| Author | Message | ||
     Colintornado |
Looking in service manual under "REBUILD TIMING INSTRUCTIONS" it states to rotate the crank 270 degrees to go from front TDC to rear TDC. If the engine is a 72 degree vee surely it is 288 degrees rotation from front TDC to rear TDC ?(360-72 = 288) Was someone thinking it is a 90 degree vee or am I more stupid than I thought? | ||
| Motorhead102482 |
72 Degree V is the angle between the two cylinders in relation to the crank. TDC would normally be at the top of the compression stroke. You will feel the crank become harder to turn. It should be in between intake and exhaust cam lobes with some separation for that cylinder. 270 degrees must be where the rear cylinder comes to TDC. (Message edited by motorhead102482 on October 11, 2011) | ||
| Colintornado |
Its ok Motorhead I am not rebuilding,I was just reading the manual. The only way the crank rotation from front TDC to back TDC can be 270 degrees is if one crankpin was offset by 18 degrees. The 1125 crank is a single pin.Still think I am right  | ||
| Hootowl |
That is odd. 270 would be for a 90 degree V. Maybe Rotax lifted that paragraph from another one of their engine manuals before sending it over to the writers at HD, and didn't realize the numbers were different? | ||
| Motorhead102482 |
No, what i'm saying is the 72 degrees has nothing to do with timing. 72 degree V twin means that the 2 cylinders are set in a physical v formation angled 72 degrees from each other. Look at the letter V see how the two legs of the V come to a point. ok, so the engine is a V and the angle between the two legs (the cylinders) are located 72 degrees apart. 180 degrees wouldn't be a V twin. It would be a transverse engine. 2 cylinders would be a side by side or with 4 would be inline. 72 degrees is referring to the physical arrangement of the motor, not the timing. Ducati's L engine is 90 degrees hence an L instead of V twin because 90 degrees makes an L/ | ||
| Motorhead102482 |
270 degrees is referring to rotation of the crankshaft from TDC out of 360 degrees of a complete circle. Has nothing to do with 72 degree V twin engine configuration. | ||
| Ratbuell |
The crank still rotates 360 degrees per revolution, as noted above. Unless Erik has learned how to trim degrees, as a way to shed weight and help mass centralization!! | ||
| Hootowl |
So, regardless of cylinder angle, I can rotate from TDC on the front cylinder to TDC on the rear cylinder by rotating the crank 270 degrees? That makes no sense to me at all. What if the cylinder angle was 1 degree on a single crankpin twin? Still 270? How about a zero degree V? Still 270? I know that's not possible, but the math should still work. 360 minus the V angle should give you the number of degrees of rotation between TDC on each cylinder. Maybe I'm not thinking right. | ||
| Colintornado |
Hootowl,you are thinking right.I must admit it is hard to explain in words,If you turn your 1125 from tdc front by 270 degrees you will find the rear piston has not reached tdc. | ||
| Motorhead102482 |
I'm not agreeing or disagreeing that 270 degrees is the right answer for rear TDC, but engine rotation and 72 degree V have nothing to do with each other. I'm done at this point. Google V twin engine and maybe it can explain it to you. | ||
| S21125r |
Motorhead - not sure I follow you logic there but with a single crank pin, both cam and ignition timing are directly affected by the cylinder angle. So the tornado is correct. Front cylinder TDC compression to rear cylinder TDC compression should be 288 degrees and Rear cylinder TDC compression back to front cylinder TDC compression should be 432 for a grand total of 720 degrees. Offset crank pin is a different story though as you would need to know both the V angle and the pin offset to figure it out. | ||
| Motorhead102482 |
This is the easiest explanation I can give.  | ||
| Hootowl |
That has nothing to do with the question that was asked. | ||
| Motorhead102482 |
Crankshaft, camshaft and everything else tied to them (engine) rotation is what i'm referring to which has everything to do with this conversation and TDC and engine timing. I'm not talking about rotating the engine out of the frame. | ||
| Motorhead102482 |
Ok, think whatever you like. It's your bike. I'm done trying to explain this. I know engine angle correlates with engine timing. I'll work over here in my garage and let you guys figure it out in yours. Sorry I got involved in this conversation.} | ||
| Motorhead102482 |
I guess you're all motorcycle engine engineers at Rotax. | ||
| S21125r |
Motor, Would you agree that a parallel twin with a common crank pin fires one of it's cylinders every 360 degrees (assuming not big bang engine)? Now cant one cylinder by 1 degree. Cylinder don't fire every 360 degrees now. One fires at 359 degree spacing and the other at 361 degree spacing. Now expand that one degree cant to 72... | ||
| Hootowl |
Motor, you do know we're talking about the number of degrees between TDC on each cylinder right? No one is saying a circle doesn't have 360 degrees in it. | ||
| Motorhead102482 |
S21125r, yes i agree with you it could. But you guys are just speculating it. Just because it's a 72 degree engine, you don't subtract 72 degrees. You have to know more about the engine than just that. The manual should tell you how many degree of engine rotation are between TDC of the two cylinders. You would get close without needing to know all of the math involved if you set front to TDC, spin the engine around until the next compression stroke. Honestly, unless there's timing marks, I wouldn't do it without removing the spark plug. Even if it happens to be 288 degrees like you say. How are you going to know where that is without a degree wheel? | ||
| Clutchreaper |
I don't have the manual so I'm just going to make sure that what is being said is correct. You are saying TDC for both cylinders and that is what the manual said for sure? Just trying to make sure because I've worked on all sorts of different engines and some of them you are setting timing at a certain number of degrees before TDC. Just a thought on why it would be 270 unless it's incorrect. | ||
| Sparky |
I'm with colin. The manual came from Harley-Davidson, the same folks who gave us stators and voltage regulators that burn out. Everyone is entitled to make a mistake, but the honorable thing to do is to acknowledge the mistake and make restitution. Well, they haven't really fixed the stator thing (honorably) yet, so I wouldn't hold my breath on counting on a Service Bulletin correction to change 270 to 288. 270 degrees will get you close but you'll likely have to go a little bit further in order to find the spot where you can thread the Crankshaft Locking Tool into the rear TDC location on the crank. | ||
| Ratsmc |
"But you guys are just speculating it. Just because it's a 72 degree engine, you don't subtract 72 degrees. You have to know more about the engine than just that." Sorry, but this just isn't true. If you have a single crankpin, the v-angle determines TDC for both pistons and subtracting the V angle from 360 is exactly how you would determine TDC of one cylinder relative to TDC for the other cylinder. What other information do you believe is needed to know to determine TDC? | ||
| Colintornado |
Just so everone is clear, Erik Buell Racing have confirmed to me that 288 degrees is the correct amount of rotation from front TDC to rear TDC. So it is just a little missprint in the manual ie not 270. I suggest we correct the manuals and have a cold beer.  | ||
| Froggy |
They have done it in the past for various misprints or when a recommend torque spec is changed. The recently released a bulletin revising the correct readings on a voltmeter when testing stator output on the 1125. | ||
| Milt |
Froggy, Is there an "shop manual errata" section so that we can have one place to look for such misprints? I notice one at the top of a page describing an error in the oil change procedure, but no central repository - like "Error in the Manual". | ||
| Dannybuell |
great idea Milt. | ||
| Anonymous |
The manual was corrected in 2010 to read 288. |
