Gasket quality...

So, my T140 sprang a leak from the exhaust rocker box gasket. I wasn’t too worried as I wanted to get inside it soon anyway. One reason being that it’s a bit of an oil burner too.

The leak was due to the fact that the rocker box gaskets were super brittle, they just snapped. In the area of the leak, the gasket had basically crushed and powdered.

The oil burning turned out to be similar, oil was making its way down the rocker box through studs and instead of being sealed by the head gasket, oil was making its way into the combustion chamber. Again, the composite head gasket material around this area was crushed and uneven and in no way in a condition that you‘d expect to seal.

The engine was rebuild when I bought the bike a year and a half ago, the builder knows late Triumphs very well... but... he’s a bit of a Wassell fan. I suspect the gaskets might be Wassell, and being someone who is not a Wassell fan, I suspect this might be the issue.

So... are there any known good or bad gasket suppliers or manufacturers out there?

Harris is as good as we’ve got to OEM, they’d be my normal default choice. Any other suggestions ?

Did you look at the Andover selection?

https://andover-norton.co.uk/en/shop-details/22216/valve-cover-gasket-750

When I have a tough sealing problem, I usually turn to synthetic cork, and find it stops the leak.

I don't know how T140 rocker box differ from Norton, but my Atlas is on its second set of rocker box and rocker spindle gaskets, and no leaks since I changed from the originals.

Slick

texasSlick said:

When I have a tough sealing problem, I usually turn to synthetic cork, and find it stops the leak.

I don't know how T140 rocker box differ from Norton, but my Atlas is on its second set of rocker box and rocker spindle gaskets, and no leaks since I changed from the originals.

Slick

Click to expand...

I do want to try the ones from @jseng1 next.

texasSlick said:

When I have a tough sealing problem, I usually turn to synthetic cork, and find it stops the leak.

I don't know how T140 rocker box differ from Norton, but my Atlas is on its second set of rocker box and rocker spindle gaskets, and no leaks since I changed from the originals.

Slick

Click to expand...

The rocker boxes are separate on a Triumph, bolted to the head, with a gasket between them. It’s not the rocker covers I’m referring to...

The rocker boxes can squirm around a little giving gaskets a hard time, hence they were dowelled on later models.

Copper is often used by tuning types, ditto for the head gasket. The OEM gaskets were those grey faced types and worked well.

Perhaps I’ll end up going copper.

If they squirm around then use a stronger glue.

Wire reinforced:

A trick you can try is, after applying the sealer of your choice, to put down a silk thread around the perimeter of the sealing surface, looping the thread around bolt holes. The silk thread prevents the sealer from being squished completely out, and also acts as a "fence" to prevent migration of oil.

PM me your postal address, and I will put 2-3 yards of silk thread in the mail.

Slick

swooshdave said:

If they squirm around then use a stronger glue.

Click to expand...

Perhaps squirming was the wrong word? The rocker boxes can move around, especially at high rpm, especially if the valve springs are stronger than stock. It’s the valve springs acting on the rocker boxes that induces the squirming. Glue won’t help.

L.A.B. said:

Wire reinforced:

TRIUMPH ROCKER BOX BASE GASKET (2) WIRED T120 T140 BONNEVILLE 1971-83 71-2599 W | eBay

THIS SALE IS FOR A PAIR OF O.E. QUALITY WIRE REINFORCED TRIUMPH ROCKER BOX BASE GASKET FOR 650 AND 750 TRIUMPH TWINS FROM 1971 - 83. OE PART NUMBER 71-2599.

www.ebay.co.uk

Click to expand...

They‘re the ones I was looking for LAB, thanks.

Am still considering copper though...

texasSlick said:

A trick you can try is, after applying the sealer of your choice, to put down a silk thread around the perimeter of the sealing surface, looping the thread around bolt holes. The silk thread prevents the sealer from being squished completely out, and also acts as a "fence" to prevent migration of oil.

PM me your postal address, and I will put 2-3 yards of silk thread in the mail.

Slick

Click to expand...

That’s very kind of you Slick, thanks for the offer. I’m in the U.K. though, postage will cost a lot more than the thread !

L.A.B. said:

Wire reinforced:

TRIUMPH ROCKER BOX BASE GASKET (2) WIRED T120 T140 BONNEVILLE 1971-83 71-2599 W | eBay

THIS SALE IS FOR A PAIR OF O.E. QUALITY WIRE REINFORCED TRIUMPH ROCKER BOX BASE GASKET FOR 650 AND 750 TRIUMPH TWINS FROM 1971 - 83. OE PART NUMBER 71-2599.

www.ebay.co.uk

Click to expand...

They‘re the ones I was looking for LAB, thanks.

Am still considering copper though...

I use copper with a very faint smear of Victor Reinz grey silicone on both sides, or alternatively Wellseal. No leaks.

Martyn.

Thanks Martyn.
Are you talking head gasket and rocker box base gaskets?
The more I think about it, the more I’m inclined towards copper for both.

I was meaning rocker box base but I've used copper for the head also. The Harris supplied flame ring head gaskets are fine also, but do require several re torques.

From what I can tell this is what AN uses for the rocker box base gasket. It looks to be the same thing used for cylinder base gaskets.

Matchless said:

I was meaning rocker box base but I've used copper for the head also. The Harris supplied flame ring head gaskets are fine also, but do require several re torques.

Click to expand...

Thanks again Martyn, now, for a bonus point, do you know how thick a Harris head gasket crushes down to?

They start off at 0.065" & crush down to around 0.050" ish (that's British Standard ish) The copper ones I've used have been 0.040" ish.

Thanks again Martyn.