100M Brain Teaser

While preparing my Auction Report on 100M values for the February issue of Healey Marque (shameless self promotion) this came to mind. One of the indicia of a factory M is the bent crossbrace that was put there by the line workers who installed the hi-lift camshaft while the engine was in situ. But 100M's came with high compression pistons and they must have been installed before the engine went in. So why didn't the hi-lift camshaft go in when they were installing the pistons since that motor would already be dedicated for an M? And wouldn't the bent crossbrace be more likely to show up in a LeMans conversion where the engine wasn't going to be coming out? Enquiring minds.

Rick--

You said: "But 100M's came with high compression pistons and they must have been installed before the engine went in."

Perhaps they were not and the entire conversion/upgrade, etc. was done after the standard engine was installed. I know it makes little sense but never forget what we are dealing with. Or maybe they installed both HP pistons and cams beforehand and simply bent the brace as a sign of differentiation.

Michael Oritt said:

Rick--

You said: "But 100M's came with high compression pistons and they must have been installed before the engine went in."

Perhaps they were not and the entire conversion/upgrade, etc. was done after the standard engine was installed. I know it makes little sense but never forget what we are dealing with. Or maybe they installed both HP pistons and cams beforehand and simply bent the brace as a sign of differentiation.

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Mike,

That's the only thing I can think of is they were installing the pistons on the line, too. What a PITA that must have been and wouldn't it just have been simpler to have a bunch of M engines built up and installed in the chassis in the first place? I'm assuming, but am not sure, the bodies with louvered hoods were shipped from Jensen to Longbridge where the motors were installed. So they would have known right from the start which car was going to be an M. Were they removing the standard shocks on the line, too, and replacing them with the heavy duty ones? Someone with way more 100M knowledge than me must have the answer.

I am thinking that the m modification was developed well after the procurement and assembly line was established. In that when they decided to make the M they just pulled cars from the assembly line. I have no immediate recollection of facts to support that though.

Editor_Reid said:

Cars destined to be made into 100M models were not pulled off the assembly line at random. Jensen sent the chassis/bodies to Longbridge with the bonnets already louvered, and these cars were specifically pre-designated to become 100Ms.

As I have always understood it, they were completely stock, standard cars when they arrived in Warwick, with the exception of the louvered bonnet. In other words, all changes to make them 100M models took place at the Donald Healey Motor Company (DHMC), with that sole exception of the bonnet being louvered by Jensens. Of course that included the internal engine changes. There was no such thing as ordering a "100M engine" to be delivered for installation in a car destined to become a 100M. The engines became 100M spec at the DHMC.

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So the cars with louvered hood went from Jensen to Longbridge where the engine was installed then to DHMC to make it into an M. But if the standard motor is in the car when shipped to DHMC, were they installing the high compression pistons there with the motor still in the car? That means removing the head, carbs, exhaust, oil pan, just to get to the pistons then remove the rods with the pistons and install the high compression ones. Sounds crazy.

Cars destined to be made into 100M models were not pulled off the assembly line at random. Jensen sent the chassis/bodies to Longbridge with the bonnets already louvered, and these cars were specifically pre-designated to become 100Ms.


They were completely stock, standard cars when they arrived in Warwick, with the exception of the louvered bonnet. In other words, all changes to make them 100M models took place at the Donald Healey Motor Company (DHMC), with that sole exception of the bonnet being louvered by Jensens. Of course that included the internal engine changes. There was no such thing as ordering a "100M engine" to be delivered for installation in a car destined to become a 100M. The engines became 100M spec at the DHMC.

Side note: I have heard, from reputable sources, that the engines were supposed to be removed to fit the cam--and, presumably, the pistons--and when DMH or Geoff were watching they were, but the mechanics took a short cut when they weren't and pulled the cam out from the front. So, some 100Ms may not have a bent crosspiece (mine does).

HealeyRick said:

So the cars with louvered hood went from Jensen to Longbridge where the engine was installed then to DHMC to make it into an M. But if the standard motor is in the car when shipped to DHMC, were they installing the high compression pistons there with the motor still in the car? That means removing the head, carbs, exhaust, oil pan, just to get to the pistons then remove the rods with the pistons and install the high compression ones. Sounds crazy.

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Just changing the cam requires draining cooling system and removing radiator, removing distributor(it needed to be changed), removing oil pan and oil pump, removing rocker cover and rockers, removing pushrods, removing intake(it needed to be changed to M-style) and exhaust manifolds to access lifter cover and lifters. Not that much more work(11 head nuts) to pull the head at that point. The head also need to have the valve springs changed. Also, the M had a different, slightly thinner head gasket. Stock was a copper/composition/copper unit. The M gasket was steel/composition/copper.

It seems it would have been easier to have converted engines ready for installation on the assembly line, but maybe their system just didn't allow for that.

I have read that the techs at DHMC were supposed to be pulling the engines out for the conversion work, but clearly, someone figured out it would be quicker if done in place. Word was that Donald did not approve of this.

And the myth goes on....

I just noticed that Bob beat me to some of the info. I guess I shouldn't have stopped for lunch before finishing my post.

Michael Oritt said:

And the myth goes on....

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And which myth would that be?

Craig--

No offense meant to anyone or anything. M's just seem to stimulate much attention, speculation, and of course misrepresentation".