Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Crosshead fitting

I have a new chassis for my 69 4/4 and the existing crosshead is to be repaired.

Is there any guide notes anywhere on jigging the crosshead to the chassis to obtain the correct for and aft alignment?

Thanks in anticipation,
John

Go Mog has something on it

Under which section? I have looked but can't find anything!

Phone Terry at GEE

It was in here
http://www.gomog.com/allmorgan7.html#Upper%20Shock%20Bracket%20Replacement

But seems now not to be. I have at home a print out which I can scan for you but I am in Italy today so will do it Thurs


Please pm me your email. I tske no responsibility for the accuracy of the document

Found it search go mog under cross axle. Exttract below:-

Cross Axle Stay Adjustment
The purpose of the cross-axle stays is to triangulate the cross-axle beams into a rigid structure, and thus prevent flexing during bump and rebound. The cross-axle stays are adjusted so that they are always in tension. Too little tension and the front will sag. Too much tension may snap the stay. Tension in the cross-axle stays should be adjusted before having the front end aligned, and checked after alignment.


1. Place the car on jack stands as shown. The weight of the car should be supported by the two inner stands. The outer stands could be distance measuring blocks.
2. Jack on the outer end of one side SLOWLY. The cross-axle should lift simultaneously from both the inner and outer stands (see sketch).

3. If the cross-axle lifts from the outer stand first, the cross-axle stay is too loose. Care should be taken not to jack the car too far off the stands. 1/2" to 1" should be sufficient. If the outer end is more than 1/4" off of the stand and the inner end has not lifted yet, the stay is much too loose.

4. Tighten the cross-axle stay until the cross-axle lifts off of both stands simultaneously. The cross-axle is properly tensioned. No advantage is to be had by significantly increasing the tension.

5. Repeat the above steps for the other side.

John V6,
Thank you for looking unfortunately this only describes the tensioning of the cross head stays and not the fitting of the complete cross head which is what I am looking for.

Cerealsurfer
Yes Terry would jig my cross head if I took it and the chassis to him, however its a long way to travel and I would like to do this at home if I can find the correct procedure.

Edgar

The fitting of a cross frame to a chassis is a long and quite involved procedure, it vitally important that you measure everything at least 3 times and drill only once. There are others who know far more than I and I hope they will also chip in. It helps to have a companion around, to help hold measuring tapes etc , and even better if you can find one who has already done the job. This a build critical point in the assembly , so if you are in any doubt at all about this procedure (or your ability to measure accurately and drill correctly) I would strongly recommend that you bite the bullet and get Terry Foxen to do it for you.

I am not an expert on this particular job , although I have done it rather too many times (having a racer means you have to expect a few bumps).

Firstly ensure that the chassis is off the ground and perfectly level both fore and aft and side to side, it really helps if this is done on level ground. Check that the new chassis is indeed "straight" . You should keep measuring every angle and length and distance above ground , at the same point on each side of the chassis. Once you are convinced this is OK, fit the cross frame in by hand , a good first position is with the bottom of the cheeks sitting on the lower chassis rail, and the lower tube as far back as they will go on both sides) and keep in position with 4 G clamps (BTW you are going to need several G clamps for this job)

Now measure from the lower cross tube back to the front spring mounting point on both sides and compare the measurements , adjust to suit, until they are the same (or at worst within 1 mm)
Now measure from the top tubes back to the same rear point, compare and adjust to make them the same.

Also take measurements of the bottom tube to the floor (if level, if not apply a correction) on both sides and try to get this the same.

All of this will get you a to more and more accurate positioning of the cross frame, but you must also consider the castor angle. This is the angle formed by the inclination of the king pin, this was specified as 4 Deg originally , but most cars came out at around 2 (in the days before MMC used jigs) which is too low. You should be aiming for minimum 4 Deg and some recommend 6. Whichever you go for, it is again vital that is the same on both sides. This will involve moving the frame front up and down whilst maintaining the fore and aft position, not easy. It may be easier to build up a suspension between the tubes using the stub axle and king pin but without the spring to show you the king pin and you can actually measure the inclination with a protractor, otherwise you can do it with lots of measurements and use geometry to calculate the appropriate angle.

Hopefully by now you should be getting a more accurate position which you are happier with . Now is the time to go back and recheck all the measurements to ensure that everything is still dead on (and adjust if not, it will probably take you several iterations before being happy with the result) If you do have a companion get him/her to measure exactly the same points that you have and compare the results, you really cannot check this too many times. Now put some additional G clamps in place as the last thing you want is for it all to move while drilling. Obviously you are going to drill the holes reusing the old ones in the cross frame, but try to ensure that the drill is truly at 90 deg to the chassis, you really do not want to be increasing or ovalising the current holes. Use new high tensile bolts with new anti vibration washers and new nuts of the exact correct size (obvious I know but you would be surprised how many folk don't) Once it is in, and installed , again go back to ensure that all your measurements are still identical on both sides and hopefully the job is a good 'un. If not, you now have an issue as to why and how this has happened, and you really do not want to be redrilling the same holes, but hopefully this will not be the case.

I hope others will add something to this, apologies if it sounds repetitive, but it is vital to get this right if you want to car to handle well, even a small error can spoil your fun once the car is completed.

Good luck

Many thanks Andy for your comprehensive reply. I'm a retired engineer with a full complement of tools so hopefully all will go ok. I'm of the measure once , twice, thrice generation before cutting or drilling.

Cheers and best regards.