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MG MGA - Swivel Pin

Have finally tracked down a front end clunk - which has turned out to be loose swivel link. The vehicle had a new swivel pin fitted by the previous owner and the vehicle has since sompleted about 35,000 miles - lubricated per manual.

My question is about the diameter of the swivel pin - although it's is newish, I question the quality of the part and wonder if the pin is also worn / slightly undersize. The diameter is 0.773. Does anyone have an original pin that can be measured for comparison. Any help would be appreciated.

Russell
Russell

Russell,
The swivel link itself, part no. 3 in the manual, should be a good fit on the king pin. It should turn easily on the king pin (acme thread) but have not slop. The distance tube, part no 46 in the manual, should be about .748" diameter and 2.337" long. It should also have no slop in the swivel link bushing. When you install new bushings in the swivel link you should ream the bushing them with a .750" reamer. I am rebuilding a Coupe front end and we found the swivel links had much side to side slop on the king pin, acme threads worn out, so we had to replace them along with new bushings and distance tubes. You do not want any slop in your front end fits. Have a good day!

John
John Progess

Hi Russsel. In regard to the threaded ends of the swivel pin, and the "acceptable" amont of wear, my 1500 factory manual states "When new, these are a free turning fit, without slack. AN appreciable amount of slack is permissible in these threaded bearings, and they do not require renewal unless very slack." While it is alway preferable to aim for minimal clearances in the swivel pins, it is clear from the manual that a fair bit of slop was deemed by the factory to be perfectly acceptable. Personally, I ran my MGA for about 5 years with one kingpin that had considerable slop in the top swivel pin thread. Even with the noted slop, front end alignment was acceptable, and tire wear on that side was extremely negligible! When I finally did replace the worn swivel pin, the upper thread was quite noticeably worn, and there was what I felt to finally be excessive slop. The front end on the bad side had started to make just noticeable clunking sounds when going over bumps, and this prompted me to finally replace the known to be sloppy swivel pin. I have read that the threaded swivel pin system is excellent, and apparently has considerable bearing area on the threaded portions of the swivel pin. Presumably this design feature allows extended use even when there is more than desirable slop in the threads. With safety in mind, the question becomes when does the amount of acceptable slop reach the limit, and replacement of the swivel pin become essential? For me, a twice yearly inspection of the swivel pin, and amount of slop became a ritual. When the amount of slop was personally considered excessive, and front end clunks became noticeable, I replaced the swivel pin immediately. Ideally, swivel pins should perhaps be replaced before a front end clunk is noticed, if there is considerable slop in the threads. Of course, this is my personal observation and experience, and perhaps other readers will disagree. Hope this helps, Glenn
Glenn

Thank you John & Glen I believe the swivel pins are long wearing, so having travelled a distance of only 35,000 miles and with proper lubrication the part should be like new.

Interestingly, I have the history of the car back to 1975, at this time the engine was replaced - it is a 1960 1600 built in the latter part of that year. The only reference to repair / replacement of either the swivel link or swivel pin is in the late 90's when the previous owner decided to complete a body off restoration. It was during this restoration that the right swivel pin was replaced. The car went back on the road in 2002 after my purchase and has been lubricated per the workshop manual eversince.

My concern is the swivel pin being a re-production part may be inferior, either in the hardness quality and has subsequently worn or the part may have been undersize. So I am wondering if anyone has an original (not repo) part that could be measured giving the outside diameter across the threads. If original parts are close to 0.773, then at least I will know this part is ok. I am reluctant to purchase another swivel link, if the pin is a major cause of the free movement.

The left side parts which as far as I can determine are original and have no noticable movement.

Hope someone can help.

best wishes

Russell
Russell

Hi Russel. Playing devil's advocate, perhaps the swivel pin is not the problem. Perhaps the thread on the trunnions are worn?
Again this is just a thought about another possible explanation for the slop you have noted. Cheers, Glenn
Glenn

Glen yes, the swivel link is very worn, both in the bush and thread. My suspusions were raised with the swivel pin when I checkd some receipts from the previous owner and found that a new swivel pin had been installed.

Today I was able to measure four (2 each of left and right) different original pins. One was bent and had been taken out of a car a number of years ago, and other than the bend appeared in good condition. It measures 0.784 both top and bottom. Another was visably worn and measured 0.784 & the worn end at 0.755. The third measured 0.784 & 0.7825. The fourth measured 0.784 & 07835.

Each of these was original swivel pins - so my guess is the original diameter was 0.784. The replacement pin which has 35,000 miles of use measures 0.773 at the top, and I now suspect it was manufactured undersize.

Russell
Russell


I have recently had a lower trunion fail and upon investigation found it to be made of brass, I think that it belongs on a TF or some other antiquated chariot. A quick check with a magnet confirmed our other A to be made of something ferrous.
jim mckenzie

I'll bet that got your attention. My '59 has oversize studs holding one of the front shock absorbers to the frame. Dad said when the originals pulled out, it was kind of exciting.
Del Rawlins

Early (and many repro) trunnions are made of Brass. The early A trunnions were the same as TF ones.

I have a used set of steel ones if needed, and a complete set of 1600 front axle stubs, swivel pins and trunnions as well.

I have brass trunnions on my car at the moment.
dominic clancy

The trunnions and swivel pin set I got for mine were bronze and reamed ready to fit and were perfect. The pins and trunnions should both be replaced as each wears to an oval shape. Remember to check the end clearances and the correct hardened shims are fitted. Mine had plain steel 1/2" washers!

You speak of such slop at a low mileage. I have heard of a local garage (now disappeared thank goodness) who had replaced the swivel pins on an MGB, which was for sale, to get it through our MOT at a testing station. Prior to its sale all the original components were refitted!!! Could something similar have happened to your motor?

So anything's possible out there. Doing it yourself Russell, you know it's right.

Pete
Pete Tipping

Russel, I just removed one of mine on my 60 A Coupe to check them out. I concur that the swivel pin measurement on mine is 0.784 both top and bottom. I have a little wear in some areas down to 0.782. the inside dimension of the top and bottom tunnions is 0.724 to 0.725, slightly ovalled. The top swivel pin and upper trunnion is more worn, maybe had less grease getting to the top of the swivel pin.

The lower brash bushing measured 0.748 and the outside diameter of the lower steel sleve was 0.747.

It doesn't seem that there is much wear on mine and I can't feel any slop.

Andy
Andy Preston

Jim, would have been an exciting ride! I understand early MGA's also has brass swivel links.

Dominic, thanks however, managed to find some used parts. It looks as though the replacement swivel pin was not only slightly undersize but appears to be a UNC thread rather than ACME type as per original.

Pete, from what I can work out the replacement swivel pin was fitted just prior to my purchase - the bottom swivel link is brass and a perfect fit, however the repair stopped there. An (the?)original steel upper swivel link was screwed on to the assembley (maybe it was changed after the roadworthy). The problem is the replacement swivel pin does not have an ACME thread - and with some wear in the top swivel link the result a lot of movement.

Andy, thank you for the measurements - the used swivel pin I have managed to find is 0.784. Yesterday I was able to measure a NOS part still wrapped in gease paper, packed in a cardboard tube marked BMC. It measured 0.7835 - so that confirms the 0784 measurement we have both discovered. I have not compared the ID of the swivel link(s), however with your measurements now I can also check these parts.

Thanks very much for your help all.

best wishes

Russell
Russell

This thread was discussed between 05/01/2007 and 11/01/2007

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