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Valve lash and carburettor settings are two of the most misunderstood and most critical mechanical adjustments for a smooth running boxer powered motorcycle.
Nothing will give you more grief than screwing up one or both of these adjustments. If you buy a second hand bike, these are two of the first things you should check out because I'd lay money on it that one, if not both adjustments, is screwed up and is a deciding factor in the previous owner's decision to part with an otherwise cool motorcycle.
Don't fear your toolbox!
You can do these adjustments yourself. Sometimes better than an authorized dealer. All it takes is a little know-how and a little practice. However, screw it up just a little bit by trying to set carburettors "by ear" and you tick off your respective Dnepr or Ural god and be banished to the chamber of fire (which won't be in your combustion chamber!).
I've either translated into English (old M-72/K--750 valve and carb settings) or straight up cut-n-pasted (newer Ural/Dnepr valve settings) so that most models are represented here. If you read through them, most are similar, however, some of the Dnepr OHV valve settings got overly complicated with the addition of a timing mark. They are all probably interchangeable.
Just remember: Set valve lash on a cold engine and carbs on a hot engine.
Setting Valves on a Sidevalve bike (K-750, M-72, CJ-750, MT-12 etc).
1. Turn the kicker until the INTAKE valve is completely closed. A gap must be visible (or "feelered") between the valve and the lifter. Set the gap on the EXHAUST valve to .10mm - .15mm. 2. Turn the kicker until the exact moment the EXHAUST valve begins to lift. Set the gap on the INTAKE valve to .05mm - .10mm. 3. Repeat on other side.
4. Turn the kicker and recheck measurements.
Setting Valves on a Ural 650cc Engine.
Taken directly from the 1998 Ural Owner's Manual:
Put a pan under the cylinder head, take off the head cap and drain off accumulated oil. Turn the crankshaft using the kick lever. Just when the intake valve begins to close, set the clearance for the exhaust valve and at the time the exhaust valve begins to open, set the clearance for the intake valve. Check the clearance between the larger end of the rocker arm and the valve stem. If the clearance happens to be larger or smaller than 0.05 mm/0.002 in, slacken off locknut and by turning the adjusting bolt in or out, set the required clearance with a feeler gauge. Lock the adjusting bolt with the locknut and check the clearance again.
Setting Valves on a Ural 750cc OHV Engine.
The thermal gap between valve stem and pushing arm of the rocker should be between 0.10 and 0.15 mm.
To adjust the valves, proceed as follows:
1. Revolve the crankshaft of the engine with the kickstarter pedal.
2. Adjust the gap for exhaust valve when intake valve starts closing, and adjust the gap for inlet valve when exhaust valve starts opening. Setting Valves on a KMZ/Dnepr 650cc OHV Engine.
This is the method given for MT-10 and MT-11 models (and I'd assume MT-16). However, one may get better results with one of easier methods that is not dependent on the timing marks which will also probably ensure there is a greater overlap of the valves. 1. Set the piston to the top dead centre of compression stroke by turning the crankshaft so that mark "B" on the flywheel is brought into coincidence with the mark on the engine crankcase; this must be watched through the peephole in the engine crankcase with the rubber bung removed.
2. In this position, both (inlet and exhaust) valves will be fully closed and their rocker arms must freely swing on their pins. Then, using a 0.07mm thick flat feeler guage, check the clearance between both rockers and valves. 3. In case the clearance is set improperly, slacken the lock nut and, rotating adjustment bolt in one direction or the other, set the required clearance. Following that, tighten up the lock nut. 4. The clearance is to be adjusted on a cold engine and must be equal to 0.07 mm. 5. To adjust the clearance in the other cylinder, turn the crankshaft by one revolution (by 360 degrees), following which check and adjust the valves as directed above. This is the procedure given for K-650 and MT-9 models.
1. Turn the engine crankshaft until the inlet valve closes (a certain clearance between the inlet valve stem and the rocker end must be well felt) (pushrod spin). In this position adjust the exhaust valve clearance to 0.07mm. Then continue to turn the engine crankshaft until the exhaust valve starts to lift and set the inlet valve clearance to 0.07mm.
2. Repeat on the oppozite cylinder.
3. The clearance should be adjusted on the "cold" engine. The clearance should be 0.07mm.
4. If there is no clearance or the clearance is too small, the valve will not tightly fit the seat at the instance of closing; if the clearance is too large, valve opening will be retarded.
CARBS.
Nothing is so critical on BMW boxer styled engines as carb balancing.
The methods below have beed translated and/or adapted for use with modern carbs from one general method from old BMW R-71 and Soviet M-72 manuals. You probably cannot find it so easily outlined anywhere else on the web in English. This method is idiot proof and has been in use for generations. If you can tell when an engine is at maximum and minimum revs, you can easily and accurately set the idle and balance on your carbs.
Setting your carbs properly is a two step process.
First, you set the idle using the adjustment screws. The adjustment screws only affect the idle speed!
Then, you must sync the slides to make sure both heads on your engine are running at the same speed at the same throttle position. Basically, you want to ensure that one jug is not running at 30MPH while the other jug is running at 50MPH.
If it is your first time trying to set your carbs, you may want to set up a fan to keep your engine cool. Once you understand what you are doing, the whole process can be done in less than 10 minutes.
A word about carb balancing tools.
I think the speedometer and not the Twin Max should be the gold standard to judge balancing by.
I've never used one before, but I feel balancing tools may not really give an indication of real-world performance based results in all situations (mostly with a crappy old bike or one not fully broken in). Sure, balancer gauges probably work fine, but they only prove each jug is pulling the same torr (mmHg/vacuum). I just think the best way to measure the real result of what each jug's true output is best done somewhere after the crankshaft (like the speedometer!!!). It just makes sense to me that you can't get no better sync-ed as long both jugs are running individually at the exact same speed at the same throttle position.
A balancing tool assumes identical inputs of air in each jug will result in identical outputs on the crank. I'm saying that might not necessarily be true in all cases because there's probably lots of crazy stuff that can go on in each jug of a Ruskie engine besides air flow. Sure, sure both jugs are pulling the same vacuum on each carb, but more importantly, is each jug pulling an equal load in relation to the other? Using a balancer assumes that there are equal conditions in both heads. There's just too many variables: spark plugs, HT wires, hot spots in the cylinders, cylinder compression variance, crud on a jet, valve leakage, etc.
I still think you should do a genuine power check to confirm the carb balancer results.
Food for thought: You can bet there's not a single Twin Max in China or the former Soviet Union.
Setting K-301/K-302/K-37 Carbs.
1. Warm up the engine (make sure both sides get hot because many times bikes are only running off of one cylinder). Retard the engine if you have manual advance. If installed, disconnect the supercharger hose and plug up the carb holes or as my lazy arse would do, pinch off the tube with vise-grips so that absolutely ZERO air passes from one side to the other. Then, kill or ground out one cylinder; we'll set the carb on the other cylinder. 2. Loosen the carb neck screws so that there is slack between the end of the cable casing and the carb neck. 3. Loosen the jamnuts on the HORIZONTAL (mixture) and DIAGONAL (slide lift) adjustments. 4. Screw the HORIZONTAL screw all the way in. 5. Set the DIAGONAL screw for minimum steady operation. 6. Adjust the HORIZONTAL screw for maximum engine speed. 7. Set the DIAGONAL screw for minimum steady operation again by backing it out. 8. Tighten jamnuts. 9. Repeat for the other side. 10. Note differences in engine speeds when operating on single cylinders. Plug up both cylinders. Adjust the DIAGONAL screws equally for final low speed idle operation. 11. Tighten jamnuts. 12. Put it on the center stand (or jack up the drive wheels on an MT-16) 13. Fire it up, 14. Put it in 4th gear (might wanna chock it), 15. Rev it up to 30-40khp, 16. Clamp/hold the throttle in place, AND DO NOT CHANGE UNTIL THE PROCEDURE IS OVER 17. Disconnect (or ground) one cylinder wire, 18. Note exactly what the speedometer settles down to after 10 seconds 19. Now quickly re-connect that side disconnect the other (don't move the throttle even though it'll rev up some) 20. Adjust the carb cable ferrule on the running side to match the exact speed you noted while the first side was running. 21. Now let off the throttle and reconnect your supercharger. Setting K-68 Carbs.
Instructions based on revising the generic K-301/K-302/K-37 instructions above. Tested on my personal bike and it works great.
1. Warm up the engine (make sure both sides get hot because many times bikes are only running off of one cylinder). Retard the engine if you have manual advance. If installed, disconnect the supercharger hose and plug up the carb holes or as my lazy arse would do, pinch off the tube with vise-grips so that absolutely ZERO air passes from one side to the other. Then, kill or ground out one cylinder; we'll set the carb on the other cylinder.
2. Loosen the carb neck screws so that there is slack between the end of the cable casing and the carb neck. 3. Note that it is now VERTICAL (mixture) and HORIZONTAL (slide lift) adjustments.
4. Screw the VERTICAL screw 1.5 turns out from a softly seated, fully in position (if already idling at all, skip this step). 5. Set the HORIZONTAL screw for minimum steady operation. 6. Adjust the VERTICAL screw for maximum engine speed. 7. Set the HORIZONTAL screw for minimum steady operation again by backing it out. 8. N/A. 9. Repeat for the other side. 10. Note differences in engine speeds when operating on single cylinders. Plug up both cylinders HT cables. Adjust the HORIZONTAL screws equally in 1/8 turns for final low speed idle operation. 11. N/A. 12. Put it on the center stand (or jack up the drive wheels on an MT-16) 13. Fire it up, 14. Put it in 4th gear (might wanna chock it), 15. Rev it up to 30-40khp, 16. Clamp/hold the throttle in place, AND DO NOT CHANGE UNTIL THE PROCEDURE IS OVER 17. Disconnect (or ground) one cylinder wire, 18. Note exactly what the speedometer settles down to after 10 seconds 19. Now quickly re-connect that side disconnect the other (don't move the throttle even though it'll rev up some) 20. Adjust the carb cable ferrule on the running side to match the exact speed you noted while the first side was running. 21. Now let off the throttle and reconnect your supercharger. Setting K-63/K-65 Carbs. Instructions based on revising the generic K-301/K-302/K-37 instructions above. No reason for it not to work great.
1. Warm up the engine (make sure both sides get hot because many times bikes are only running off of one cylinder). Retard the engine if you have manual advance. If installed, disconnect the supercharger hose and plug up the carb holes or as my lazy arse would do, pinch off the tube with vise-grips so that absolutely ZERO air passes from one side to the other. Then, kill or ground out one cylinder; we'll set the carb on the other cylinder.
2. Loosen the carb neck screws so that there is slack between the end of the cable casing and the carb neck. 3. Note that both adjustments are vertical screws. It's now LOWER (mixture) and UPPER (slide stop) adjustments.
4. Screw the LOWER screw 1.5 turns out from a softly seated, fully in position. (If the bike is already mostly running, it is not necessary to "pre-set" this screw, simply adjust when you get to Step 6.)
5. Set the UPPER screw for minimum steady operation. 6. Adjust the LOWER screw for maximum engine speed. 7. Set the UPPER screw for minimum steady operation again. 8. N/A. 9. Repeat for the other side. 10. Note differences in engine speeds when operating on single cylinders. Plug up both cylinders spark plug cables. Adjust the UPPER screws equally in 1/8 turns for final low speed idle operation. 11. N/A. 12. Put it on the center stand (or jack up the drive wheels on an MT-16)13. Fire it up, 14. Put it in 4th gear (might wanna chock it), 15. Rev it up to 30-40khp, 16. Clamp/hold the throttle in place, AND DO NOT CHANGE UNTIL THE PROCEDURE IS OVER 17. Disconnect (or ground) one cylinder wire, 18. Note exactly what the speedometer settles down to after 10 seconds 19. Now quickly re-connect that side disconnect the other (don't move the throttle even though it'll rev up some) 20. Adjust the carb cable ferrule on the running side to match the exact speed you noted while the first side was running. 21. Now let off the throttle and reconnect your supercharger. |