yy250 blown head gasket! Argh..help! By beowulf101 (Read 1,251 times)

[beowulf101]

Ok here is the story.. I have a YY250t with 6500 miles on it. I was riding last week when it started making a god awful racket. I limped back to the house (less than a mile) and started looking at it. It would start, but with loud bangs, so I shut it down. I saw coolant dripping on the floor, so I suspected the worse. I pulled the head and yup – coolant in the cylinder – blown head gasket!. Well I finally found a new head gasket and installed. I hand rotated the piston to the highest point (couldn't find a TDC mark in the inspection port on the variator cover), replaced the head and reinstalled the cam shaft with the big hole straight up and the 2 small holes level with the edge of the head (used toothpicks to ensure they r as close to even as is possible!). I have put everything back together, but it will not start! Checked the spark plug (works) but it does not even try to turn over! Any suggestions? I am at my wits end!
Thanks guys!

[Alleyoop]

Did you check for compression, the rings could be shot.
Alleyoop

[tvnacman]

How does it sound when cranking , did you adjust the valves ? Have you checked for compression ? Do you have spark ?

John

[beowulf101]

Sorry guys, just got back into town... I checked the compression on PDB (poor dead beast) and got a reading of zero! Then I checked my new compression tested using the air compressor and it worked fine..so I would say that I have a BIG compression issue!.

When it started acting bad last week, I drained the oil and it looked like chocolate milk - so that meant that coolant leaked into the oil somewhere (I am assuming head gasket) and I actually saw coolant sitting in the cylinder when I pulled the head. So, I replaced the head gasket, put it all back together, and refilled everything, and ......no joy.......so do I need new piston rings? Can they go bad in only 6500 miles?

Thanks...oh, and I've never pulled a piston before...this could be a good time to learn!
Any advice guys?

[Cruiser]

If you saw liquid sitting on top of the piston when you pulled the head, then the rings are at least good enough to hold liquid. 6500 miles is not enough to wear out the rings. Broken rings are another story. Did you check the condition of the cylinder walls when you had the head pulled? If there were no grooves, then the rings might be OK.

You might have a problem with the head, but I would recheck the cam installation and timing before pulling the piston.

[new2scootn]

Check for bent valves? Also if valves are not timed properly you wont have compression. Liquid does not compress-wreaks havoc when gets into piston.

[beowulf101]

Ok so to test the "ring" theory, I removed the head and manually turned the piston to the LOWEST point it would go. I then filled the cylinder with oil to cover the top of the piston to a point I marked...and then went to bed. I wanted to see if the oil would "leak past the piston. When I went out to check this morning - the oil level was the same. So was this a valid test? Or just another brilliant but useless idea that proved nothing?

[beowulf101]

The continuing saga - I installed another new headgasket, and put the beast back together. I set the piston at TDC. installed the head, and put the cam shaft back in with the lobes facing down and the 2 small holes alligned with the edge of the head, . I then ran another compression check and got a reading of 30 - not good at all. Is it the rings or am i timing it wrong? This is so fustrating!

[Alleyoop]

When you checked the compression did you hold the THROTTLE WIDE OPEN if not you will get a low reading on compression. It needs to suck in as much air as possible.
Alleyoop

[beowulf101]

Thanks - so I tried it with the throttle full open, and still the same compression reading. I then removed the carb and got the same thing. Darned if I know what the issue could be. Is it back to the ring theory? Is there a way to check the new head gasket besides visual inspection?

[jct842]

A leak down test will tell where the problem is. Have seen plans on one forum or the other. In as few words as I can will relate what it consists of. you take air from your compressor piping it in to the spark plug hole through a measured orifice. With a gauge on the compressor side then the orifice and one more gauge before the spark plug hole tells you how fast air is leaking off.

The piston is at top dead center with the three holes in cam aligned. if you can hear air escaping in the carb the intake valve is leaking, in the exhaust pipe the exhaust valve is leaking, and listening at the oil filler the rings are leaking.

[Bashan]

Compression Test & Leak Down Tester