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+--- Thread: Engine mounting torque (/showthread.php?tid=9348)
Engine mounting torque - Nick Mayne - 06-05-2024
Many of you will be familiar with the engine 4 bolt mounting on the chassis which uses 4 large diameter rubbers between the engine lugs and the chassis, smaller diameter rubbers and washers on the top with rubber tubes around the bolts through the engine lugs. This results in no metallic contact between the engine and chassis thus giving some compliance. The question is how tight should I fix the four bolts so as to retain them ok but not lose the compliance? I tried 15lb.ft but the washers under the top bolt heads sunk into the top rubbers. I have found some washers larger diameter than I used so that may overcome the 'sinking' but the torque question remains. Maybe there were special washers originally?
The front two bolts are tapped into the chassis but the rear two go through to locknuts underneath. Because the chassis holes for the rear two are nearer the side of the channel than they should be, a socket will not fit on underneath so molegrips there and socket on top! Possibly I could find a very thin wall socket.
Of course one cannot use a socket for the rear bolt head which is underneath the starter motor housing so I have to use a very small spanner with mole grips underneath!!
Nevertheless the main question remains as to how tight to try and fix those bolts? Making a judgement is not so good in this case.
Your views appreciated, Nick
RE: Engine mounting torque - Reckless Rat - 06-05-2024
Not very tight is the answer. Just so the upper doughnut begins to compress.
You can resolve the rear mountings problem by replacing the mounting bolts with one with a 'D'shaped washer welded on the head, which will prevent it from turning in the chassis rail. It makes assembly easier as you then only need access from above. Simplify access to the rear RH mounting by removing the starter motor, or by a combination of socket/universal coupling and long extension.
RE: Engine mounting torque - John Cornforth - 06-05-2024
Hi
I did this job a few weeks ago. Mine are fixed with castellated nuts and split pins, so I just did them up until I could get a split pin through. Sounds easy but it's a real faff as impossible to see without a mirror. At this setting the uppermost rubbers are squashed out to a slight barrel shape, but not excessively. My upper washers are the same diameter as the uncompressed top rubbers.
Nylocs would be another possibility if you don't mind their appearance
I don't think there is supposed to be nearly as much vibrational movement in these mounts as modern types give, maybe only a millimetre or so. Tugging the engine by hand gives no noticable movement. Still a step up from solid mounts though !
RE: Engine mounting torque - Chris KC - 06-05-2024
Likewise, not very tight - just enough to stop the engine flopping about or separating from the frame on speed bumps.
I use nylocs underneath - they may loosen but they're unlikely to drop off completely.
I habitually leave one of the rear fixings distinctly loose so it's effectively a 3-point mounting.
RE: Engine mounting torque - AustinWood - 06-05-2024
I use nylock nuts on the bolts at the back and we have bolts into blind holes at the front. Being 1929 there is no rubber so I don't do them up tight. Doesn't seem to make much difference if they are loose.
RE: Engine mounting torque - goodwoodweirdo - 10-05-2024
Does anyone watch Shed racing by Ivan Dutton on youtube, after cracking various parts engine, gearbox and rads due to chassis flex he has now installed springs - great to watch ...
RE: Engine mounting torque - Parazine - 10-05-2024
I use an ordinary nut, brazed onto another on rear engine mountings to make them easier to do up and undo, a la 750 Companion, page 111. They're secured with a plain washer and split washer.
This applies to the solid mounted engine, early chassis which seems to rely on the stiffening action of the engine to brace the chassis.
Later, rubber mounted varieties usually have a split pinned bolt at the back, stud at the front or a substitute nylock as they are not done up very tight at all.
RE: Engine mounting torque - goodwoodweirdo - 10-05-2024
To minimize any chassis flex why not make a plate that runs from both sides just back from the nose ? wouldn't that provide sufficient stiffness ? could be welded or bolted on and would ultimately relive the engine and its mounts ?
RE: Engine mounting torque - Nick Mayne - 12-05-2024
Thank you all; it has been an interesting discussion. I had to get some larger washers to fully cover the top rubbers. Possibly the originals got lost at some time. I will tighten the bolts to just starting to balloon the top rubbers. The rear bolts have locknuts form David Cockrane. The front are blind into the chassis so I have to hope the 'ballooning' and friction will stop them coming undone.
RE: Engine mounting torque - AustinWood - 12-05-2024
I find the fronts do come loose. It doesn't seem to make any difference. This is a 1929 solid mounted engine.
As a general rule Austin nuts and bolts should be done up firmly using a spanner the size provided in the original toolkit. ie Not very tight. No torque figures were published.