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MG Midget and Sprite Technical - Kingpin lower fulcrum play?
I'm slowly getting my midget back together - hope to be able to re-start the engine this weekend = yay.
I've started to re-assemble the front suspension, worked around some issues with the cork sealing rings not fitting well, but now have a possible kingpin problem. The offside upright assembly went together fine, and moves freely, but the nearside kingpin was a tighter fit in the upright and is a little stiff in the steering axis (probably not stiff enough that you would notice it at the wheel). I've not filled them with grease yet, just a smear for assembly.
The main issue is that the kingpin is a slightly loose fit in the wishbone, so there is a little fore-aft movement in the kingpin on the lower fulcrum pin. How much, if any, play is allowed here? I can't see that any is a good idea, but not sure how best to resolve it?
Thanks in advance,
|no fore/aft freeplay should exist between the kingpin and the wishbone. Play there indicates wear that ought to be addressed (usually, by replacing the wishbone). Separating the wishbone from the kingpin is not always possible without cutting the lower pivot, but you might get lucky.|
You also indicated one kingpin is tight, which means that you want to adjust the shims (located at the top)
|We need to be precise here - you say the "king pin is a slightly loose fit in the wishbone" which technically doesn't make sense. Then you say there is a "little fore-aft movement in the kingpin on the lower fulcrum pin", which does make sense. The reply by NK doesn't help as hes also mixing his king pin, fulcrum and wish bone references.|
There should be no free play between the wishbone and the fulcrum pin, and no free play between the fulcrum pin and the king pin. I have achieved the former, but not the latter, despite careful selection of rebuilt units.
I gave up the quest for elimination of free play, being satisfied with suspension that feels taut, is clonk free and passes the MOT, but I know deep down there is still some movement - Grrr
|S G Macfarlane|
|Is your fore and aft movement between the fulcrum pin and the wishbone, or between the fulcrum pin and the kingpin?|
Also, is your kingpin tight in the stub-axle with the top trunnion fitted and the nut tightened? If so, does it get looser when slackening the nut?
|Dave O'Neill 2|
|Hmmm, I'll try to explain it better, if this doesn't work, I'll dig out some photos.|
The kingpin sits between the two threaded tubes/bosses that the fulcrum pin screws into.
On my offside, this fits nice and snug, but on the nearside it does not, so there is a little fore-aft play along the length of the fulcrum pin, once the fulcrum pin is screwed in.
The fulcrum pins on both sides appear to fit quite happily in the wishbones bosses.
The kingpin which is slightly tight on the stub axle / upright, needed a bit of encouragement to get it through the upper bearing. I have not tightened the top trunnion yet.
The kingpin should be firmly attached to the fulcrum pin - secured with the little cotter pin - so that they move together as one. You will then get a little forward and aft movement as you rotate the king pin in relation to the wishbone so that the fulcrum pin screws along its thread. Other than that, there should be none, or at most very little, for and aft slack between the fulcrum pin and the two bosses that it screws into.
As for the tightness on the stub axle it sounds like you have mis-matched parts perhaps? Or have you fitted new bushes that need a bit more reaming?
I should add that I have not yet whacked the cotter pins into position, but I wouldn't assume that this would make alot of difference, or take any load.
I'll see if I can get a feeler gauge in there or somehow measure how much play there is.
Interesting point you make about the mis-matched part - I don't think I have switched the sides around during the refurb process, though the thought had crossed my mind to try swapping the king pins and see.
It could be that it was like this before I dismantled it. Foolishly I didn't check them first, as I knew I needed to get them apart to clean and fit new seals etc.
|surely the mating surfaces of kingpin and fulcrum pin are parallel not tapered, so there will always be fore-and-aft movement possible - until you complete the assembly with the cotterpin.|
|David - your correct - I guess you'll never get zero slop between the fulcrum pin and king pin. I investigated this in a previous thread, at the time (and even now) it didn't seem right relying on the cotter to take up all the play - as my early contributions (above) - I gave up!|
Now i just replace the cotter regularly before the rest starts wearing as well.
|S G Macfarlane|
The cotter pin does indeed lock the whole kingpin/fulcrum pin joint solidly. The fore/aft thrust is taken by the threads on the fulcrum pin and wishbone. There is no fore/aft loading thrust between the kingpin and the wishbone, clearance here is irrelevant other than for keeping dirt out and grease in.
|Just to add Pauls contribution: I had a nasty cloinck sound from the suspension. It turned out to be a cotter pint that had worked itself loose. So cotterpins tiny as they are do a big job in locking and tightening up the lower suspension point. So whack the pin and screw the nut not to tight because it will break buit tight enough not to work itself loose.|
This thread was discussed between 27/04/2011 and 28/04/2011
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