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I am rebuilding a 1994 Honda cr125r for a friend and it

I am rebuilding a...

I am rebuilding a 1994 Honda cr125r for a friend and it needs a new cylinder head but I can’t find one for it anywhere. I recently rebuilt a 99 and the cylinder heads look exactly the same so I thought maybe it would work but I didn’t want to buy it and it not end up fitting or something. I’m just trying not to spend $300 for a billet head.

Mechanic's Assistant: What is the model of your '94 Honda?

CR125R

Mechanic's Assistant: Are you fixing your bike yourself? What have you tried so far?

Yes I am. I put the original cylinder head on it and it started leaking coolant into the cylinder head.

Mechanic's Assistant: How old are the hoses? And have you tested the actual mix of your coolant?

The hoses are new. And the coolant is from a new bottle of engine ice

Mechanic's Assistant: Anything else you want the Mechanic to know before I connect you?

The guy he got the bike from ran it on straight gas instead of premix so I’m thinking the head is warped.

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Answered in 41 minutes by:
9/3/2020
Motorcycle Mechanic: Eric, Technician replied 2 years ago
Eric
Eric, Technician
Category: Motorcycle
Satisfied Customers: 1,592
Experience: MMI grad. 7 years experience in Honda, Suzuki, Yamaha, as service manager and tech.
Verified

Hello,

Coolant leaking into the cylilnder would be a result of the head being warped, or even the cylinder deck surface. In this scenario I would reccomend getting both the cylinder and cylinder head to a machine shop. They can mill off both of those surfaces, for likely the same price you would be paying for a replacement head. And doing this will ensure both surfaces are truly flat. Theres a chance if you bought a new head that the cylinder deck surface is warped and can distort your new head. Just find any good reputable machine shop and ask that those surfaces be planed off. Just taking off enough material to clean them up.

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Customer reply replied 2 years ago
These came off the bike.
Motorcycle Mechanic: Eric, Technician replied 2 years ago

After seeing the pics, there is one other item I would pay attention to. Those little divots in the cylinder head combustion chamber need polished down. Little spurs like those can get hot and cause knock. But again your best bet is to be sure both those surfaces are planed off. Or they may even have a lapping pad where it can be evened up. It would again likely be the same price if not cheaper than getting a new head.

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Customer reply replied 2 years ago
That photo was taken before I honed the cylinder. I forgot to mention. I think it has a sleeve in it but I'm not sure.The only other thing I could think of besides those things is that I put the head gasket on upside down the first time because it didn't have a marker on it that says which side is up.
Motorcycle Mechanic: Eric, Technician replied 2 years ago
From the photo it does look sleeved, where you see the different darker color of metal indicates this you can usually tell easier by looking in the ports, youd see again a difference in color of metal from the aluminum as well.
Having the gasket upside down likely wouldnt have caused a leak.
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Customer reply replied 2 years ago
I didn't leak before either. But I'm going to look into getting it resurfaced.It*
Motorcycle Mechanic: Eric, Technician replied 2 years ago
Also definitely look to polish down those bursts in the combustion chamber.
The only other thing would be if the head wasnt torqued down correctly. These head bolts need torqued down in a criss cross pattern in several stages before reaching final torque.
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Customer reply replied 2 years ago
Yea that's what I didThe manual call for 20 ft-lbs/240 in-lbs and I first torqued them in a criss cross pattern to 140 in-lbs then again at 240 in-lbs
Motorcycle Mechanic: Eric, Technician replied 2 years ago
Looks like it's best getting those planed off. They can even check those as well.
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Customer reply replied 2 years ago
I'm currently going to school for computerized manufacturing and machining and could do it at school but I would rather someone who has been doing it for years to machine them
Motorcycle Mechanic: Eric, Technician replied 2 years ago

Yep, especially a shop that is familiar with motor work, they would be able to do this easily

Eric
Eric, Technician
Category: Motorcycle
Satisfied Customers: 1,592
Experience: MMI grad. 7 years experience in Honda, Suzuki, Yamaha, as service manager and tech.
Verified
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