Questions About Rebuilding Engine

[Crossrodes]

I'm in the process of resolving some oil leaks on my 79 R65.  The leaks I'm addressing now are around the cylinder base and valve tube bases.  When I removed the cylinders etc I notice that in addition to the O ring seals etc there is a silicone based gasket material around the cylinder bases, the cylinder stud bases and the valve tube seals.

My first question is...is it a good idea to add some silicone base gasket material in addition to the O rings and other new seals?

Second question...Assuming the answer to the above question is yes, I have some 700 degree silicone based Permatex RTV gasket material in a tube. Is this good gasket material to use?

[Bob_Roller]

The only place where you don't want a sealant, is around the threaded studs that have the o-rings around it, that is the oil supply for the rocker arm assemblies.

As far as the use of a liquid sealant, none was used during assembly at the factory.

The push rod tube seals, shouldn't need anything more than some engine oil, or a petroleum jelly for re-assembly.

O-rings seal by being compressed, if oil is getting by them, there is metal worn away where the o-ring contacts it.

I personally have not used any in an o-ring application, on a paper gasket, a thin 'skin' of sealant is all that is needed no need to 'gob' it on and have it ooze out when things are assembled and tightened up.

If you do decide to use a sealant, make sure it is an automotive sealant, compatible with oil use.

Just for general information, all rubber seals need some sort of lubricant for assembly, engine seals can use engine oil, or a petroleum jelly .

Brake system seals, use only brake fluid on the seals.

Fuel system seals, use petroleum jelly, or a light oil.

Fork seals, use fork oil.

Anything in the transmission shaft, or final drive, use gear lube.

If fuel system seals swell after taking something apart, they normally don't 'shrink' afterwards, so be prepared to replace them.  

[Crossrodes]

Thanks Bob.  

Interestingly, there was sealant around the studs with the O rings.  Also my valves were somewhat noisier than a friend's R65, even after adjustment.  I will not seal these studs this time...I'll just use the O rings.  It will be interesting to see the result.

Mike

[MrRiden]

I was just reading something that you can have a look at here:
http://www.gunsmoke.com/motorcycling/r100gs/sealant/index.html
and
http://www.gunsmoke.com/motorcycling/r100gs/pushrod_tubes/index.html
Could be that sealant around the studs was restricting oil flow to the rockers. As for choice of sealant, I've been liking Permatex Moto Seal as of late.
rich

[Bob_Roller]

Thanks Bob.  

Interestingly, there was sealant around the studs with the O rings.  Also my valves were somewhat noisier than a friend's R65, even after adjustment.  I will not seal these studs this time...I'll just use the O rings.  It will be interesting to see the result.

Mike

If your valves are adjusted correctly, and they are still noisy, with tension off of the rocker arms, check the side to side play.

Most likely that is the source of the noise, if you do have excessive play, some owners use a pair of large pliers and with the nuts backed off a bit, that hold down the rocker arms, compress or push the 'blocks' that hold the rocker arms in place together, and then torque the nuts to the specified torque.

I have an alternate method, BMW has shims that are used on the later rocker arms to adjust the end play on the rocker arms, I've been told, that they shouldn't be used on the 'old style' rocker arms, but I have used these shims for about 70,000 miles, and no problems yet.

[Crossrodes]

Bob I was just looking at those shims in a parts diagram for my bike.  I don't have ANY shims on my valve train.  When I adjusted the valves last year I was told to use a "C" clamp to tighten the end blocks and that's what I did.  But who knows if I got it right or not.  I'm inclined to get some shims and see if that gives me a consistently correct end play.  

Do you know the procedure for checking the end play clearance and what should the clearance be?

Mike

[nhmaf]

The clearance should be essentially nil - if you can easily get a 3 mil (.003") feeler gauge in there then it is too much.  The shims only come in certain sizes, though.   with bikes up to ~84 or 85 I think, the generally method is to slightly loosen the head nuts that hold the end block for the rockers, and squeeze together, though I also have had success with a few judicious taps with a hammer using a socket whose inner diameter is greater than the end of the rocker arm shaft.   I think that BMW changed the way these were machined around 86 (I cannot recall, but someone will correct me) so that the blocks should not be subjected to sideloading as it can damage the studs, and thus the shims came into existence.

I've got my clearance down to somewhere just over .001" and it quieted down significantly - basically the thickness of the film of oil.

To check the amount of end play, put that cylinder at TDC like you would for adjusting the valve lash/clearance.  Push on the rocker arm just enough so that it isn't dragging on the end of the valve or the pushrod, and see if it moves up and down along  its shaft.   If you can fit more than a .003" feel gauge in between the rocker arm and either the upper or lower end block while sliding the rocker up and down, then the clearance may be excessive.  It generally doesn't do any real harm, but can create more noise.

As far as valve lash/clearance goes, the generally accepted measure is .004"/.008" intake/exhaust, though I tend to set mine at .005"/.010" - they are slightly "tappier", but I think the extra clearance allows more heat to dissipate from the exhaust valve/seat, to head off valve deformation (until I am ready to send the heads off for new valve seats).

[Bob_Roller]

I have not seen an official procedure on adding the shims, I just took a measurement using feeler gauges, and divided it in half, and then put that amount of shims on each side of the rocker arm.

I left about .003 in. (.08 mm) cold clearance on the rocker arm clearance, and have not had a problem yet.

What cold clearance are you setting your valves to ?

[Crossrodes]

The last time I set them I used the clearances in the Clymer manual....004/.008"  (In/Ex).

Mike

[Justin B.]

Mike, they are off on a tangent about rocker arm end-float...