These have an aluminium block that adapts the starter to the cylinder block. The starter is bolted to the adapter and the adapter to the block. The bolts that attach the adapter to the block are stout enough but the bolts that attach the starter to the adapter are skinny little things, looks like about 3/16. Why they don't shear off is beyond me. Yesterday mine came loose from the adapter. It just spun when I turned the key, sounding like one does when the ring gear is hooped. I managed to roll back out of a driveway and then down a hill and gear started it. When I got it home and jacked it up I found and rectified the problem. I used plenty of Loc-tite this time. The drive gear on these starters are not as heavy as the stock ones are, so I will have to replace mine as it was damaged trying to start the engine while hanging at an angle. Thought I'd pass the along, anyone in the process of installing one of these may want to ensure the starter-adapter bolts are firmly secured. Too bad they didn't have a method of locking such as lock wire or pin.
My take on aftermarket HI torque or aftermarket starters in general.
They are not for daily use. They are not for a daily driver. These starters do not have the build or "meat" if you will to last.
Even the OEM Delco starters have issues with heat soak in the solenoid..but overall..I have had OEM rebuilt starters in my daily driver Birds for 20 years without issue. I've also had reman starters with solenoid issues only. I have an aftermarket Powermaster in my 500 mile a year 520 hp 455 for the last 13 years with no issues. The issues I had was with my HI torque in my 67 daily driver that had the same issues you state. Honestly, I don't believe they are built with durability in mind.
You really need to disassemble and blueprint and add a heat blanket to these and do require removal and cleaning every few years.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
Banshee, My take on almost all aftermarket products is the same, not built as strong as OEM. and most of it doesn't fit or perform as advertised. Heat soak in the solenoid is only half the heat problems, the S wire from the starter switch gets hot and the resistance level goes way up, sometimes to the point there isn't enough juice to pull the solenoid closed. My GTO was bad that way, even with a brand new starter. I put a Ford style starter solenoid on with a buss bar from the battery cable terminal to the S terminal and my starting problems were solved. I put the mini starter on the Firebird for more header clearance.
Bigchief, Mine is an IMI Hi-Torque. Most of the Pontiac vendors sell them along with Powermaster, TCI, GPE. I think they are all the same starter motor, Denso Nippon, with different gear reduction and mounting units. IMI makes two attaching blocks one for the bellhousing mount on the 61-64 389-421s and the cylinder block mount, they also offer two starter motor power ratings Mine is 1.88HP, draws 175 amps at full draw and has a 4.1:1 gear reduction. The 16 position adapter block is handy for tilting the starter as far away from the header as possible. The starter motor has only been mounted for a few years, I was surprised it came loose. But perhaps I did not tighten it enough when I first installed it. May be the aluminium adapter between the cast iron block and the steel starter. Three different coefficient of thermal expansions.