A silly question

[(RIP) Tibs]

...from the ministry of silly questions.
I'm trying to put my 1979 R80/7 back together and I'm just a little confused about the barrel base gasket or O ring.
Snowbum says you can tell if it should have an O ring because there'll be a groove for it. Is this a deep groove? There is a slight depression around but it doesn't look like the sort that O rings normally sit in.
Can't find a photo of one anywhere to compare with.
Any help will be handsomely rewarded obviously......
Cheers
Tibs

 

[Kenny]

Some had the large O ring, others didn't !!

Have a look here.....

http://www.realclassic.co.uk/bmw_r80_r100_conversion.html

 

[Rob Farmer]

It's an obvious groove if you have it.

Does your engine look like this - finned timing case and smooth airbox?

or is the timing case smooth like this?

 

[SeanW]

I was wondering exactly the same thing - just been stripping my 1979 80/7 in last couple of weeks, and was nonplussed to find no evidence of either O-ring or base gasket.

(mine has finned timing case...)

 

[SeanW]

also, what brand of sealant works best between barrel and crankcase(yes, have read about care you need to take with sealant near the top studs/o-rings)

 

[Rob Farmer]

Sean i've tried all manner of sealants including the BMW recommended Dri-Bond - They have all "misted" when the engines been hot. The best results have always been to get the mating surfaces spotlessly clean and just use the O rings for the pushrod seals (and base O ring if you have one).

 

[Rob Farmer]

(mine has finned timing case...)

The 1979/80 bikes were a cross over between the heavy and light flywheel bikes. They are my favourite engines, you get the heavy flywheel engine with nikasil lined bores and a points bean can which can be swapped for an electronic beancan.

 

[(RIP) Tibs]

Thanks to all for the various responses.
I've got the finned timing chest, and no obvious groove apart from the ones for the 2 small O rings. I hadn't realised the timing chest was significant, does that mean it's a late 79 model?
Tibs

 

[MikeP]

When rebuilding my mates '79 registered 80/7 some years ago, I found that one cylinder had an o-ring and one didn't.

My assumption is that at some stage a replacement barrel was fitted. Which was the original I have no idea.

Neither had base gaskets when I stripped it but I fitted them as both had been misting. It's not started misting again since the re-build but it has led a more genteel life than it used to.

 

[Rob Farmer]

I hadn't realised the timing chest was significant, does that mean it's a late 79 model?
Tibs

The fined case means it has a single row timing chain instead of the earlier duplex chain. 77 to 81 saw lots of changes in the bikes. the best way of finding out which model/year your bike started out as is to put the vin number into here -->> http://realoem.com/bmw/select.do

BMW's year runs from start of September to the end of August. So a 1980 bike could actually be from September 79.

 

[Rob Farmer]

When rebuilding my mates '79 registered 80/7 some years ago, I found that one cylinder had an o-ring and one didn't.

My assumption is that at some stage a replacement barrel was fitted. Which was the original I have no idea.

You have to be carefull with the piston rings, different rings for different barrels if you get the non nikasil rings in the nikasil barrels or visa versa you end up with a very high wear rate.

 

[(RIP) Tibs]

I must admit I am tempted to fit a gasket. I can't imagine it could do much harm, except maybe reduce the compression ratio a teeny bit. Just relying on hylomar seems a just bit optomistic thirty years down the line.
Tibs

 

[Rob Farmer]

Metal to metal with new o rings on the studs is all that's needed.

 

[(RIP) pastyman]

Ive always used a sealant called "Wellseal" brilliant stuff, can be put on as thin as you like, will not clog like hermatite and the likes. Its quite expensive but coms highly recommended by a lot of engineers.

 

[(RIP) Tibs]

Cheers, I'll have a look for Wellseal, I've not heard of that one before.

Going back to Rob's comments about the ignition: you seem to be suggesting that swapping to the electronic bean can is a good idea. I had hoped to go for a Boyer set up, but decided the cost was too high, so I thought I'd probably stay with points as at least they're very straight forward. (Apart from the fiddle-arse job of adjusting them inside the can!)
Id be interested to hear any further thoughts on the pros and cons of going electronic.
Cheers
Tibs

 

[Beemerboff]

I fitted the basic Boyer unit to my /7 sometime last century.

Didnt cost much, less than the cost replacement points would have been over that time, and it was fit and forget - no replacement , resetting the timing, burnt wrists, etc.

I set it to give full advance at 3500 revs, and I think the bike goes better that way too.

Either Motobins or Motorworks still have the base unit- I don't think you need anything more.

 

[SeanW]

mixed barrels

had a closer look at the barrels at weekend, and guess what - one has the O-ring, and the other one doesn't.

suppose, will just buy the one O-ring for the rebuild!

 

[(RIP) Tibs]

Its not often you can halve your maintenance costs as easily as that!