375 liner enough meat?

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Oli Hulme
Posts: 17
Joined: 15 Apr 2021 11:46
Location: Burnham on Sea

375 liner enough meat?

Post by Oli Hulme »

I've just dropped my barrels off at a local top notch engineering shop, and the expert there looked concerned that the liners might not have enough meat on them to take out to 64mm at the bottom to fit replacement 375 pistons. Is that possible? Or should there be some part of the boring out process that I'm not aware of?

I'm only going to 375 because I can't find any O/S pistons or top end gaskets for 350 barrels.

Ta!
BumbleBee
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Joined: 13 Jun 2017 21:10
Location: Reading

Re: 375 liner enough meat?

Post by BumbleBee »

Usual for the 64mm bore to leave pretty much a knife edge at the bottom of the liner, in my experience anyway.

G&A
MickeyMoto
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Re: 375 liner enough meat?

Post by MickeyMoto »

I know you have the 375 pistons now, but if the original pistons were ok then new rings and new liners would have been an an option.

The lack of head gaskets is concerning, too.
harrymuffin
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Location: west midlands

Re: 375 liner enough meat?

Post by harrymuffin »

Why not anneal the used ones? That's what you do with engines that have copper head gaskets, you can do the same with aluminium ones too!
Oli Hulme
Posts: 17
Joined: 15 Apr 2021 11:46
Location: Burnham on Sea

Re: 375 liner enough meat?

Post by Oli Hulme »

To my enormous surprise and delight, the shop has measured and honed the bores and despite there being 38k miles on it, the wear is minimal, so I can use the old pistons with new rings.
Now to solve the head gasket issue... I'll anneal the old ones, but does anyone know if I can use composite ones?

Cheers all
harrymuffin
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Re: 375 liner enough meat?

Post by harrymuffin »

Composite ones were used in the early days and necessitated continual retorqueing, hence the probable adoption of sold aluminium ones. Although not really necessary, some people use a smear of Wellseal when putting the lids on. Just give the heads a retorque after perhaps 250 -500 miles.
George 350
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Re: 375 liner enough meat?

Post by George 350 »

I must say I preferred the composite ones - no oil leaks for a start. Alloy ones I am sure were a major production cost reduction for Morini.
Aluminium annealing can be done at home. Unlike copper, it doesn't need to get too hot. Rub a bar of soap on the surface, heat the gasket up and when the soap goes brown it is at the correct temperature. Try and apply heat as evenly as possible.
Allow to cool naturally and fit.
As Harry says, some wellseal or a thin smear of instant gasket around the pushrod tunnel area on the head and all over the base ones is worthwhile to keep the oil in.
(Original Morini factory coated both sides of the alloy head and base gaskets all over with a dark red silicon sealant. No idea what that was though. Looked same colour as red hermetite but was definately silicon.)
Enjoy the rebuild as there is light at the end of the tunnel now .
(Unless CEV made tunnel lights!)
Regards, George
George
350 sport 1978, 350 Strada 1978
650 Norton 1967, 650 Kawasaki 1977 and 650 Enfield 2019
Oli Hulme
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Re: 375 liner enough meat?

Post by Oli Hulme »

Thanks chaps!
EVguru
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Re: 375 liner enough meat?

Post by EVguru »

The original sealant as listed in the "Blue Book" is Arexons Motosil D. It is available in the UK, you may find it stocked by competition Yoyo specialists (it's used to fil Yoyos to damp vibrations apparently).

Much eaier to find is Theebond 1215, as listed in the Cagiva era engine manual. I use a bead of about 1mm, which results in just a small amount appearing at the edge of the cases/gasket when torqued. It's very oil tight, but quite easy to break the bond when dismantling.

For annealing, I prefer the "Sharpie" method. Scriible on the gasket with a sharpie marker and heat until it fades. This also works for degrading old sealant (Threebond or Arexons) to make it easy to remove.

There's a seller on ebay.it who's been listing NOS OEM Aluminium gaskets for 250,350 & 500. It might be worth an enquiry to www.centaoro-srl.com. I have some of their Aluminium base and head gaskets and they're listed in their current catalogue.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
mbmm350s
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Location: Berkshire UK

Re: 375 liner enough meat?

Post by mbmm350s »

What are the thoughts on retorquing when using aluminium gaskets. Last rebuild I haven't bothered @6K miles no problems, a previous and different engine rebuild I slackened and retorqued as per blue book, and some time later one base gasket started weeping.
In both cases new gaskets were used.

In a previous question, to use the composite gaskets there must be a machined step at the top of the liner to accommodate the fire ring.
Cheers
Mark
EVguru
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Re: 375 liner enough meat?

Post by EVguru »

Did you oil the threads?
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
mbmm350s
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Location: Berkshire UK

Re: 375 liner enough meat?

Post by mbmm350s »

Hi Paul,
yes I did oil them
I think its having to slacken the nuts off enough to oil the threads
and then something gets disturbed? co-incidence may be? Something to do with the exhaust,
as I didn't slacken that off?

I also I had the same when heads are taken off but not the barrels
that base gasket leaks afterwards.

Mark
EVguru
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Re: 375 liner enough meat?

Post by EVguru »

Never had that problem with Threebond 1215. It's pretty strong, but not so strong that pulling things apart becomes a problem.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
mbmm350s
Posts: 666
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Location: Reading UK
Location: Berkshire UK

Re: 375 liner enough meat?

Post by mbmm350s »

Hi Paul,

The base gaskets leaked after heads removed to fix exhaust port threads.
I couldn't say what gasket sealant was used, one was likely original factory.
The other I cannot remember, it was a long time a go!
I think its probably better to re do the base gaskets if the heads are completely removed?

The one that leaked after retorquing, I don't know what sealant was used,
but on this bike the exhaust was a fight, and I think slackening the head nuts caused movement.
turned out to be a bent rear footrest hanger which was causing the misalignment.

Cheers
Mark
3potjohn
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Location: Devon

Re: 375 liner enough meat?

Post by 3potjohn »

I too am a fan of Threebond, used sparingly. I even used it to fix dodgy plumbing. Harrumph!
Try doing that with red Hermetite.
Do the studs ever pull out in the pleasing way that they can on old Beemers?
John
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