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Identifying Wear in Throttle Linkages

Our PI cars of the 60s and 70s were built to a budget and probably had a design life of around 100,000 miles if the tin worm could be kept at bay! As such, there is not a single ball bearing or bronze bush in the throttle bodies, countershaft  or linkage rods. The nearest we get on early CP cars is the plasticised bushes in the countershaft, which were presumably used as they were less prone to binding than bronze bushes if the alignment wasn't quite right during assembly. On later CR cars, the 2 levers in the throttle mechanism get bronze bushes. Everything else runs metal to metal and wear occurs everywhere, including in the bushes previously referred to.

Butterfly Spindles

 

The spindles are brass with mild steel levers that are secured with a nut on early cars, and solder on later cars. The brass butterfly spindles run directly in the aluminium castings.

 

There is no facility to lubricate the spindles. The soft brass spindles wear significantly more than the aluminium casting. The wear on the spindle occurs on the opposite side of the spindle to where the force is applied.

CP throttle spindle identifying wear

On CP spindles it occurs at the lever end at the 10 o'clock position (if you were looking at the rod end on with the spindle in the throttle body). With the butterflies slightly open, so they are not holding the spindles in position, try moving the lever in the 10 o'clock to 4 o'clock plane. Any movement is due to wear in the spindle. The CP countershaft has separate linkage rods which enable wear in the linkages and spindles to be adjusted out. Synchronisation and a good tickover can be maintained with worn spindles until the wear is so bad that enough air is sucked in along the spindle bores to produce a high tickover speed, even with the idle air valve fully closed.

On CR cars there is a sequential operation of the butterflies as the spindles are connected and operated by a single linkage rod. When there is no wear, this system is superior to the earlier CP linkages as it can be quickly and easily adjusted using a screwdriver without even having to remove the plenum. However, wear on the spindles cannot be adjusted out. Any play on a spindle is taken up before the rotational force is transferred to the next throttle body. With worn spindles on the CR setup, it is possible to rev the engine by operating the throttle mechanism a small amount, which will open the butterflies in the front throttle body before those in the second and third throttle body open. If you adjust the play out, the butterflies in the middle and the front throttle bodies will be open to varying degrees at idle, so you will have an unacceptably high tickover.

Butterfly spindle wear in CP and CR cars can be completely eliminated by line-boring the throttle bodies and fitting sealed ball bearings.

Butterfly Spindle Levers and Top Swivel Posts

 

Both are originally made from mild steel and should wear equally. Avoid linkage rods with stainless steel swivel posts as stainless is harder than mild steel and the holes in the mild steel butterfly spindle levers will wear more quickly. This will necessitate replacement of the butterfly spindles on later cars that have levers soldered onto the brass spindles.

 

As can be seen in the photos, wear can be significant elongating the hole in the lever and cutting through the journal of the swivel post. Wear can be reduced by regular lubrication.

 

If you have butterfly spindle bearings fitted in your throttle bodies, the spindles will never wear but the holes in the levers will. As such, it makes sense to have the early type spindles fitted with removable and replaceable levers. There really is no point having bearings fitted if the later type butterfly spindles with soldered on levers are fitted, as the unworn spindles will need to be replaced when the holes in the levers wear.

Worn butterfly lever arm joint
Lucas PI Throttle Linkage Wear

We remake original specification linkage rods and swivel posts in mild steel for all PI models. We also remake butterfly spindles with replaceable levers for all CP and CR cars.

Linkage Rods

On later rods, the top swivel post rotates freely on the rod and is secured using a locking washer. The rod and the drilling in the swivel post wear, resulting in unwanted play. The screw slots in the top of the rods get broken off.

We remake original specification linkage rods and swivel posts in plated mild steel for all PI models.

CP Countershafts and Bottom Swivel Posts

On CP TRs and early 2.5PIs with the short countershaft levers and linkage rods, the bottom swivel posts wear, but the corresponding drillings in the countershaft do not wear.

On later CP 2.5PIs with the longer countershaft levers and linkage rods, the bottom swivel posts also wear, and so do the corresponding drillings in the countershaft.

On both countershafts, the plasticised bushes go hard and wear. We have seen numerous home-made quick fixes including the use of electrical junction box rubber grommets.

We remake original specification linkage rods and swivel posts in plated mild steel. We remake original spec CP countershafts for all PI cars and recondition original countershafts.

 

We have a range of countershaft bush upgrades which include SuperPro polyurethane bushes, bronze Oilite bushes (not to be confused with inferior brass) and self-aligning sealed ball bearings.

CR throttle mechanisms identifying wear

CR Throttle Mechanism

 

The CR throttle linkage mechanisms have quite a hard life, as a single rod and lever mechanism carries all of the load to open the butterflies in all 3 throttle bodies.

The usual quick fix for worn butterfly spindles and high tickover is to add additional or stronger return springs, which adds load to the mechanism and accelerates the wear.

The single throttle linkage rod is a longer version of the 3 used on the CP setup. Despite having to take 3 times the load, it is not beefed up in any way, so it wears in the same way as the CP rod described above, but at a faster rate.

The bottom swivel post attaches to the lower lever in the throttle mechanism. Again the drilling in the lever is the same diameter as those on the CP units despite it doing 3 times the work, so again this wears at an increased rate.

In the throttle mechanism, one lever acts on another to enable more precise throttle control in the first stage of opening. A nylon roller on the first lever operates the second lever. This roller often becomes seized and ends up with a slot worn in it.

We remake new and reconditioned original throttle and choke mechanisms, for early and late CR cars.

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