375 liner enough meat?

[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]

Usual for the 64mm bore to leave pretty much a knife edge at the bottom of the liner, in my experience anyway.
Edit; Just remembered my 370cc cylinders are bored out from something like a 250 2c, which would explain why the liners are like a knife edge.

G&A

[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]

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]

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]

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]

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

[Oli Hulme]

Thanks chaps!

[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.

[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]

Did you oil the threads?

[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]

Never had that problem with Threebond 1215. It's pretty strong, but not so strong that pulling things apart becomes a problem.

[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]

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