Bananas in the oil

When I hear Potassium, I immediately think of bananas.

I sent in the oil for an analysis on my Honda RC51 several times while I was riding it on track, 2020-2022. It always popped up as having too much Potassium in the oil (coolant). When the bike was up to operating temperature it smelled like a little kid had peed their pants; warm coolant. However there was never a drip of anything on the ground. So we (my dad and I) were thinking it’s a head gasket issue. The engine must be burning it up in the combustion chamber and shooting out the tailpipe. You’d think it would have white smoke coming out the exhaust, but we never saw any. The last time I rode it at a track day it drank the whole reservoir bottle in one day (seven sessions). Looking back now it drank about that much in the previous season.

Knowing that the RC51 has a coolant issue, I was going to bring it out to one of the track days this year (2024) and keep an eye on the coolant reservoir. I also poured some Ultra Violet (UV) Dye in the coolant, to help me verify where the coolant leak is coming from. The oil in the sight glass looked dirty (foreshadowing), weird, I usually change the oil at the end of the season. So, I warmed up my bike in the garage and drained the oil. It looked like McDonald’s Chocolate Milkshake was coming out. When your oil comes out looking like a vanilla or chocolate milkshake, you have coolant in your oil. My old 2006 Yamaha YZ450F taught me this. I’ve never seen this before on the RC51, things have gotten worse. Change of plans, I’m not bringing the RC51 to the track this year.

I took my UV Light and was searching all over the inside of each muffler. No fluorescent yellow marks. Hmm, I thought, maybe the combustion process burned up the dye also. Makes sense, but there’s got to be some that escape. Not every gasoline molecule gets burned up. And there’s a lot of coolant in the oil, the head gasket must have a large hole!

Forwarding to recent times. I dropped the oil pan this weekend. Luckily, I put UV Dye in the coolant before it last ran. This is what I saw:

You can see the vibrant yellow dots (drips) on the right hand side of the oil pan and the diluted UV dye in the oil at the bottom of the pan. If the coolant was coming from the head gasket, the drips would drop in the bottom of the pan, which sits under the cylinders, not on the right hand side; where the clutch and water pump are located. So I removed the clutch cover:

There’s UV Dye drops on the right side of the clutch, underneath the water pump. I think we’re on to something!

Oh, this reminds me to tell you about the time I had to replace the water pump seals just before the first time I ever took the bike out on track. If you don’t know my history of owning the bike, I will do it in as few of words as I can to catch you up to speed:

• Picked up a used 2001 RC51 with 32,XXX miles. Salvaged title. Carfax shows everyone from California to Washington has owned this bike. (Fall 2019)

• Checked the valve clearances and found that someone installed camshaft caps backwards on the front cylinder head. The plain bearings and camshaft journals were shot, making the cylinder head scrap. (early Winter 2019-2020)

• Got some used heads off eBay (front and rear). Took the best parts of each and built a good front and rear cylinder head. All the cylinder head exhaust valve guides were out of tolerance. Picked the best front and rear cylinder heads and replaced those exhaust valve guides. If you replace the guides, then you have to cut the valve seats for those guides, which I did. (late Winter 2020)

• Got the bike up and running, then coolant was dripping out the weep hole. Which meant the water pump seals needed to be replaced. So, I did. (Spring 2020)

Knowing the UV Dye looks to be coming from the water pump area, however, there is no coolant dripping from the weep hole. So, I pulled out my Endoscope. You can see there is no coolant coming out of the water pump drive, shaft or bearing. So the seal is still good.

However there seems to be coolant coming from the metal on the water pump drive housing.

It’s almost as if there is a crack in the drive housing.

Final Thoughts:

• If it is a crack in the water pump housing, did it come from pressing the water pump assembly with new seals into the right side engine case? I was following the Honda manual.

• I have an un-tested eBay RC51 engine in the garage!?!?

• Did idling this engine up to operating temperature with coolant in the oil ruin this engine?

• Should I take the right side engine case which includes the water pump, off the un-tested eBay engine and install it on this one?

• A Honda RC51 is not a fast bike relative to today’s bikes. However it’s the torque and the exhaust note that makes this bike such a joy to ride.

• This bike was designed to be on track, not sitting in someone’s garage. I want to get this bike track ready before next season.