1989 Engine Rebuild Questions

[btoldi]

I said this in my introduction, but I just got a 1989 KDX200. After getting it home and taking a closer look, I found out that the remaining oil was super milky and thick and there was oil in the radiator. So the plan is to tear down the motor, split the case, replace all the seals and gaskets, give the motor a good thorough cleaning and check for other surprises. I've rebuilt a few dirt bike motors in the past but not to this extent. My main question is if the oil looks like very thick milk (its a weird description but that's the best description ha), is there anything specific I definitely need to replace while I have the cases split? Should I go ahead and spend the money to do a complete bottom end rebuild or just take a close look at bearings and components then decide if they need to be replaced?

[Slick_Nick]

Figure out where it's coming from for sure. Likely the head gasket.

[Molly's 70]

So you are saying the transmission oil is milky & oil in the cooling system?

[Slick_Nick]

Sorry, maybe I misunderstood you. If it's transmission oil in the radiators it might be a water pump seal.

[btoldi]

Yeah, from what it looks like the transmission oil has mixed with the coolant. So when I drained the oil it was milky and thick and then I drained the radiators and it was a mix of milky oil and water. From what I have read I think it might be the water pump seal but the previous owner said he had head gasket problems so I'm not positive yet. Either way I plan on replacing all the seals and gaskets but I'm not sure about the best way to fully clean the case and what other parts (bearings, internal components, etc.) I should go ahead and replace while I have the case split.

[Molly's 70]

Sounds like the oil seal, and/or the mechanical seal, in the water pump failed. They can sometimes be damaged installing the pump shaft. (ask me how I know)

I'd flush the engine & rebuild the water pump & see what that gets you. Or you can rebuild the engine, it's always a fun project.

[KDXGarage]

Take the head to a machine shop to see if it is flat on the bottom.

[Slick_Nick]

Take the head to a machine shop to see if it is flat on the bottom.

Or a quick check on the kitchen granite countertop would let you know if you're in the ballpark.

[Molly's 70]

Take the head to a machine shop to see if it is flat on the bottom.

Or a quick check on the kitchen granite countertop would let you know if you're in the ballpark.

Or a piece of glass & a feeler gauge. .002 feeler gauge.

[85' kid]

I have a 91 that has milkshake throughout the engine as well. If its getting into the tranny is gotta be crank seals, I'm not a master with kdx's but from the brief knowledge I have I would say it defiantly cranks seals and head gasket, that's the only way it could be letting water into the bottom end. Actually it could also be the gasket that goes between the cylinder and the crank case, but its for sure crank seals, cause no matter where the waters is coming in its getting into the tranny. Im just going to buy the complete gasket and seal set, its only 60 bucks on ebay. https://www.ebay.com/itm/264714182670

[btoldi]

I'd flush the engine & rebuild the water pump & see what that gets you. Or you can rebuild the engine, it's always a fun project.

When you say flush the engine, how would you suggest to flush it? I know you can fill it up with oil, run it till it gets up to temp, change the oil and then repeat till its clean, but is there another way of flushing the engine?

[Molly's 70]

If it were mine, I'd put the engine in the solvent tank. (Drain the oil first.) Put the solvent nozzle in the oil fill hole & start flushing. Put your finger on the oil drain hole to regulate how full the crankcase gets then release. Repeat till your happy.

You could set up some kind of make shift solvent deal if you don't have access to a tank.

[Slick_Nick]

Splitting the cases is not difficult, I'd recommend just doing it properly.

[btoldi]

If it were mine, I'd put the engine in the solvent tank. (Drain the oil first.) Put the solvent nozzle in the oil fill hole & start flushing. Put your finger on the oil drain hole to regulate how full the crankcase gets then release. Repeat till your happy.

You could set up some kind of make shift solvent deal if you don't have access to a tank.

Is there any specific solvents or kinds of solvents you would recommend?

[Molly's 70]

Just regular automotive solvent. Most are non flammable these days. Any auto parts stores should have some along with a solvent tank if you need one. It might be cheaper & easier to just go to your local auto or cycle service center & ask if they can do this for you.

[bufftester]

If you have oil in your radiator, then the water pump seals are bad. If you have coolant in your transmission, then the water pump seals are bad.

If you have bad compression, idle issues, oil in the flywheel cover then you have bad crank seals. Bad crank seals won't let oil into your coolant or coolant into your oil.

If you have a coolant smell to your exhaust then you likely have bad cylinder gaskets or a cracked cylinder.

Regardless, if you have had coolant in your oil the seals and bearings need a good look which means opening the cases. And wih oil in your coolant you're going to need to at a minimum take off the jug, so may as well do a full rebuild IMO.

[doakley]

To answer your original question, if you are going to split the cases, replace everything, all bearings and all seals.
I’m just not sure you need to slit the cases.