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Old 04-30-2010, 10:50 PM   #1 (permalink)
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raced a 1.5 hour hare scramble, afterwards found my head and cylinder gaskets were leaking antifreeze. replaced the gaskets, now i have no compression. i thought maybe the rings (piston) went bad when i took the cylinder off so i bought new rings, installed them, still no compression. does anyone have any suggestions as to what may be the problem or things i should check? here is some information that may be helpful to you guys.

-i did find myself over-revving in the race (hence the leaking gaskets)
-cylinder and cylinder head are torqued correctly
-spark plug torqued correctly
-i have not adjusted my valves since the race
-valves are in working condition however and do not seem to be leaking
-for some reason, (head is off) while looking straight down at the piston inside the cylinder, (facing as if your riding the quad) the piston (not rings) sits to the left of the cylinder

sorry if my description is hard to understand, tried to make it clear as possible ... tomorrow in the daylight, i will see if i can get some pictures up for you guys. thanks for any advice and help that leads to a solution!!
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Old 05-01-2010, 04:23 AM   #2 (permalink)
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Sounds to me like the auto decomp on the cams is staying open. Pull the cover n see, if they feel fine, pull them out, if it gains compression then either cams or messed or valve adjustment way off. If still no comp a valve is bent or about to drop or the rings are installed completly wrong or the heads warped hard.
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Old 05-01-2010, 09:45 AM   #3 (permalink)
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its an 04 did the decompresion plug come out of the head?
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Old 05-08-2010, 04:06 PM   #4 (permalink)
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sorry i havnt gotten back to you guys with any information. i've been extremely busy with work and trying to grad. college. anyhow, i checked the valves, theyre not bent. also checked to see if any are leaking and that turned out good. also sprayed windex around cylinder and cylinder head gaskets and turned the motor over ... no bubbles, so i know the head or cylinder isnt warped. lbyfz450, whats this auto decompression your talking about?? and atvlifestyle, the decomp. plug is still in, however, im not sure if the gasket it worn on the inside or not. if i do the same technique with the windex on this part will it be effective on see if this is the problem?? any other suggestions as valves are ok and no warping? also, regarding the rings, i believe i installed them right ... went according to the manual
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Old 05-08-2010, 04:14 PM   #5 (permalink)
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On the exhaust cam there's an auto decomp. If u look on the cam gear there's a little spring and lever, does it move freely? If u look on the cam there's s pin that will come In and out
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Elka triple rate front & back, Houser +2 arms, +1 swinger & +2 stem, G-force axle, Streamline lines, wave rotors, AC nerfs, IMS pegs, douglas beadlocks, MXR6 tires, Pro taper bars, ASV levers, Gibson stablizer, MP twist.
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Old 05-11-2010, 03:58 PM   #6 (permalink)
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QUOTE (lbyfz450 @ May 8 2010, 04:14 PM)
Quote:
On the exhaust cam there's an auto decomp. If u look on the cam gear there's a little spring and lever, does it move freely? If u look on the cam there's s pin that will come In and out[/b]
its not hanging freely or anything. im not sure how stiff the spring tension is suppposed to be but it doesnt take much effort to move it. however, there is enough spring tension to hold it in place.
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Old 05-11-2010, 05:06 PM   #7 (permalink)
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check the valve clearance :
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Old 05-12-2010, 10:31 PM   #8 (permalink)
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lol is your rod connected to your piston? sorry lol.

but are you sure your piston and head are true, hav you pulled your plug and checked to see if your gettin and compression at all?
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Old 05-13-2010, 11:51 AM   #9 (permalink)
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QUOTE (climb-101 @ May 11 2010, 05:06 PM)
Quote:
check the valve clearance :[/b]
i have not checked that yet, and it most likely is off, as i said i was over-revving throughout the 1.5 hour long race. but what does valve clearence have to do with compression if i already checked for leaks within the valves?
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Old 05-13-2010, 11:54 AM   #10 (permalink)
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QUOTE (westboy-yfz @ May 12 2010, 10:31 PM)
Quote:
lol is your rod connected to your piston? sorry lol.

but are you sure your piston and head are true, hav you pulled your plug and checked to see if your gettin and compression at all?[/b]
lmao, before i opened the reply i was hoping you werent serious. ... but, what do you mean the piston and head are true? i dont have a compression tester that will fit my spark plug threads. but i did put the whole motor back together, put my hand over the exaust port and cranked the motor over. there was some air being forced out, but nothing near what it should be
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Old 05-13-2010, 01:42 PM   #11 (permalink)
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QUOTE (yfzstar @ May 13 2010, 09:51 AM)
Quote:
but what does valve clearence have to do with compression if i already checked for leaks within the valves?[/b]
since you had the head off, one of the shims could have slid out of place under the bucket holding open a valve when the cams are put into place. That will cause a huge leak for the compression to leave the cylinder.

checking the valve crearance will tell you if this is what is happening.
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Old 05-13-2010, 02:04 PM   #12 (permalink)
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well this kinda the same thing happened to me, i didnt get the coolant top all the way on there and while doin wheelings all the coolant came out, resulting in a scourched piston and warped head. i put a new piston in because it was not true to the head (the whole thing piston top shrank.) i also got my head plained. and it was ready to go after that.

just some things you might look at. hope it helps
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2005 YFZ 450
480 Athena big bore
4th clip
212 main/48 pilot
Sparks full system exh.
Port & Polished
HC stg. 3 cams
Zip TY needle
ESR intake

ITS MEAN WHEN THE LIGHT TURNS GREEN

BAD COMPANY RACING
#6T9
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Old 05-17-2010, 11:24 PM   #13 (permalink)
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QUOTE (westboy-yfz @ May 13 2010, 02:04 PM)
Quote:
well this kinda the same thing happened to me, i didnt get the coolant top all the way on there and while doin wheelings all the coolant came out, resulting in a scourched piston and warped head. i put a new piston in because it was not true to the head (the whole thing piston top shrank.) i also got my head plained. and it was ready to go after that.

just some things you might look at. hope it helps[/b]
does help! i guess buying a piston is gonna be my next move if i adjust the valves to the right clearence and there is still no compression. by making the head plain, what are you exactly talking about? can you spell out the process?
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Old 05-17-2010, 11:31 PM   #14 (permalink)
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I think he means milled or resurfaced to make sure it isn't warped from the overheating.
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Old 05-18-2010, 01:00 AM   #15 (permalink)
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QUOTE (westboy-yfz @ May 13 2010, 12:04 PM)
Quote:
well this kinda the same thing happened to me, i didnt get the coolant top all the way on there and while doin wheelings all the coolant came out, resulting in a scourched piston and warped head. i put a new piston in because it was not true to the head (the whole thing piston top shrank.) i also got my head plained. and it was ready to go after that.

just some things you might look at. hope it helps[/b]
never seen a piston shrink. dont even know if that is possible.


QUOTE (bigblockbanshee @ May 17 2010, 09:31 PM)
Quote:
I think he means milled or resurfaced to make sure it isn't warped from the overheating.[/b]

x2. take it to any good machine shop in you town and they should be able to mill your head for ya. the normally warp under the exhaust port
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