Hippo update time.

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canaletto5
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Re: Hippo update time.

Post by canaletto5 »

Not now you won't :oops: :lol:
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Alan H
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Re: Hippo update time.

Post by Alan H »

You gret chick, chick chicken!
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canaletto5
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Re: Hippo update time.

Post by canaletto5 »

I just don't want to be around when Lyn realises it was YOU that made the link between a lovely lady and a clapped out horse ;)
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Alan H
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Re: Hippo update time.

Post by Alan H »

Don't try to
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out of it now mate.
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canaletto5
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Re: Hippo update time.

Post by canaletto5 »

Precisely :lol:
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Alan H
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Re: Hippo update time.

Post by Alan H »

I've explained the situation to her tonight when she got in from the coven, and she really wants to meet you and explain certain things, apparently. :roll:
I suggest you fetch a hard hat and energy shield.
And toilet roll.
Lots of toilet roll.
:)
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Alan H
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Re: Hippo update time.

Post by Alan H »

After 428 miles over the rally weekend, the hippo seems to have settled down somewhat.
As mentioned earlier, after a discussion with John Jenks, we realised that the L barrels had been decked and when Baz measured them last week, they'd had 1mm taken off the bottom.
This seems to mean that the distance from port closing to barrel top is 1mm less than a standard L (which has low ports I believe?), plus 1mm oversize bore gives more volume to start with (253cc per cylinder) and a helluvalot less volume to finish with. The piston/head clearance must have been very close to bugger all. Total engine size now 760cc!
The static pressure was 150psi per cylinder, so what the pressure was when the spark plug did its stuff, heaven knows. Suffice to say, the pressure must have been very close to the limit and caused heavy vibration at anything over about 5500rpm, the once it did 6000 nearly shook my fillings out!
We spoke about this in Ireland and I was going to strip the top off and do some measuring but the head gasket let go on the way to Mike's house a couple of weeks ago, so never got the chance.
Anyway, motorway speed fuel consumption is about 43-45mpg, which is what it was before the barrel swap, but the vibration is much less as is the surging. Power seems to be very similar, and the bike pulls well and seems to be happier to rev freely. 6000rpm through the mid gears when getting onto the A1 on the way home didn't cause any issues anyway - except to those behind who got the benefit of the spanny smoke...........
Hopefully the reliability problems are now sorted and Baz has done good.
We've all learned from this (eventually!) and maybe the knowledge will be useful for others too.
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BAZ
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Re: Hippo update time.

Post by BAZ »

Hopefully, you will stop throwing thing's at me now Alen! Anyway, great weekend and beat the weather somehow thanks for arranging it Pete and Mandy.
teazer
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Re: Hippo update time.

Post by teazer »

150 psi is not surprising with such low exhaust port. It would now be 43.5mm down, so lots of time to build compression after it opens. My ported motor runs 165psi and it is as smooth as a baby's cheek. It should be a low rpm torque monster like that. I would be surprised it it revs though.

What we have seen on multiple GT motors is a serious mismatch between combustion chamber and bore - especially when a head or barrel has been swapped out. That mismatch plus stock 76mm head gaskets are the reason they fail repeatedly. Pull the barrels and head off and see how well/badly they match. Then get a decent head gasket from Cometic and get them made to say 71mm bore or 72 at most. OEM are way larger and that's where they fail.
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Alan H
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Re: Hippo update time.

Post by Alan H »

500 miles on the hippo since the last rebuild and seems to have settled down somewhat.
Hopefully the issues are sorted and we can get down to some reliable biking now. Whistle see.
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