R65 cylinder heads. Looking for identification

[georgesgiralt]

Hello guys,
I plan to rebuild my engine totally. As it is my sole means of transportation, I would like to make the rebuild as fast as possible.
So I bought a pair of cylinder heads to have them totally rebuild by someone and use them as parts for my "new" engine.
Alas the seller was not keen on BMW bikes and send me two different ones.
Could you please look at the pictures and tell me which are for my 1982 Nikasil R65 ?
Thanks for your help !
P.S. : the one or both would be on sale or exchanged for the correct one ....

[Bob_Roller]

The only thing I can tell from the pictures, is that both heads have the port for air injection, for exhaust emissions control .
That started in the '81 model year bikes  for North American market .
Bikes made 09/80 and later .
Nikasil cylinders were introduced at that time .
No idea about European model bikes .

[Tony Smith]

Agree re the airports meaning post 1981 vintage for both.  The one in the RHS photo has R65 embossed on it.

What does the LHS one have?

[georgesgiralt]

The same R65 marking.

[tiggum]

Note also the consecutive model numbers on the bottom of the fin

[Tony Smith]

I'd also make the point that the cylinder heads and barrels are entirely interchangeable - my own R65 has late model heads with Iron bore barrels.

The differences between the two are valve size, valve seat material and a trivial different in deck height of the pistons (late model are 1mm or so taller for higher compression)

[tiggum]

OOPS  (Pushed "send" too quickly)  They appear to be a matched pair, one for each side, so are you certain that one is wrong?

[Bob_Roller]

tiggujm, you can correct mistakes in your post, if you look at the black header, select update session, it will prompt you to put your password in, then select post tools at the upper left side of the posting, you can then edit your post .

[georgesgiralt]

Yes, they are for different bikes. Valve seats are not the same diameter and one has a squish band, the other not.

[mrclubike]

Here is a picture of my heads
They are from a US spec R65 build date 11-81
I have Nickasil cyl
They look like your head in the lower picture
My guess is either one would work if they are a  matched pair but I would want the ones with the larger valves 

It looks like the Head in the top picture has smaller valves
I wonder if it is off of a R45 or the derated R65

[Tony Smith]

Interestingly Mrclubike's head has the same numbers cast on it as the one on the left of georgesgiralt's two photos.

Further, if you actually ever view the deck height of an r65 piston in its barrel you will see that the machined area is not so much "squish area' (that would be the entire circumference of the head, less the area occupied by the top of the barrel, it is in fact an amount machined to increase the volume of the combustion chamber.

Now, here's the thing, without fitting the cylinder up with valves fitted and dropping alcohol into the spark plug hole with a pipette to actually compare the combustion chamber volume, you don't know that they are not in fact equal and simply the product of different casting plants/batches.

Actually you can simply smear petroleum jelly over a sheet of glass and then put the head on it and fill with a measured quantity of alcohol if all you need to do is compare two heads.

Below is a photo of an R45 cylinder head - it simply explodes the theory that either of  georgesgiralt's heads come from an r45  as quite simply R45 cylinder heads have an embossed 'R45" casting mark and a different part number.

I only know of one change of valve size for the R65 and that occurred contemporaneously with the change from iron bores to Nickasil bores.

Looking at the photos I cannot convince myself that there is any difference in the valve seat diameters (measured at the throat of the seat and not the out circumference), but I could be persuaded by actual measurement.

If these heads were mine I would measure the combustion chamber volume and see by how much (if anything) they are different.

If they are different, then I'd investigate the cost of making them equal (assuming that, as I suspect, the valves are the same size) as part of the general rehab process of fitting new guides (or k-lining the existing ones), having the gasket face skimmed true and having new valves fitted up. and if neither of the exhaust valve seats have the "famous" scribed line

[Tony Smith]

continued - (premature emailiation) line around their circumference, I'd be having new seats fitted anyway.

You may find that the cost of equalising the two heads (if required) is less than the cost of buying another head.

That said, there are places around the globe where there are more BMW wreckers than the North-Eastern bit of Australia and it may be that if you go to one of those wreckers they will sell you a pair that are a 100% match for a small premium on top of taking yours as exchange.

I did go through this with my own heads, only to discover that in addition to having been "flowed", they had larger, non-bmw valves fitted, along with non-bmw valve seats which my machine shop was able to match with good quality replacements from Intervalve. What they were not able to tell me was whether or not my valve seats were suitable for unleaded fuel - but around 8,000 miles on the clock suggests that they probably are.

I guess what I'm saying in a nutshell is that without knowing the standard measurements and factoring in that you can't know what has been done to components in their 35 to 40 year journey into your hands, so you have to measure and compare.

My last comment, I may be wrong but I have always understood the de-rating of the R65's horsepower for certain markets was achieved by restrictors in the inlet tract and minor jetting changes. I think that this is true as anything else would have simply cost BMW too much on a per-unit basis for it to be worth their while to do as changing things like cams, pistons, valves etc. would have given them another product line to support with spares etc. As far as I know only the Japanese have ever enjoyed the product volume to make that work, but for the most part when they bring out a de-rated model (for example for the LAMs (Learner Approved Motorcycle) program in Australia) they use restrictor plates and changes in fueling to do so, and only very rarely do they make other changes between the "learner" and "full strength" models.

[Tony Smith]

By pure chance there is a similar thread in the "airheads downunder" Facebook list.

The back story is that the bike is a 1980 R65 which the owner believes to have been unmolested until he pulled it apart for a full rebuild. His question was in relation to whether or not the valve seats are suitable for unleaded. Whilst I don't like the answer he was given (have the hardness tested) his photo raises an interesting point - look closely and one head has significantly more machining done to it than the other which would support my view that it was done for volume equalisation.

Interestingly Ray Peake, who is sort of an Australian poor mans equivalent to Snowbum said that there was only ever one valve size change for the r65 and that it happened from September 1980.

[georgesgiralt]

Hello
So reading your posts, I though I had to measure the valves seats.
I used a ruler so not a very proper tool for the job.
But, the head without the squish band has smaller valves than the other one.
Size seems to match the 1979 version of the R65 and the 1981 version for the other one.
Given the diameter of the cylinder and the molded figures i can say both are for an R65.
So it seems I've a pre-1981 and a 1981 head. The early models had around 45 PS output and in 1981 they got around 50 PS. What I do not understand is that both heads have the ports for the injection of fresh air in the exhaust. if I'm not mistaken, this came only after 1984 in Europe. So I wonder for what market and what exact model those heads are. Do you know if the post 84 model have the 6 mm stem valves or share the same 8 mm stem as the bigger models ?
Last but not least, it is easy to tell if you have unleaded exhaust valve seats. If OEM, they have two rings in the inner vertical wall.
If I use those heads (or one of them) I would have to change seats as they are either burned or chipped. And the valves guides had been tapped in order to try to remove them ! They did not succeed....because the guides are still in place ;-)

[Tony Smith]

Well measurements do not lie, and as a result of those valve seat measurements - you have a weird head that has the post 1981 air port, but Pre 1981 valves

Go figure that one out!

I guess you are looking for a pair if cylinder heads. A search of eBay international sellers does not have any at reasonable prices and a serious number of sellers attempting pass off R45 heads as being suitable for an r65.