Motorsport Mickey

As JohnC says above, and as I said in my prose, if the hole is stripped it’s o/d is the correct tapping size for 3/8” UNC to take the 3/8” UNC studs without drilling further. For any threaded holes remaining, they thread form for the 5/16” UNF studs are very shallow, and being formed in alloy very much wants to drag your 5/16” dia drill into it. However I should caution against NOT using a jig to drill out the piddling remaining alloy threads. You do have to hold the drill at 90 degrees in 2 planes as you drill, and risk having studs leaning at angles if the drill is not controlled closely. Mick Richards

Andy, Sorry to depress you, but these trailing arms and helicoils mislead owners into the wrong choice. We’ve discussed before that these arms had the small blocks on the casting of inner diameter of the hub retaining aperture, placed there by an apprentice of about 3 months training. Unfortunately he was a dipso even at that young age, and his placements of the blocks left a lot to be desired. The standard 5/16 th UNF studs will often only ( just) be retained within the placed block, threatening to break through the side wall, any increase in the hole dia by fitment of the 5/16” UNF Helicoil, requires the hole tapping diameter to be drilled out to .328 thou. The original 5/16” UNF tapped thread to take the 5/16” UNF studs often degenerate into a grey collection of granuals which spill from the hole when you undo the 5/16” UNF studs leaving you with a neat 5/16” hole in the trailing arm hub surround, totally unencumbered by ANY remaining thread form…whatsoever. The fitment of the aforesaid 5/16” UNF Helicoil requires this 5/16” sized hole of .312 to be opened up to the tapping size of .328 thou removing a further 16 thou from the wall of the trailing arm. The Helicoil is a thread of 5/16” UNF sat within a larger thread which is tapped into the larger .328 thou hole in the trailing arm, this often breaks through the material in the blocks of the interior hub aperture in the trailing arm. WHEREAS… the 5/16” stripped hole left by the corroded alloy as it drops from the trailing arm…has an overall dia of .312 thou at it’s stripped dia, which co incidentally is the tapping size for…3/8” UNC thread form. You don’t even have to drill out the holes of 5/16” dia that originally were tapped 5/16” UNF to take a 3/8” UNC tap ! just bang the 3/8” UNC tap straight in there. This means… The hole has 16 thou more material left in it than a helicoiled hole, giving more material ( not much) retaining the hub. The hole ( if you so wish) can be deepened by drilling a 5/16” dia hole another 3 mm into virgin trailing arm material at the bottom of the hole, increasing the thread depth and increasing the stud retention capability against stripping. The original trailing arm holes can be used WITHOUT drilling, their stripped dia is the correct tapping size to take the 3/8” UNC tap, this means a jig is not required to accurate drill the holes to take the studs. The 3/8” thread form has more material across the throat of the thread ( it’s a bigger thread) resisting stripping better. As detailed in technical journals In an alloy, a UNC (Unified Coarse) thread form is generally stronger than a UNF (Unified Fine) thread form of the same size, particularly in the context of the female thread (the tapped hole in the alloy material). Detailed Breakdown Shear Strength: UNC threads have a deeper thread profile and more material in the cross-section of each thread, which provides better shear strength in softer materials like aluminum or other alloys, making it more resistant to stripping. Tensile Strength (Bolt): For the male fastener (the bolt itself), a UNF thread typically has a slightly larger minor diameter, resulting in a greater tensile stress area at its core, which makes the bolt itself marginally stronger in tension. Engagement: The overall strength of the joint, however, often depends on the engagement in the female (alloy) material. UNC's coarser pitch is less likely to strip the threads in the alloy, providing a more robust connection in this specific material. Vibration Resistance: UNF threads offer better resistance to vibration loosening due to their smaller helix angle and more threads per inch, creating better self-locking characteristics and a tighter fit. Application: UNC is typically used for general-purpose applications in softer materials where quick assembly is needed and thread damage or corrosion is possible. UNF is preferred in hard materials and for precision assemblies, such as in aerospace or automotive engines, where high clamping force and vibration resistance are critical. Therefore, when working specifically in an alloy material, the UNC thread provides a more reliable and stronger connection in terms of preventing the threads from stripping out of the alloy itself. Also in this application… The holes on this 6 stud configuration in the hub wall on the trailing arm require their centres to be drilled within fine limits, hence the application of a “jig” to drill through, to ensure the drill bit is square in two planes, avoiding the drill bit leaning over and moving the stud centre away from it’s intended position. This movement of stud centre will prevent the hub sliding over the studs, and require hole diameters to be increased in the hub to allow it to slide over the studs. And lastly, as a bonus you can in place of the studs use 3/8” UNC cap head set bolts to retain the hubs. This means the hub can be leaned over enabling any slight misalignment to be “ juggled” into place as you wind the bolts through the hub retaining holes. If you need any recommendation for this, it’s what many of the racers with IRS suspension cars use to keep their rear trailing arms on. Mick Richards

Err… holding the sump up I normally lift either a bottle jack or trolley jack underneath and balance on a pile of boxes or timber to get it within the jacking range. Then holding the sump in position, pump up the jack, when you get the sump within an inch or so of the bottom of the block, you can let it go. If it overbalances the outer edge of the sump contacts the block bottom and is prevented from falling off the jack. Then using 3 or4 inch set bolts I screw 2 into place, one either side down the block length. You can then remove the under sump jack and packing to floor level, and complete fitting the sump, lifting up the sump by hand so it slides up the longer bolts and screwing the sump bolts into position with the other hand. You can do this with the sump gasket and goo in position, it doesn’t touch the surface. Works for me. Mick Richards

It’s amazing what the non intentional “ chemical milling” ( as they call the reduction of panel thicknesses by chemical means) can remove from a car. Back in the 1970s intentional chemical milling could be undertaken by a convenient parking space on a beach in salt water, which would encourage more or less equitable panel thinning for weight reduction on monocoque body shells for competition use. (Wash thoroughly afterwards followed by rust removal and thin coat of stabilising paint). It sounds like the UK climate and deluges of winter salt had done the same to your shell Ian, you were carrying out your “overdrive top at 800 revs” pick ups with a drastically weight reduced TR2 ( always a “Skinny” car anyway) probably down to 600-700 kg weight, and therefore having “torque in hand” to overcome the imposed inertia ! lol. Mick Richards.

I’m told some are, but don’t tell anyone . Some get away with it. Mick Richards

Back in the day using 87 mm pistons I used to take .130 thou off and run at 11.3 :1 comp ratio. Basic problem with TR heads in those days ( and even worse these days) was not what you were taking off the deck surface, but what age and rust had eroded from inside the water jacket the other side of the squish area. The ages old “ stake support system” was employed then, and will still work to preserve the Squish areas. Mick Richards

But I presume the alloy is a thicker material ? Mick Richards

Mike, That’s a nice fitment of a rear firewall bulkhead. You’ll find it will help stiffen the shell of the car, but until you finish it with the small tabs fixed and sealed into place across the tops of the wheelarches, it’s only 50% done. The completed sealed firewall helps with keeping fumes away from the cockpit and driving compartment. BUT more importantly one fine day when you are out for a drive accompanied by a friend or partner you may have the misfortune to swerve to miss a dog, and the sliding car ever so slowly as the wheels hit the kerb, topple over onto it’s side and then onto it’s roof. If the windscreen surround doesn’t get flattened and the roof whether a soft top or even a rear backlight of a Surrey will likely collapse, you’ll be sat there in your seatbelts thinking…”that was lucky.” When the split rear fuel tank allows 10 gallons of petrol to flood into the boot and an electrical short or sparks from the slide along the tarmac ignites it…”whoompf”. That’s when you think, “ I’m glad I completed the job”. This description isn’t as fanciful as you may think sat drinking a cup of coffee, we have lost more than 1 member of the TR owning community to car inversion ( I’ve seen 3 happen, and all at speeds under 30 mph). Do finish the sealing off of the firewall, Triumph thought that a 3mm hardboard panel with half a dozen screws was acceptable, experience shows that it isn’t.

Hi Roger, A nice fitment, I can see you’ve drilled or punched 2 holes ( these are for plug welding I assume ?) where the reinforcement attached to the bonnet seam, and spot welded along the bonnet side edge. Have you welded along the diagonal edge where the support plate touches the bonnet skin ? Or left that area because of “ dimpling” on the top showing bonnet surface ? Regards Mick Richards

Hi Fernando, You say “ the oil pump axle” which I think you mean the oil pump rotor shaft. The shaft and the “ rotor”…the star shaped pumping shape at the end need to be securely fixed together so when they rotate the oil pump housing creates a squeezing and pumping motion to pass the oil out and around the engine. The original pumps were “ staked” ( a press squeezed the outer rotor onto the shaft securely), preventing the shaft from becoming loose and stopping the oil from being pressured around the engine. There were a bad “ batch” a collection, of pumps made sometime in the past…maybe 30 years, which didn’t have a secure “ staking “ of the shaft and the star shaped pumping piece together. Then sometimes in use ( even maybe after being used ok for years) the two parts became loose and the pumping action for the oil stopped, which can give big problems with possible engine damage. I would take the engine out, and strip the moving parts, big end, main bearing caps, camshaft and followers etc to see if any damage or excess wear has happened. If so parts will need replacing, hopefully just bearing shells and not major components. When you replace the oil pump, carefully check the fitting of the oil pump star drive onto the shaft, trying to spin the shaft within the drive part. For peace of mind I would drill a 3 mm hole through the drive and into the shaft and then drive a 3 mm dowel through the drive and into the shaft ( making sure there are no protrusions and that the pump will work as intended) to prevent any possible movement in future. I hope your damage is not too bad, unless your mechanic was aware of the parts failings in use it’s likely he expected the part to perform as it should. best regards Mick Richards.

And they almost certainly a better welder than I with their eyes closed ! Makes me sick lol. Mick Richards

I think you have to consider, when Porsche decide that fitting Pirelli CN36 to their cars as standard equipment from the factory as a benefit, to allow Porsche owners to prevent their cars “swapping” ends when grip becomes scarce they may have tested and considered ALL other tyre options. ..I did. My purchase of CN 36 for competition especially, was a good decision that paid off in competition against other tyre shod cars, their performance in the wet especially gave an edge over lesser tired cars, and proved to me that fitting them for road use is a sound decision. Exactly as the Longstone Tyres published tests above prove. Admittedly they cost more, but balance that against enhanced safety and lesser likelyhood of a total rebuild after stuffing the TR under an Artic ? That is a strong selling point. Mick Richards.

Just to clarify, it’s the English team which has won. Obviously a part of the islands of Great Britain, but because everybody whose in the team is English ( apart maybe from Meg Jones, who is Welsh, born in Cardiff with a a Welsh mother and English father, but we’ll draw a veil over that). Mick Richards

Yep. I think buying a 5 is fraught with danger. I don’t know enough “ tells” to define which is a TR 5 and which were TR4a with added 6 cylinder engines and “ dressing.” Or an imported TR 250 often described as “an American TR5”, which has then been Anglicised with more dressing, to help convince unwary buyers into parting with £40-50k for a bitsa described as a TR5, as against the TR 250 purchasing range of £30k ish for an excellent car. I fear there may be disappointed current owners as the truth outs, or disappointed future owners as the “ mistake” is carried over to new owners Mick Richards

Every year numbers our original design TR4a/5/6 hubs and stub axles are harvested by old age, driving damage, and renovation damage, and the owners are the test pilots who drive them…to destruction. https://www.trforums.com/uploads/monthly_2025_01/image.png.3eb5d0ea099039768e66756b8e17b804.png Keep an eye and an “ear” open for clicks, squeaks or other unusual noises, it is as well to have them checked by a TR specialist if you are unable to satisfy yourself as to what they are. Mick Richards