :-) This would allow for dwell. ....you are still going to have to find TDC as your datum/starting point with this method, to then set 27 mm before or after TDC, so you are still going to incur the "dwell" that Bare mentions. As said previousely, a clock gauge/DTI and a rod/pointer/stick down the plug hole is the approved method for finding TDC, not only by Yamaha, but various other engine manufacturers. steven. Not quite true....you do not need to find TDC, but only where the piston is at it's maximum height. It does not matter if the piston remains still while the crank moves for 1 or two degrees while you get your zero point, so dwell is completely eliminated this way. At half stroke (27mm) you are measuring where the dwell issue is at it's least, so this method should be the most accurate. Unless you need to measure how far out it is, you do not need a degree wheel or reference marks on the flywheel at all with this method. You will know if it is perfect, very close, or miles out, which is all you need to know really. |
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Post by steven on Sept 5, 2016 22:49:42 GMT 1
Wow, heavy duty crank shaft phase checking thread ! but all very interesting reading how others do it.
I have just done 16 hours work in the last 24 hour period, so perhaps not the best time to think about all this.
The comment.... "you do not need to find TDC, but only where the piston is at it's maximum height" threw me a bit....when the piston is at it,s maximum height, that is TDC !?!?!... is it not ?
So, obviousely lots of different answers on how to check the phasing of your crank shaft.
I understand that we all use our LC,s for different things, some like to race them and get every last ounce of power out them, and some like to tootle about the back roads on them on a sunny day, I fall into the latter group.
I agree with the above comments that the only 100% sure way to check the crank properly is with it out and on some V blocks etc.
But personally, on my 36 year old 2 stroke twin with its 180 deg crank shaft, I find the level of accuracy gained with two clock gauges poked down its holes more than adequate for my requiremnts, especialy if the alternative is pulling the crank shaft out it !
If its out by a measureable bit the clock gauges will show it up anyway, and if its out by a wasps wing, that my clock gauges dont show up, I,ll probably be none the wiser and still enjoy my sunny days runs around the back roads, feeling that all is well with the world.
steven.
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Post by 4l04ever on Sept 6, 2016 8:03:29 GMT 1
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Post by tsa on Sept 6, 2016 9:29:38 GMT 1
TDC is found by attaching a degree wheel to the flywheel and a steady pointer. Using a DTI get the piston to max height. Now rock the flywheel until the piston moves 0.1mm then note the degrees. Rock the flywheel the opposite way so you get the same 0.1mm and again note the degrees. NOw halve the difference in degrees is true TDC. This eliminates the dwell at the flywheel.
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Post by Tobyjugs on Sept 7, 2016 22:35:38 GMT 1
Wow we must be real enthusiasts because some of the comments made are very extreme. The comments bare has made you could also call inacurrate as there is also play or tolerances in the bearings that sit around the crankshaft.
Almost everything has a tolerance and if you are within this tolerance specified by the designer you will be ok.
I think it is a bit extreme to remove a crankshaft to see if it is twisted. In my opinion you can measure a twisted crankshaft accurately enough by finding TDC whilst the engine is still built up.
The best method i know for determining TDC is very simular to Kenny's advice;
Fit a pointer to your engine to use as a reference point for your timing wheel or fly wheel.
Put your DTI in the middle of the piston or along the center of the small end pin as this gives the smallest amount of rock when turning the engine.
Turn the piston up to where you think TDC is and calibrate your DTI to zero.
Turn the engine so that the piston moves down shall we say 1mm on the dial of the DTI. Then slowly turn the engine in the other direction so the piston moves back up until the DTI reads 0.15mm and note the degrees or mark your flywheel.
Carry on turning your engine slowly in the same direction. The piston will move up to TDC and begin to move back down again. We have only roughly set our DTI to 0 so it might go past 0, this is not important.
Because you have kept turning your engine in the same direction it goes through TDC and moves back down again and when the pointer reaches 0.15mm on the DTI stop and take note of the degrees or mark your fly wheel.
Just like Kenny said TDC is in the middle of these two readings.
You do not have to use 0.15mm i used this only for reference it can be 0.1 or 0.4 the choice is yours.
what i have quoted would be good enough for me but someone might say what about wear and tolerances etc. If your one of these people use the same method as above but in the other direction as well if the two lines are apart TDC will be in the middle of these lines
I have run my bike with a twisted crank and did not Know any different. It was only until i put it on a dyno and got advice from this forum that i inspected the crank.
I'm not a two stoke expert but i think a twisted crank would only alter the timing of the ignition which if goes the wrong way could be damaging, you may bad vibrations and as i experianced less power. I have wrote about it on here.
We all like to do the best we can with are bikes but i do think we are sometimes too extreme (me included)
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