Author Topic: Cylinder base gasket 'blown out'.  (Read 2198 times)

Offline t20racerman

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Cylinder base gasket 'blown out'.
« on: 23.07. 2011 17:40 »
Hi all

Been out for a thrash on my newly rebuilt A10 and the cylinder base gasket has been blown out the front of the barrels! All across the front it is sticking out and has clearly been under pressure as it is ripped in half where one of the studs was.
I was really surprised at this as the gasket was quite a thick one and was securely fixed to the crankcases with gasket glue. I used high quality 'Yamie bond' (Yamaha recommended crancase sealant for my TZ350) and tightened the barrels down (without pistons) after fitting the gasket to ensure it sealed correctly. I then rebuilt the top end and greased the barrel gasket joint. All the barrel bolts were tight and were retightened after 50 and 150 miles.

The engine breather is assembled correctly and there is no oil coming out of there. The rocker cover barely leaks at all and so I'm not convinced there is a pressure problem.

Any ideas as to why this happened?
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online bsa-bill

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Re: Cylinder base gasket 'blown out'.
« Reply #1 on: 23.07. 2011 18:35 »
Hi t20racerman
Can't offer much in the way of an explanation but enquiring minds might want to know why fit barrels without pistons
Presumably you take barrels of again to fit pistons or you have a cousin called Merlin.

obvious question is going to be are the cranckase halves a true pair
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline t20racerman

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Re: Cylinder base gasket 'blown out'.
« Reply #2 on: 23.07. 2011 19:26 »
Cases are indeed a matched pair and this never happened to me before in 30,000 + miles!
I fitted the barrels without pistons to ensure that the gasket glue sealed with the barrels in place and under pressure - the idea being that this would help make the 'perfect' joint!

I then rebuilt the next day WITH pistons in place.  *smile*
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Offline t20racerman

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Re: Cylinder base gasket 'blown out'.
« Reply #3 on: 23.07. 2011 19:38 »
Just had a thought.....

Yammie bond is designed primarily for gasketless joints. The gasket that has blown out seems completely clear of bonding. Maybe it didn't bond? Still doesn't explain why it blew out though...
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online bsa-bill

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Re: Cylinder base gasket 'blown out'.
« Reply #4 on: 23.07. 2011 19:50 »
Not sure I agree with your method, probably weakened the gasket when removing the barrels.
I'm using loctite 5910 these days basically a black silicon ( on both sides of a gasket) but it does seem to lift ok when removing and sets like rubber (not hard)
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline fido

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Re: Cylinder base gasket 'blown out'.
« Reply #5 on: 23.07. 2011 21:27 »
Yes, taking the barrels off to fit the pistons means you were in effect using an old gasket which could have compressed slightly differently the second time is the barrels didn't sit in the exact same place as before. I wonder if the crankcase face is flat?

Online muskrat

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Re: Cylinder base gasket 'blown out'.
« Reply #6 on: 23.07. 2011 21:35 »
I'm with Bill & Fido on that one t20.
I also think your right about the yammie bond being for metal to metal joints. I have used kawasakibond (same stuff) for the crankcase joint with no problems, but it was no good on timing side or rockerbox gaskets. I use permatex #3 for most gaskets.
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Online orabanda

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Re: Cylinder base gasket 'blown out'.
« Reply #7 on: 24.07. 2011 01:54 »
Is the crankcase breather working correctly? (timed correctly, hole not blocked?)

richard

Offline t20racerman

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Re: Cylinder base gasket 'blown out'.
« Reply #8 on: 24.07. 2011 11:06 »
I'll re check the breather Richard but it does all look fine.

I'm feeling more and more strongly that the Yammie bond had no adhesion whatsoever on the gasket so I'll try something else next time. Still puzzled as to why a 3-4 inch strip of gasket should blow out though. Looks like the same has happening on the rear LH side too! I'll strip it down and report back but I have had one idea as to a possible problem - I fitted new base studs to the crankcases.... I wonder if the nuts were tightening down on to the base of the thread, rather than to the barrel itself? They were the correct studs for my thick flange barrels but it is certainly worth checking I feel. They look fine, but I can't really tell until the cylinders are lifted off. I had a similar problem on my T20 racer where the head gasket kept blowing, and I couldn't see why. It turned out that although the heads were tightening down, the last little nip up was pressing the head bolt studs down to the end of the thread, rather than tight against head!

Anyway, thanks for your thoughts - now time to get the spanners out :-)
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online Triton Thrasher

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Re: Cylinder base gasket 'blown out'.
« Reply #9 on: 24.07. 2011 12:53 »
Cylinder base studs commonly loosen after a few miles.

Also- you can get a buildup of old Hermetite around where the studs go into the crankcase, holding the barrel up from mating properly with the crankcase face.

Offline t20racerman

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Re: Cylinder base gasket 'blown out'
« Reply #10 on: 24.07. 2011 20:46 »
All stripped and now I really am puzzled! It took me ages to lift the barrels as they were absolutely solidly stuck down to most of the gasket. The yammie bond on the bottom had bonded to the cases in most a, but the front is completely blown out, and the bottom LH side was on the way out. I've attached pics and you can see what I mean. Oddly, the LH side bit that was partly out was stuck down solid to the cases and I ripped a bit trying to lift it off as you can see in the pic.
Cases are a matched pair, surface was dressed and made flat before fitting new studs, studs were correct length, casings hadn't lifted around the studs (I'd slightly countersunk them before fitting), gasket glue had bonded, most of gasket absolutely solid, base of barrels seem flat...... ???

all I can do is rebuild I suppose :-)
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online bsa-bill

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Re: Cylinder base gasket 'blown out'.
« Reply #11 on: 24.07. 2011 21:02 »
Hi t20racerman
Photos are all 0KB (empty file)
With out seeing the photos I'm assuming some Yamabond stuck ,some not then refitting is like using an old broken gasket.
if you clean it all off, put a smear of goo all round then the gasket, next barrels and fasten down I'll be surprised if it's any more bother.
If you wan to fit gaskets that can be removed and re-used the plan most used is goo on one side of the gasket, slight smear of grease or nothing on the other side, then the gasket will stick to one face and not the other.

All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline t20racerman

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Re: Cylinder base gasket 'blown out'.
« Reply #12 on: 25.07. 2011 12:52 »
Hi t20racerman
Photos are all 0KB (empty file)
With out seeing the photos I'm assuming some Yamabond stuck ,some not then refitting is like using an old broken gasket.
if you clean it all off, put a smear of goo all round then the gasket, next barrels and fasten down I'll be surprised if it's any more bother.
If you wan to fit gaskets that can be removed and re-used the plan most used is goo on one side of the gasket, slight smear of grease or nothing on the other side, then the gasket will stick to one face and not the other.

Photos there now (I hope)
I did use goo on one side and a light greasing on the top surface. I`ll try again and see what happens....  *smile*
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online bsa-bill

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Re: Cylinder base gasket 'blown out'.
« Reply #13 on: 25.07. 2011 13:19 »
the front section hat has blown out has what appears to be bit's of something on the top of it, is this stuff that's got on it after you've taken it off,
Also there is what looks like oil on the cranckase joint is it oil or is that the Yamabond, if it's Yamabond it looks like some stuff I used once, didn't like it as it set hard
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

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Re: Cylinder base gasket 'blown out'.
« Reply #14 on: 25.07. 2011 14:18 »
Bill, Yambond is silver colour and similar to hylomar not hard setting. So with the soft goo not sticking to the gasket on one side and grease on the other and compression of the gasket the crankcase pressure has blown it out.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7