new piston<<<<wont turnover

[3or4HONDA]

i have a buddy with an 04 yfz 450 and he recently put in a new std. bore wiseco piston. now when he trys to start it it will turn over a couple times and then stop like the battery is dead. well he charged the battery and it still does the same thing. even with the boost on the charger it will not turnover enough to start.

any suggestions?

maybe something to do with the decompressor? we triple checked the timing and know that is right.

[BlasterBTW]

Are the rings and piston in correctly? I have allready seen pistons put in backwards and the bike had these symptoms.

[3or4HONDA]

im pretty sure they are, this is not the first bike he has rebuilt. its like their is to much compression for the starter... i dont know, it will roll over a couple times then do nothin.

[#17YFZRACER]

try turning it over manually with a ratchet and see how it moves. maybe its binding somewhere

[ZRider400]

cam chain tensioner in properly? did he reset it so that it wasnt putting too much tension on it.........

[3or4HONDA]

ill tell him to check the tensioner, should it need to be adjusted if he just changes pistons?

[pgregg85]

Check the timing on the cams.

[Ride1Rob]

Is it a high comp piston? If so, that's your problem.

[3or4HONDA]

im not sure if it is or not, im not sure what he ordered. if it is tho what would he need to do? a better starter?

[Ride1Rob]

The stock battery cranking amps are too small for a hc piston. A 12.1 comp you can get by with but 13.1 and higher you'll have to either upgrade to the R1/CBR motorcycle battery or put in a kickstart. If you do the battery upgrade the battery box will have to be modified. Not hard just a couple of cuts to get it to fit.

[3or4HONDA]

well its running, we re-set the timing but then we had a problem with the TPS and we werent getting spark but got that figured out.

now....it seems to be running real lean
header is glowing, and its backfiring would the cold weather with an open airbox make it THAT lean?

i told him it was running lean this past summer so maybe the cold weather just made the problem more noticable...idk

:confused:

[3or4HONDA]

this 450 is for sale. runs good now but still has issues. starter will not push through compression even after decompression mechansim lets off some. brand new battery still wont, nothing is binding but he cant figure it out. needs a 450 expert i guess.

2500

[Ride1Rob]

Like I told you, you need to put a bigger battery with more cranking amps on it or a kick starter. The same OEM battery whether new or used is not going to turn it over for long.

[3or4HONDA]

y wouldnt a stock battery turn over a stock compression ratio...

[Ride1Rob]

So the piston is stock. My bad! Normally this happens with hc pistons bc of the low cranking amps on the OEM battery. Lower bearings and upper bearings seizing can cause this as well as a lack of lubrication to the piston. I've rebuilt a couple of motors where this was the issue. Did he check to make sure all the bearings were free of any binding?

[3or4HONDA]

it turns over fine and turns fine with the starter if the plug is out....so i dont know

[Ride1Rob]

Then it seems to be a compression issue. If it were bearings it would still be a problem trying to turn it over. Get a list of what he has done to the bike in terms of modifying it and also what all was rebuilt.

[3or4HONDA]

ya i told him to try and find his receipt to double check that a stock comp ratio was ordered and if it was then to have the starter checked.

[oemparts]

i have had a 13.5 comp. piston in my yfz for 3 years with the stock battery. i would say your problem is electrical if everything was put back together correctly.

[Ride1Rob]

You're the first that I've ever seen to run a 13.5 with the stock battery and never had problems. Been there and did that myself and had to eventually go to the R1 battery. Problem was solved after that.

[oemparts]

a few of my riding friends have hc pistons with the stock battery as well. i have read about upgrading the battery but never needed to do it.

[Ride1Rob]

I need to get in touch with whomever is putting yalls bikes together to see what their secret is lol. The problems that I've experienced on motors with the hc piston is not the initial fire up. But after firing the bike up several times it eventually drains the battery because it only has around 80 cranking amps. Everytime the battery would turn the motor much slower until it eventually stopped turning at all. The motorcycle battery has like 140/150 cranking amps, maybe even higher than that. I have also seen a couple guys get their motors built and think they have one thing only to find out they have OEM parts. Some shops are crooked and pocket the difference in the parts. Not saying this has happened to anyone here but be cautious of this. The best way to tell if you have a hc piston is to do a compression test. A hc piston is around 150psi as a stock piston is in the area of 125psi. Individual #'s will be different give or take. When I was running a hc piston, on the initial build it was 175psi. I was scared to try and crank the bike lol. Once the motor loosened up it dropped down to around 155/160psi.

[oemparts]

i work out of my garage and do alot of work on yfz's i have not had that problem with starting or has the other guys i ride with.