56 G80S blown head gasket

56G80S · Post by **56G80S** » Thu May 31, 2012 4:43 pm

Separate element of the same topic, the exhaust valve and guide were shot, and I had some in my box of new bits.

Rather than fit myself, as the seat would probably need re-cutting took it to a local automotive machine shop, carefully explained about the circlip, driving out into the head and the oilways to line up.

Rang to see if it was ready and told that the new guide and old didn't match. Drive the 10 miles in and after some exploration realised that the inlet guide had been removed, not the exhaust - although I'd taken the guide pre-cooled and in a bag marked ex. guide (in vacuum flask to keep cool). Apparently, although the notes on what to do were also in the exhaust guide, they were thrown by the carb. studs and thought that was the fixing for the exhaust.

On way home and get a call that they'd removed the exhaust guide it was still different from the one I'd taken in (see photo posted in post war singles parts - 56 G80S valve guides).

Go back and reclaim the lot and will refit the in guide (which I had originally put in). But the two ex guides are different in length and more importantly the location of the oilway relative to the circlip ( I have three new ones of these).

I must be a complete idiot, particularly as it's clear (because I was offered the loan of the stepped steel drift) that the guides had been thumped out of a cold head.

I'm not a happy bunny, but would really welcome any views about the two ex guides. In the meantime I'll be measuring up the position of the oilway in the head and seeing if the "new" guide mates up with it.

Just checked the parts list and the new guide is stamped G485 - which is what is listed in JSL lists matched against the part number 022208 and 022208 is also what's listed in my 1956 parts list. Ironically (although the parts list isn't always a good indication)the illustration has the same "relieved" opening for the oilway that the old guide has and G485 that I have doesn't!

The new valve is stamped "V56 MADE IN ENGLAND".

Johnny BEdited by - 56G80S on 31 May 2012 3:44:45 PMEdited by - 56G80S on 31 May 2012 3:59:32 PM

itma · Post by **itma** » Thu May 31, 2012 5:08 pm

Automotive machine shops are not always the best places for bike parts.
why did you not do it yourself? its very simple.

56G80S · Post by **56G80S** » Thu May 31, 2012 7:37 pm

Yes. it's simple. I put in the current inlet valve guide and by good fortune it didn't need the seat recutting and it's fine.

Now have no bench, vice, pillar drill or space. Matchless only fits the shed with less than 6" to spare at either end and is supported by axle stands under the footrests as no room to get it on centre stand. I have to climb over to get from one side to the other. Also thought it would save a bit of time, but completely wrong there.

Guide aperture in head - head to centre of oilway 0.26”; to top edge of oilway 0.22”; bottom edge of oilway 0.36

Old guide - circlip groove to centre of oilway 0.28”; top of oilway 0.15”; bottom of oilway 0.44”; circlip to combustion chamber end 1.56”

G485 guide – circlip groove to centre of oilway 0.5”; to top edge of oilway 0.45”; width of oilway 0.1”; circlip to combustion chamber end 1.92”

Plan to drill the new guide and flare the entrance as per the old guide, only concern is the differing length (OD same for old inlet, old ex and new ex and so is height above circlip).

Will use friends pillar drill, but already lean on his good nature too much! And not in same village.

Johnny BEdited by - 56G80S on 31 May 2012 6:38:14 PMEdited by - 56G80S on 31 May 2012 6:43:23 PM

itma · Post by **itma** » Fri Jun 01, 2012 12:04 am

your problem there me old mate is that is a piss poor guide, I hope it wasn't from the spares scheme?

lack of a countersink around the oil hole is bad, its there for a reason, the excess length can be turned off, if you are really stuck, drill an oil hole in the right place on the other side of the guide.
Also worth, on a bum part like this, checking that the centre hole for the valve stem is concentric to the outside, if not although you get the seat cut true it will be flubbered the next time.

You rarely needed to recut seats if fitting a genuine guide.

also the circlip groove looks narrower than on the others?Edited by - itma on 31 May 2012 11:06:14 PM

56G80S · Post by **56G80S** » Fri Jun 01, 2012 9:46 am

It's so long ago that I bought it that I don't remember, but at that time I usually only bought from the spares scheme.

As always, your advice is valued and your observation about the circlip groove is spot on, I only noticed that after I'd posted. I'd really wanted to get this sorted before the MoT ran out (Thursday next week). I'm away from Wednesday through to Saturday night.

It's insured and taxed (!) for the next year but if the MoT runs out I believe they'll be on to me for something or other, probably have to SORN. I think I'll get a correct guide and just settle for the delay.

Have measured up the barrel to head gap where the gasket sits and it's 33 thou (highest) between the pushrod tubes and 28 thou (lowest) just to the drive side of inlet port. New gasket 38 thou and old used ones 28 - 30 thou. So only 5 thou "pinch" between the pushrod tubes. Based on head on with no tubes in place of course. So it looks like I could be 3 - 5 thou short once head fully bedded in.

By the by I've noticed that there's a 2 stamped on the head in front of the spark plug hole on the fin; never noticed it before.

I feel like an idiot. I think it's old age creeping in.

Johnny BEdited by - 56G80S on 02 Jun 2012 12:49:05 AM

bigwol · Post by **bigwol** » Fri Jun 01, 2012 10:53 am

As long as you have Insurance if it's taxed you should have no problems. New requirement is continuance Ins for taxed vehicle or Sorn. As for the Mot as long as it's not used on the road without one you'll be fine. And come Nov 18th wont need one of those either

56G80S · Post by **56G80S** » Fri Jun 01, 2012 12:34 pm

Thanks for that.

Johnny B