Fresh rebuild, crank but no start

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mmxchamp · #1 Post by **mmxchamp** » Mon Dec 21, 2015 5:38 am

Hey guys, looking for some help here. Fresh rebuild (head redone by Dave, balanced crank and z400 bearing, etc) but I'm getting a crank but no start. I tried a bunch of stuff today and got it running at one point, but when I put plastics on and went to actually ride it I'm right back at crank but no start condition. Things I've tried already -

Spark - looks good, tried swapping coils with spare but no improvement
Timing - key good, c lines up at TDC checked with a screwdriver down the plug hole
Fuel - definitely getting fuel, perhaps too much? After a few tries at cranking if I pull the plug there's a layer of gas on the piston and some on the plug too. I did pull the intake and the spray pattern looked ok
Compression - tried adding 1-2 tbsp of oil, it smoked a bit and did start up after 2 attempts with cleaning of the plug between, but I tried adding some again and it doesn't seem to help.

I'm not sure where to go next, seems like excess fuel might be an issue but I'm not sure - repeated attempts at cranking might just cause that to happen?

POWER MAD MAN · #2 Post by **POWER MAD MAN** » Mon Dec 21, 2015 7:25 pm

First I would check compression, if lower than 70 pounds you need to tear motor out. If compression is good then I would check your tps sensor, and also don't give throttle while starting or you will flood it badly.

mmxchamp · #3 Post by **mmxchamp** » Mon Dec 21, 2015 7:47 pm

Yea, I'm gonna have to pick up a tester with the right size adapter - the standard rental from the Autoparts store didn't have the right size plug adapters :-(
TPS Seems to be reading well, I can monitor with my DM kit. I believe I got it set correctly, I followed the directions found on here.

I'll tackle it again after work today; I was pretty angry last night but I've calmed down a bit.

MX Quad Dad · #4 Post by **MX Quad Dad** » Tue Dec 22, 2015 12:45 am

You said you checked TDC thru plug hole. Was the keyway straight up? key lineing up with the "C" only indicates flywheel has not spun, key could still be sheered.

mmxchamp · #5 Post by **mmxchamp** » Tue Dec 22, 2015 1:26 am

Keyway should be good - I pulled the flywheel and the key is fine, no damage to it.

After work I went and picked up a compression tester that actually has adapters for small plugs - checked on my DR650, ~85 PSI. The cannon was at ~10 PSI dry, and I added some oil and got it up to maybe 30. Definitely low :-/ So, working on pulling it all apart again. Is it possible its just timing, or am I gonna have to pull the head and look at the rings and all that jazz?

POWER MAD MAN · #6 Post by **POWER MAD MAN** » Tue Dec 22, 2015 2:27 am

It might be timing but I would also check your valve clearances.

MX Quad Dad · #7 Post by **MX Quad Dad** » Tue Dec 22, 2015 3:19 pm

How did it run when you had it running? How long did you let it run?

mmxchamp · #8 Post by **mmxchamp** » Tue Dec 22, 2015 3:36 pm

It seemed to run fine, it didn't sound very abnormal. I only let it run for 30 seconds or so - closed garage cause it's cold outside!

I was wondering how it's possible to have it start at all if my compression was so low, but I'm pretty dang sure the compression tester is good - checked on my dirt bike. I did add oil a bit before I got it to run, but I added oil during the compression test too. Kinda strange.

wistech · #9 Post by **wistech** » Tue Dec 22, 2015 4:36 pm

Piston installed backwards and bending valves. Sticking buckets cam timing way off and bent valves. Rings not gapped before install and galled the sleeve. Piece of dirt in a valve seat. Decomp broken or stuck. Apply air pressure at tic and see where the leakage is

mmxchamp · #10 Post by **mmxchamp** » Tue Dec 22, 2015 4:48 pm

I turned the crank a bunch of times before engine install to make sure the valves were all good, didn't hear anything so I hope I got the piston installed correctly. I'll pressurize at TDC and see where she leaks.

Thanks for all the help - I've rebuilt this engine twice so far; failed once after the case cracked (still not sure how...) and then a circlip came off one of the small oil pump gears and got up in between the cam idler gear and intake cam; sheared the water pump impeller end off and trashed most of the intake side of the head - current head is a rebuild from a spare engine I had.