What's this bolt for?

I'm pretty sure it's an oil check bolt, to make sure oil is getting to your top end, just want to make sure.

I'm hoping I can somehow make/get an adapter so I can put my acewell temp sensor in there to read oil temp.

http://www.xjbikes.com/Forums/viewtopic/t=38545/

Second pic of the right side of the engine, you'll see it a couple inches above the YICS port bolt. It has a phillips head in the bolt.

 

The purpose of that bolt has been debated before. One of my 550s doesn't have one there, one does. There is an undrilled "blank" on the one that doesn't.

Now that I think about it, I've never checked my spare 550 (YICS) cylinder head. If it has one, it should solve the mystery for us. I'll look this evening.

 

I believe I read that that, was what it was supposed to be for from my xs400 Service manual (It had YICS as well)

Let us know what you find Fitz.

 

So far as I know it is a plug bolt for the oil gallery that feeds the intake camshaft. Why it's a bolt instead of a plug is anybody's guess, only Yamaha knows for sure. I have only seen it on the 750 engine.

 

I have it on one 550, and not the other.

Still haven't had a chance to dig out my spare cylinder head; stay tuned...

 

OK; I have a HALF a definitive answer, but I think it's as good as we're gonna get.

I know for 100% sure where the bolt leads; and it is indeed an oil passage. Steve is right; that drillway, which is plugged on my earlier 550, is the horizontal component of the oil feed passage to the intake camshaft. (This was confirmed with some experimentation on my spare cylinder head.)

In the lubrication schematic, it's fed from the crank/mains, to both camshafts (individually.) So it's post main-bearings, pressure-wise; probably not the best spot to try to monitor oil pressure.

I suspect, but it's only a guess, that it's an oil "check" port or possibly a way to ensure that there is no air in the system in a freshly-assembled motor. More of a "bleed port." What leads me to that conjecture is the fact that it is the highest point in the whole lubrication system, coupled with the fact that it is indeed its purpose on the DOHC XS400 motor.

However, I checked the RK owners' manual against the RH owners' manual, and there's no added mention of it as part of the oil change procedure like there is in the 400 book. The fact that it's not included in any service procedures is what leads me to think it was a manufacturing thing, at least in the 4-cylinder bikes.

But this is all admittedly just supposition and a SWAG. All I can tell you for sure is that it is an oil passage; and one of questionable value as far as taking a pressure reading. But you can use it to be sure oil is getting to the head, at least to the intake cam. (If that was ever a concern.)

 

A temp sensor there would be a head temp, as the oil would have already picked up additional engine heat.

I'm thinking "oil temp" as " is the oil in my sump up to temp",
the probe needs to be in the sump for that.

 

I think BF has the correct answer, Yamaha may have done this to check for oil flow after the engines were assembled as Yamaha, for whatever reason, chose not to include an oil pressure sensor. As Yamaha found the oil pump drive to be reliable they phased out the bolt. This doesn't explain why my 82 650 didn't have the bolt/plug and my 1980 650 didn't have it.

 

I was thinking purely for a spot to put my temp probe for the acewell. It's meant for coolant temp, but I figure oil/head temp would be ok too), I guess i'll have to see if it will fit, or if i can make an adapter for it.

 

They didn't "phase it out" if anything, they added it. My '81 550 has a plugged drillway there; my '83 has the plug/bolt.

My '82 (non-YICS) 650 Seca just has a plugged drillway there.

Like I said; all we know for sure is where it goes. Yamaha would have to tell us why.