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R6 not firing 2 cylinders after rebuild

2K views 12 replies 3 participants last post by  jp129 
#1 ·
so I just got done with my rebuild on a "totaled" R6 I bought (great condition except needed new crankshaft), and when I start it up it runs but only on 2 cylinders. The 2 cylinders that fire are the center 2, the outer ones do not at all. I have replaced all 4 spark plugs with the same result as well as flipped around some of the ignition coils. Still only the 2 center exhaust pipes get hot. Is there a possibility that I did something wrong while rebuilding or is it electrical. Its a 2012 R6 with only 6000 miles on it.
 
#3 ·
I would start with the basic diagnostics for mis/non-fire (compression, spark, fuel).

1) Do a compression test to see what the cylinder compression numbers are
-If compression numbers are within spec and even across 4 cylinders, than your problem isn't engine mechanical - Check fuel and spark - move to number 2.
-If compression numbers are low, then do a leak down to to further trace the root of the low compression (head seal, valve seal, valve clearance potentially too tight, cam timing, rings, etc)

2) Check spark using in-line ignition spark test tool, you can also ground a spark plug but the inline tester is better
-If you have indication of ignition spark - Check for fuel - move to number 3
-If you don't have indication of spark, then check wiring harness/ecu (since you mentioned you swapped in plugs and moved ignition coils around and the problem did not follow)

3) Check each individual primary fuel injector connector using NOID light tester (you can make your own NOID light using a 12v bulb) to check if injectors are receiving ECU activation signal
-If NOID light is active for #1 and #4, then move your injectors around to see if they follow the problem - if they do, then replace injector
-If NOID light is inactive for #1 and #4, then check your wiring harness or ECU


Start here and see what you get, then others can help further refine the diagnosis. Sometimes I've seen these issues manifest itself due to bad/poor grounding, check to see how your grounds are.
 
#4 ·
I just ran a compression test on all 4 cylinders just by hand cranking the motor and the 2 center ones have 30psi and the outer ones have 0. I checked the valves on only the exhaust so far and there is no clearance at all on #1 and #4. (couldn't even fit a .10mm thru) so I'm guessing theres constant pressure on them which would result in no compression. I'm going to adjust all the valves tomorrow and recheck compression. For now I know it is a mechanical issue. I never checked the head on assembly because there was no visible damage.
 
#5 ·
I'm certain you're already aware a compression test by hand isn't as reliable or accurate as one on a starter, but it looks like it was able to point you in the right diagnostic direction already.

Good luck to you and report back if the valve clearance adjustments fixes your issue.
 
#7 ·
It's always a possibility, but I can't confirm or deny whether a bent valve would cause loose valve clearances. I don't have the experience to correlate the two events.

The best course of action would be to adjust the valve clearances to spec, then run a compression test. If the numbers are good, then it was simply a valve clearance issue. If the numbers are still low, then do a leak down to trace if the leakage is due to the valve seal.

If it is determined that the leakage is due to valve seal, it could be due to bent valve, burned valve, or damaged valve seat.
 
#8 ·
I pulled the head today and performed the old school trick of pouring some water down the exhaust/intake and seeing if it would leak through (obviously with the cams out). No water leaked through the valves at all. This tells me that the valves are in good shape but need shimming. Shims arrive Friday so ill have more updates then.
 
#10 ·
shimmed the head today and it fixed the compression issues. Still only hand cranking it but I'm getting the same Psi for all 4 cylinders now. 30PSI for all of them. Once I put the electric starter to it the psi will most likely be much higher. Shimming it seemed to be the most important piece. The motor did undergo and extreme over heating which is why it was "totaled" so that was most likely the cause. Thats also the reason one of the crankshaft journals was damaged.
 
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