I did a top speed run on my ct3 forgot to check my oil tank.  The trail-tech gauge I was using was working only intermittently so I don't fully trust it. But during this run I saw temps peaking around 500 degree.  There was an engine stumble or two.   I got off the highway and rode home without issue.

A week later, I took the head off and saw the gasket and been damaged.   The round edge of the piston skirt also has some odd damage but don't know if that occurred earlier.      Would you please take a stab at explaining how this happened?

Just the heat?  Over-tightened the head bolts?   This happened a month ago so I don't remember if this happened before or after I set the needle clip on the second from top position from the center. Before I made that change the engine was running a little lean at wide-open-throttle but not going over 400 degrees.

I used a borescope and saw one flake of copper at the bottom of the crank area but I did see quite a bit of grit and tiny particles inside the holes inside the crank lobes.    The crank also has some mild surface rust.

Does that level of contamination require a case splitting to clean or can I get away with removing the engine and flushing out the detritus?


 

 

 

That's an odd thing to happen. Is it possible someone's used a 125 head gasket by mistake, I doubt what i'm saying as 56mm is a hell of a long way from 66mm but 'would' bolt straight on. Actually the more i look at the pic i now 'do' think that's what's happened as isn't sitting far enough out on the head surface.

was initially thinking big end cage but not--i stick with head gasket being 125. In theory-- wonderful thing theory haha--the shrapnel should have gone out the exhaust port & not down the bottom but there would've been a hell of a lot of it trying to get out. Or they'd trimmed the excess off but piston still found some at the edge of the squish to play with. Actually just looking again i can see 56mm mark in the head where it originally overlapped. I now see you fitted it so go stand in the bad boy corner haha. I reside there permanently as always doing something wrong that i'll never do again so i'll see you there!!. I'd just put it back together & go ride. Have a happy day.

It is possible I ordered the wrong gasket. I've done it before. Middle-age is started to take hold.

Thanks for responding!

I checked, babbits lists the same two head gaskets for the AT3 and CT3. I guess did a einy-mieny-miny-moe when selecting.

248-11181-00

251-11181-00

 

Sounds to me like you went the wrong way with the needle clip, and made it even leaner.
As RT325 said, that's the wrong gasket .... you need the 251 gasket

Lastly I worry that you may have damaged the rings if you were reaching into the 500 degree range
Speaking from experience, that kind of cylinder head temps, can take the temper out of them . . . 
Since I'm not there to evaluate, I'd recommend that you replace them just to be on the safe side.

 

very interesting

you stated "forgot to check my oil tank"....did engine run out of oil?

The too small head gasket makes sense. I recently bored an R5 to 1.5mm over and was warned to trim head gasket if it exhibited what I think your picture shows.

If bore looks nice, then I would clean up piston with some 400 and put back together with correct jetting and roll!

Hi Dave, 

I just brought a new piston and rings from you two weeks ago.1st o/s,  It's getting bored out now.

I was playing around a lot with the carb.  Recently when opening it up, I wound up bending the float arms and had to spend some time tweaking them back into spec.  Before I found out that the stock needle setting was two from the top, I was usually running in the center. and a couple of times tried 4th from top.  

Rob

Same old problem discussed on here about 1000 times.. Yamaha had "shared" parts lists in the early days. For example, 125 and 175 shared the lists as they are very similar bikes. Unfortunately, the tables and identifiers in the original parts books got lost in translation to the online digital lists.

If you see two listings for the same part in a list like you did, most of the time you can select the correct part by using the first three digits of the part number or "model code" .

There are model code lists in the Tech library... 248 is an AT1, 251 is a CT1... so you need the gasket part number that starts with 251 for a 175

It was well below the level glass but I don't think it was bone dry.