Author Topic: #7 joins the fleet  (Read 11059 times)

fret not

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Re: #7 joins the fleet
« Reply #120 on: December 31, 2020, 11:45:41 PM »
Rohan, can you put some sort of dye in there that will leave traces of it's presence as it leaks out?  Paint would be a big mess to clean up, but some very thin viscosity dye or chemical should leave a trace where it made contact with any surface. 
Retired, on the downhill slide. . . . . . . . still feels like going uphill!

MikeScoot

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Re: #7 joins the fleet
« Reply #121 on: January 01, 2021, 01:58:41 AM »
Happy New Year, folks.

I'm sure you have thought of it, Rohan, but is there a possibility that the gaskets themselves are the cause of the trouble? You could try tightening it up very slightly without them - using a consistent thin bead of silicone instead - and see if the leak/s persist.

Anyway, I'm sure you have your own list of things to check.

Good luck with it and very confident you'll put your finger on the cause soon.

In the meantime, Happy New Year, again :-)
Luther had his dream,
But I've got my Vision.
His got him into strife,
Mine just takes me fishin'.

Prophet Of Doom

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Re: #7 joins the fleet
« Reply #122 on: January 09, 2021, 07:28:18 AM »
is there a possibility that the gaskets themselves are the cause of the trouble? You could try tightening it up very slightly without them - using a consistent thin bead of silicone instead - and see if the leak/s persist.
The tolerance for head surface flatness is listed as 0.03mm.  I've lapped the surfaces on a 0.001mm certified surface plate so sure I'm very well inside that. 

To test I coated the surfaces in marking out dye, and a few swipes on 400grit paper sees it all scuffed off nice and evenly.
A precision straight edge and a cigarette paper (remember those?) shows no high points.

Turns out there is a variation of 0.5mm in the thickness of the genuine Yamaha gaskets !!! WTF  (Good call Mike)
The metal rings (which do not compress much) are thicker than the compressible part.  No way that's ever going to seal up without some help.

I'll try a good dose of spray copper on the stock gaskets, but I doubt that will bridge a 0.5mm gap.  Alternate plan will be to cut some solid copper gaskets.  If you are wondering about the 83 metal gaskets, they are too thin and gave me valve strike.

By the way, the leaks are in the centre of each cylinder, exhaust side.  There's a drilling there for a half stud. Yamaha never did put this half stud in on production bikes but it does make this the thinnest wall, and so more susceptible to leaks.    It's tempting to put a stud in there.
« Last Edit: January 09, 2021, 04:27:32 PM by Prophet Of Doom »

jefferson

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Re: #7 joins the fleet
« Reply #123 on: January 09, 2021, 09:55:55 AM »
If you have the 83 cylinders then you could use the 83 head gaskets. The 83 cylinders were taller.

Prophet Of Doom

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Re: #7 joins the fleet
« Reply #124 on: January 11, 2021, 05:20:19 AM »
If you have the 83 cylinders then you could use the 83 head gaskets. The 83 cylinders were taller.
I don't have any 83 cylinders.  83s are so rare in NZ as to be practically non-existent.  I'm surprised that the 83 gasket gave valve strike - I didn't think the tolerances were that tight, but there you have it.

Before I went cutting a copper gasket, I thought Iíd try some copper gasket spray on the thick, (but wobbly) Yamaha gaskets.
Did two coats, fitted and let it set up overnight before testing.  I also added a M8 half stud.
Itís happily holding 2 bar of air pressure (29 PSI)  The rad cap blows at 13 PSI so that should be sufficient assuming itís not affected by the heat.

Iím calling it job done, and Iíll bolt the engine back in tomorrow.
« Last Edit: January 11, 2021, 05:26:59 AM by Prophet Of Doom »

kevin g

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Re: #7 joins the fleet
« Reply #125 on: January 12, 2021, 08:33:01 PM »
Mr. Doom, your engine sure looks nice.  You should come and clean mine up in your spare time.

Prophet Of Doom

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Re: #7 joins the fleet
« Reply #126 on: January 14, 2021, 04:24:40 AM »
Mr. Doom, your engine sure looks nice.  You should come and clean mine up in your spare time.
Sure.  No problem
So far my bike has taken about 950 hours - a mere $95,000 worth at $100/hr

Will that be cash or Paypal Kevin?

kevin g

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Re: #7 joins the fleet
« Reply #127 on: January 14, 2021, 08:20:25 PM »
I spent that kind of time on a 1998 R100RS - complete rejuvenation.  Then I decided I liked my modern BMWs better so I sold it.

Prophet Of Doom

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Re: #7 joins the fleet
« Reply #128 on: January 16, 2021, 06:55:03 AM »
Wow, Minty.
Clearly you don't need any help with polishing.  Nicely done Kevin

kevin g

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Re: #7 joins the fleet
« Reply #129 on: January 17, 2021, 07:06:52 PM »
Thanks, I did the paint myself as well.  It is Alpine White with a little blue pearl in it.  The checkers are painted, not a sticker.  The masking was time consuming to say the least.