R26 engine a tight fit in frame

[BSA Bob]

I've fitted new rubber mounts to my rebuilt R26 motor & I'm having a lot of trouble fitting it into the frame
The engine fitted easily enough before, though the old mounts were very poor & badly worn.
Is this a recognised problem or is something too tight?

[BSA Bob]

[Taz]

Hi.

Where would the problem arise...at the lower mounting points or at the front?

Kind regards, Ute

[BSA Bob]

Hi Ute
At the moment I'm trying to line up the bottom mounts. I have the rod fitted in the bottom left frame mount & crankcase but am having trouble lining the engine up in the frame. The bottom rubbers protrude a couple of mm from the crankcase & this seems to be stopping the crankcase from lining up.

[Taz]

Hello Bob.

Thanks...the rubbers protruding are meant to be..however, the original setup sees the rubbers on a tube that will connect to the inner flanks of the frame on each side with the bolt only touching the framew and tube, not the rubbers..so the engine would be resting on the rubbers and be able to vibrate happily...check out the BMW document for that...or let me know, I could post am image later on...

So if the tube is missing then the frame might be bent inwards a little, squeezing the rubbers and making putting the engine a tough job..

All the best, Ute

[4Taktix]

Hi Bob,
apart from the rod there's also a support-tube to be fitted, meant to keep the frame tubes on proper distance.
This prevents the mounting rubbers to be squeezed to much by tightening the Nuts.
The inner surface of the mounting blocks has to be flat, there should be no nicks or grooves around the hole.
Probably your lower frame tubes were warped inboards, if there was no support-tube mounted before.
( common ) You can try to widen the frame by spanning the tubes with a car-jack, then fit a scantling
between the tubes until the engine is mounted with the support tube.

Regards,
Sascha

[4Taktix]

... pictures say more than thousand words.
We're talking about tube "C" - to be sticked through the engine, then put the engine with rubbers in between
the frame tubes, then stick the rod "11" through the tube "C".
Hope this helps.

Sascha

[BSA Bob]

Thanks for the replies folks.
I have the support tube fitted, it measures 166.3mm length. It protrudes about 3mm each side of the crankcase. Prior to fitting the engine I tried the tube in the frame, there's about 1mm play between the frame rails like this. The play is easily taken up by hand tightening.
The old rubbers had the protruding lips scraped off, I don't know if this was deliberate or wear.

Bob

[4Taktix]

It protrudes about 3mm each side of the crankcase.

Yes, that sounds just about right. I wonder why your rubbermounts were scraped off then.
It may be, that the tube worked into the square frame blocks a bit on the inside, so you're short of exactly that depth.
If so, then the tube needs to be slightly longer ( ~ crankcase-width + 2 x protruding thickness rubber + notch-depth )
Best way is to fill the notches by welding and reboring, or quick & dirty mount it with proper fit washers.
The rubbers must not be crushed too much, but also the engine must not move sideways on the tube.
Maybe you can find appropriate stock in your DIY-store to make one particularly matching your frame.

Regards,
Sascha

[BSA Bob]

I fitted the engine, but it was a struggle. The frame rails & mounting tube looked OK & as I said before the mounting tube protruded about 3mm either side of the crankcase. But with the mounting rubbers fitted the crankcase assembly was several mm wider then the frame, both front & back mounts. I had to lever the engine in.
But now it's fitted it looks OK, the rubbers don't appear squashed.
A visit to the refrigerator is called for.