[Healeys] 100 engine rebuild

Bob Spidell bspidell at comcast.net
Tue Nov 7 09:16:30 MST 2017

100 crankshafts are known to break if driven much over 4K RPM (and 
possibly at lesser speeds).  If I was going to mod a 100 engine--and was 
filthy rich--I'd look into a billet crank or whatever treatment could 
improve the strength of these.  Some definitive info here:



On 11/6/2017 1:22 PM, WILLIAM B LAWRENCE wrote:
> Gary,
> I just started my engine after about 2 years of rebuilding. Sounds great.
> I installed 88.5mm pistons from Denis Welch. They are sized precisely 
> enough that the machinist just has to bore to the nominal size and 
> they fit. They incorporate new tech metric piston rings to minimize 
> blowby. So far they are performing as advertised. They also sell these 
> pistons in 88mm and 89 mm. I think there is a lot of meat in the block 
> and I've heard of people overboring them to 0.100"
> I also installed their performance head gasket which is a MLS 
> (multiple layer steel) design. This is supposed to eliminate the 
> typical leak at the number plate.
> I'm running an iron head which had never been cut and tested with no 
> cracks. How many of those have you seen recently? I'm running an 8.5:1 
> compression ratio.
> I'm using a set of H6s that I built up from spare parts on a set of 
> Denis Welch manifolds with their heat shield. For jetting I just went 
> with the 100M spec OA6s. I plan to run it on a chassis dyno to check 
> the mixture and adjust the tuning (Burned a couple pistons a while 
> back so I'm very leery of pinging.) I've added a set of 2-3/4" 
> velocity stacks and a  Pipercross double air filter. This 
> will just fit under the shroud but I've got to have a hatch fabbed 
> into the shroud to allow for servicing. Fortunately I've found a good 
> sheetmetal guy who is refurbishing the shroud as we speak.
> The camshaft has been ground by Iskendarian to their Z-99-E4 
> specification (I have been running this specification for over 10 
> years). It has durations of 260 degrees and a valve lift of .425". 
> These numbers are a little more radical than the 100M/S grind, but it 
> runs smoothly without a noticeable lope. I sent them a used camshaft 
> and they ground it and heat treated it for $135 plus shipping. I 
> bought Denis Welch's vernier cam sprocket and I've set the cam timing 
> ahead 4 degrees to optimize low end torque. I am building the car for 
> long distance touring and with 3.54:1 final drive gears I doubt if 
> it will spend much time over 4,000 RPMs.
> Good luck with your project.
> Bill Lawrence
> BN1 #554
> ------------------------------------------------------------------------
> *From:* Healeys <healeys-bounces at autox.team.net> on behalf of 
> warthodson at aol.com <warthodson at aol.com>
> *Sent:* Sunday, November 5, 2017 7:32:16 PM
> *To:* healeys at autox.team.net
> *Subject:* [Healeys] 100 engine rebuild
> I am beginning a complete 100 engine rebuild & am looking for advise.
> - I would like to build an engine that will produce as much power as 
> is possible consistent with the following specifications:
> Fast road driving, not road racing. Premium fuel, not racing fuel. In 
> the USA Approx. 91-92 octane rating. I think that results in about 
> 9.5:compression. What compression ratio would you recommend?
> The engine will include:
> -an aluminum head
> -Carbs: twin H6's
> I also need a new cam recommendation & am considering either Denis 
> Welch "#DW1 or #DW4 cam? Suggestions, please.
> Also, I would like to over bore the engine. Is there any reason to not 
> bore it out to 89mm, other than that might not allow for any future 
> over bore?
> What piston sources  would you suggest for this application?
> Any related suggestions, recommendations or questions would be 
> appreciated!
> Gary Hodson

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