Marlin Roadster (Re)Build

[peterux]

Nice work, Robin.
Was there a reason for the bottom trunion being threaded? It seems an odd thing to do?
How do you keep the new thread lubricated, maybe some waterproof marine grease?

[MartinClan]

Originally Posted by peterux

Nice work, Robin.
Was there a reason for the bottom trunion being threaded? It seems an odd thing to do?
How do you keep the new thread lubricated, maybe some waterproof marine grease?

The upright rotates in the trunion using the thread. It effectively un-screws and screws-up a little every time you turn the steering wheel. It's ancient technology inherited from the Morris Minor. Quite why they didn't fit a balljoint instead I will never know. There is a massive balljoint at the top of the upright where it joins to the top arm. They could have put similar at the bottom.
The thread is lubricated using one of the 2 grease nipples on the trunion. The original design only had a single grease nipple which is why not much grease ever reached the thread. And made worse by lack of regular maintenance.
My guess is that the majority of Marinas still out there have worn threads on the upright. I think as long as you fill them full of grease before the MOT the tester doesn't notice.

Cheers, Robin

[peterux]

Thanks for the explanation, Robin.
I guess it was probably a cost thing?
I had an Austin Healey Sprite (aka Midget) that had threaded fulcrum pins that wore out the lower wishbones in the same way. We lived in a terraced house then and I can remember changing the wishbones in the gutter outside the house.

[Mick O'Malley]

My ex-REME tester threw up his arms in horror when he discovered I'd greased my trunnions. He insisted that Hypoy should be used, so I mended my ways, bowing to his superior knowledge.

Regards, Mick

[AlanHogg]

Morris Minor /Marina trunnions should be greased. Certain Triumphs eg TR6 and Reliant Scimitar which use TR trunnions should be gear oil. that said its always been a bone of contention within the Triumph group.

[MartinClan]

Doing a bit more on preparation.

First the front hubs. The good news was they still had the original Timken bearings - or so I thought.... However when I looked at one of them it was totaly trashed inside. It looks like a bearing had broken up at some time judging by the damage. Even the step which locates the bearing outer race was destroyed. Someone had done a quick fix and popped in a new bearing but that's not really an acceptable solution so I am looking for a replacement.
damaged hub by Robin Martin, on Flickr

And the brake calipers. They are almost the same as those used on the Triumph Spitfire (Girling type 14) so there are plenty of replacements available. But, after experience with buying bits for the engine I am a bit suspicious of some of the stuff that is available. So I thought I would have a go at stripping them - keeping in mind they are at least 50 years old and haven't seen any use for at least the last 30!
Following a good tip I cut the end off an old flexi brake pipe, screwed the uncut end into the caliper and used my compressor to blow down the other. This allowed me to have the caliper safely in a bucket at arms length just in case any of the pistons came flying out!
Three of the four came out "easily" but the last one wouldn't budge.
Now I followed another good tip! I put back the piston in the caliper with the stuck one but in an almost out position. I then filled the caliper with water (yes really) with the bleed nipple screwed up and then a spare bleed nipple where the brake line should go. I used a couple of clamps to push back the "good" piston and Hey Presto the water pressure was sufficient to get the stuck piston moving! Amazing!
Finally I split the calipers. You are not supposed to do this but I couldn't see any other way of properly inspecting and cleaning the bores. There is only a single O ring to worry about and this comes with the refurb kit you can get from Bigg Red. And, suprise suprise, everything looks good even though there was rusty crud in most of them!

stripped calipers by Robin Martin, on Flickr

[MartinClan]

I have made some new adjustable tie bars following what has been done in the past by other Marlin owners. They comprise the front part of the old tie bar, a turnbuckle and some rose joints. The idea is not so much to make the suspension adjustable but to be able to dial out any inaccuracies in the chassis geometry. From what I have read this is not uncommon. I am going to remake the U shaped chassis brackets as I don't think my first attempt looks substantial enough.

tie_bar1 by Robin Martin, on Flickr
tie_bar2 by Robin Martin, on Flickr

Cutting the 1/2" UNF thread on the tie bar proved tricky. Ideally a lathe should be used for larger external threads but I don't have one. I do however have a decent pillar drill - so I used this to drill a perpendicular 1/2" hole through some substantial box section. I then attached this to the die holder positioning it with a 1/2" UNF bolt. The hole through the box section acts as a guide resulting in a perfect thread on the item to be threaded.

modified_die_holder by Robin Martin, on Flickr
die_holder_use by Robin Martin, on Flickr

I should say the guide wasn't my idea. I found the basics on t'internet after a failed attempt at cutting a thread.

[Dpaz]

What a brilliant hack and so simple. Thank you! But did you forget to mention the cap screws, or did I not read it right?

[MartinClan]

Originally Posted by Dpaz

What a brilliant hack and so simple. Thank you! But did you forget to mention the cap screws, or did I not read it right?

Yes - over simplified description! Once positioned using the bolt, you attach the box section guide to the die holder using whatever mechanism suits. I just drilled through the die holder and box section and use a couple of M4 screws.

Cheers, Robin

[MartinClan]

Front suspension rebuild has moved on to fitting the hubs. At this stage I was feeling fairly smug with the bargain triumph wire wheel adapters I had bought from Ebay as a trial fit seemed to be good.
However when I came to fit them properly I found they didn't (fit). The hub casting, where the grease cap fitted, fouled the inside of the adapter. "Easily" fixed by some heavy duty filing. I then found that the wheel studs have a large shoulder on them, great for centering the wire wheel adapter, but unfortunately preventing the nuts securing the adapter to be screwed fully home. Hmmm. after some head scratching I made a thin, 1mm, spacer which did the trick. now everthing fits OK :-).
So the front suspension is pretty much complete and I would have a rolling chassis - if my wheels had any tyres on them,
Some pictures....
hub_before by Robin Martin, on Flickr

hub_and_spacer by Robin Martin, on Flickr

front_suspension1 by Robin Martin, on Flickr

[Patrick]

Looking good