Vintage Dirt Bike Q & A

I was at my cousin's house today riding four wheelers when he wanted to ride my 480. I told him once we got it off of my truck to make sure that he squirted some motor oil in there beforehand if he was going to use starting fluid to make it start faster. I told him to spray the oil in first to make sure that the piston didn't get scorched. He said no problem. I took off on his Raptor when he comes flying down the field and a few minutes later and the engine locks up. You can barely kick it over making me think that something is spun or out of alignment. When I asked him what he did, he said that he ran out of motor oil and that he squirted penetrating oil instead. He's going to pay to fix it but does anyone have any idea what he did? My friends tell me to put some motor oil in the cylinder and just let it set for a few days and see if the piston breaks free. I think its time for a new motor.

You either have a seized piston or bent rod. If I were you I would hope for the seized piston.

Starting fluid is a no no. Don't use it. The bike will start in less than five kicks if it is in good shape.

I am probably going with seized piston myself. When I spoke with the Honda mechanic, he said that the only way that I could do the starting fluid was if I used the oil overtop of the piston first. How much does it run to completely rebuild an engine?

Ouch! I feel bad for your cousin. Maybe you two should split the bill.

J

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

FWIW: I believe in warming engines up. The piston is often a high silicon content alloy in a cast iron sleeve. The two don't heat and expand at the same rate. I almost always run one of my bikes until I feel it is properly warmed up before I'll even let some knucklehead touch the throttle. This is from 40 years hard won experience: I have never had someone ride one of my bikes 'except a girl', warmed up or not, that did not immediate peg the throttle and see if they could get the front wheel off the ground.

Anyway, I looked on eBay.com for you. There are a couple of 480s being parted out right now. An air cooled cyliinder + piston with a starting bid of $9.95 and an NOS oversized piston for $9.95. They may be bid up a bit to the $50-$100 range but if I were you and either of them would work for you, I would consider getting a bid in.

I guess that we are going to probably going to just get it rebuilt by my neighbor. He has a shop that does a lot of ATV repair. He seems to know more about my motor than the Honda mechanic does... I think that I want to get the motor bored out and built up some. If the cylinder walls are scratched, I guess that I could get the cylinder bored .60 over. I found the cylinder on ebay from an 82 480 (my year). It says that the output shaft for the sproket is broke off. How hard would that be to fix? I guess that they could probably just take that off of my old engine?

To fix the output shaft you would need strip down both motors and transfer across the transmission - input shaft, output shaft, shift drum, forks and gears. I think it is recommended that you keep the gearbox as a set of "matched" components rather than just taking the output shaft on its own...

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

This is starting to suck. Would it just be easier to switch over to a CR500 motor and tranny? Probably cheaper in the long run and I could have a compression release switch. Top end speed would have to be better. What would be different? Has anyone done this before?

Now you're really talking about time and money. The only air-cooled CR500 was the 84 and the sprocket is on the otherside. If you go to a year above 84 you will have to also adapt the radiators and other stuff.

Bite the bullet and rebuild the CR480 or buy another used bike that runs.

J

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

Bite the bullet and get the original cylinder made "new". This may or may not involve a re-bore and re-plate (or have it sleeved) and a new top-end. I am guessing $250 which hurts some. Have a good shop do this and you will be set up for years, providing you check the piston and rings occassionally and remember to warm it up before riding. There are several 480s in our club and none needs more than a healthy kick to get going. Being shorter than the average bear I do this from a bike stand on the left-hand side of the bike. There is also a guy on eBay selling "new and improved" kickstarters for this bike that make it easier to get going.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

250 doesn't sound so bad of a price. I just dont want to have one thousand dollars in the motor to get it going again. I did love my dirtbike when it ran, and I always let it warm up too. When I did a compression test on it last it read 160lbs. Was that bad? From past dirtbikes, that was the lower "acceptable" range. Those however were 250s and not 480s. We are in the middle of haggling on the price of a rebuild, so I'll let you know how it goes....