Category: Marcos Modifications

Finally finished setting up the car suspension. It’s still not perfect but its a lot better than it was originally. With the suspension completed I thought is was about time to take the car to a rolling road to get the carb set up correctly. This went fairly well but highlighted a fueling issue above 4000 rpm. If you look at the rolling road print out you will see that the AFR (Air Fuel Ratio) increase from 13.2 to 15 from 4000 to 5500rpm. The ideal being 13.2 for acceleration. There could be 2 reasons for this, one being the mechanical fuel pump can’t deliver fuel quick enough or the main jets are too small. As the carb has the recommended jet size fitted it is most likely caused by the fuel pump. As the rolling road didn’t have the next jet size available we were unable to confirm the exact cause.
My plan now is to fit an electric fuel pump and then I will return for another rolling road session. I will also be taking the next size jets with me just incase the electric fuel pump hasn’t fixed the issue. As for my engine the performance it is spot on at 130BHP which is exactly correct for an early Essex V6 engine fitted with the standard oval port heads. I am tempted to fit an up rated engine but this is defiantly a project for another year as upgrading the rear axle first is more important for me.
One photo below shows how the track rod end is attached to the steering arm. I plan to have a spacer machined to replace the temporary spacers was I’m confident that no further adjustments are required. The other item is a scan of my rolling road session for the Marcos car.

 

 

Spent the last 2 days trying to adjust my cars suspension and it’s still not right. It’s probably a lot closer than it was but its still not as good as it should be. Having completed the bump steer modifications the toe in now only changes by about 2.4mm over the whole suspension travel which is a vast improvement over the 2cm change that I had before I started the modifications.
I only shorten the steering rack by 5cm but it looks like that was slightly too much! The computer model I did can’t have been as accurate as I was expecting as the only way to reduce the bump steer now would be to extend the rack very slightly (Don’t think I will bother as 2.4mm is good enough). Before continuing with the suspension setup tomorrow I have taken the car out for a drive tonight. The handling was defiantly better along the bumpy country roads but the car is still pulling slightly to one side.
I think I lot of the issues I have with the front wheel suspension setup is due to the castor not being equal between the two front wheels. However with the equipment I have this is the one thing I can’t measure so it’s impossible for me to correct. I plan to check the suspension settings again and if everything still looks ok it must be caused by the caster angle being incorrect so I’ll have no choice but take a trip to a garage so they can measure it for me.
If I remember I will also take some photo’s of my front suspension tomorrow and upload them to my web site.

After being away for the last 4 weeks I’ve returned home and I’m ready to complete the suspension modifications to my car. Since I last worked on the car the high angle misalignment rod bearings have arrived. This has enabled me to fit them to the car and measure up what I need to fabricate to be able to connect these to the steering rack. Having now taken the measurements I will now need to wait a few days till the machine shop has time to fabricate them (with a bit of luck they will be ready by Friday). While I’m waiting there is very little I can do to my car however I do plan to visit a fellow Marcos owner on Thursday and give them a hand with their car. If the machine shop does complete the parts by Friday I plan to spend the weekend setting the car suspension and wheel alignment up. I expect this to take some time as when you adjust one setting e.g. ride height it affects other settings such as wheel alignment and camber. I also need to spend some time measuring the bump steer on the car to determine the ideal amount that I need to shim the rod end bearings to minimize the bump steer.

 

It’s 2010 and its been a busy year so far. Since returning to work in the new year this has been the first time I’ve had some time off and been able to work on the car. Today I removed the steering rack from the car and stripped it down so I could shorten it. To achieve this the internal shaft was cut into 2 and a 50mm section was removed from the middle of the shaft. These were then taken to the local machine shop were a lathe was used to drill and tap a 1/2″ UNF thread into the end of each section. These were then joined back together with a 1/2″ unf stud and then welded to prevent the two sections coming lose under load. The photo’s below shows the shafts after machining and when they have been welded back together. Once this was done the rack was reassembled and fitted back onto the car. At this point I was unable to proceed any further as the rod end bearings I had bought don’t have enough movement. This means I need to buy some high angle misalignment rod end bearings to complete the modification.

 

 

The first photo below shows my home made bump steer gauge. Why pay loads of money for something that can be made out of a few items I had laying around the garage. The only Item I had to buy to make it was the piano hinge. The only issue with it so far is that the piece of wood that is attached to the hub is not perfectly flat but this doesn’t cause much of an error when the bump steer is so bad on the Marcos car. I will probably replace the piece of wood with an aluminum or steel plate at some point in the future but this won’t be required unless you are trying to measure the bump steer on a car where it’s almost zero.
The other thing I’ve done is fit a set of tubular wishbones. The lower ones are none adjustable, however the top ones are adjustable. This means I should be able to set the camber and caster of the front suspension. The only modifications I plan to do in the future is to narrow the steering rack by about 50mm and then modify the track rod ends so the height of the mounting point can be adjusted. Once this modification is done I’ll spend some time trying to set the cars suspension geometry up and I will have hopefully solved the problem of bump steer.