04 yfz450 low compression

busa4 · December 02, 2008, 12:09:21 AM

just picked up this quad and it wont start. checked for spark and its there. sprayed fuel in the carb and nothing. checked compression and im getting 35 psi while cranking. i know these things have an auto decompression system. is there a way to adjust or check it?

KnK Motorsports · December 02, 2008, 12:40:50 AM

The decomp system is on the cam, no way to adjust. 35psi is very low. put a little oil in the spark plug hole and then try the compression test again to see if the comprssion goes up, if it does then I would suspect that you need piston and rings and maybe a cylinder. where are you located?

busa4 · December 02, 2008, 01:35:06 AM

thanks. im in tampa. what is the compression suppossed to be when starting? what rpm does the decompression deactivate?

cutngrs · December 02, 2008, 01:36:15 AM

better yet do a leakdown on the motor start with piston all the way up to top dead center and try and find where the air is going could be a valve move the piston around and you will hear it though the pipe / carb / crank case this will almost alway tell you whats wrong valves or piston

busa4 · December 02, 2008, 11:28:41 PM

ok. tore it down and it is officially toast. the piston appears to be melted. im not sure if its from a failed cooling system or excessive piston to wall clearance. measured the cylinder and i got a shocking reading of 3.7667 inches (95.66mm)......damn! now thats worn. looks like a 1mm overbore here i come.

lugnuts · December 03, 2008, 01:43:10 AM

its still a good idea to check your valves even though you found the burnt piston the valves dont do well with overheating and they get worn over time and the valve sealing face goes away or gets dished and leaking valves can cause issues. and do yourself a favor and add the 07 oil upgrade to that engine it will pay you back in the long run

steve

busa4 · December 03, 2008, 02:27:33 AM

whats the oil upgrade? where can i find a tutorial?

lugnuts · December 03, 2008, 01:17:07 PM

it adds a oil nozzle to oil the wrist pin you need to use the 07 clutch cover and get the oil nozzle there are a few o-rings to replace and get the 07 oil pump also get new water pump seals and bearing and clutch cover gasket

steve

pm me your contact info I have a parts list for this as I have done several of these and just got the parts last week to do another

busa4 · December 03, 2008, 02:34:46 PM

sounds expensive. how much are we talking? does the engine have to be removed/disassembled?

01ZX12R · December 03, 2008, 03:51:10 PM

no the engine can stay in, you replace the right side outer case. real easy to do, and it is worth every penny. right at $300 for everything .

Miami450R · December 03, 2008, 04:28:26 PM

damn thats crazy!

my blown banshee had 80 psi lol

busa4 · December 03, 2008, 10:49:15 PM

next question. where can i bring my cylinder in for a bore and replating? i dont know of any local tampa businesses that do this. any suggestions? i want to keep it in state for a fast turn around.

Chillinthemost · December 03, 2008, 11:42:31 PM

I dont think you will find anywhere in Fl. that can do your cylinder. I also think the cost of boring and replating will approach the cost of a new cylinder. New cylinder should run you $225-$250.
As far as the oil mod, my 04 didnt have it, my 06 doesnt have it and both of these bikes have had a LOT of hours on them with no problems. I will be freshening up my motor this month and dont plan on adding the oil mod. I'm doing piston, rings, timing chain, and checking the valves.

scrimmy · December 04, 2008, 10:58:35 PM

if you need any parts let me know. i will save you alot of money

busa4 · December 05, 2008, 12:02:36 AM

Quote from: scrimmy on December 04, 2008, 10:58:35 PM
if you need any parts let me know. i will save you alot of money

thats what i like to hear. how much for the cylinder, piston and base and head gasket?

novadave · December 05, 2008, 01:56:55 AM

Check alba action sports for the cylinder. I got one for about $185 from them.

Chevy1500z71 · December 05, 2008, 02:52:27 AM

you should really find out what your problem is, why it melted a piston. we had a guy at work who insisted he will not pay us to clean his carbs on his banshee, that he would do it himself, we just put a whole new top end on it. he came back the next day all pissed off because its running bad. he ran it lean becasue he never cleaned the carbs and ran it all day, melted a hole in one of the brand new pistons.

busa4 · December 05, 2008, 12:44:04 PM

i agree but i have to get it running first. i already cleaned the carbs so my next area of interest will be the jetting. it has a GYTR exhaust. once i get it running i will check the cooling system as well.

scrimmy · December 06, 2008, 02:30:31 PM

pm sent