[Healeys] 100 engine rebuild

Tue Apr 15 13:39:29 MDT 2025

 Gary, it sounds to me as if you're doing all the right things based on my Healey 100 rebuild several years ago. Yes, I had the block boiled as part of the machine-shop work. As for the parts, I also used a billet crank, 100M cam, alloy head, and all other parts from Denis Welch--the crank being the part that broke. These were rather spindly to begin with, and with that long, long stroke and but three main bearings, replacing it with a better and stronger crank is the only way to go. Same with the alloy head, as most original heads are warped, cracked, or both after 70 years-plus. You also want the best cam and especially rod and crank bearings you can buy—as in tri-metal, not just white metal, as original.
Three other suggestions: 1) Put in a rear lip seal while the engine and crank are out of the car. You can add on the seal to the later sixes with the engine and crank in place--but NOT on the fours. 2) Add a harmonic balancer to the front to help lessen the crankshaft-killing torsional vibration with that long stroke. 3) Again, to help lessen vibration, install a lighter flywheel. You don't have to go crazy light; 20-25 pounds should be just right, using, say a late BJ8 3000 flywheel. And be damned sure you use ARP bolts, not Moss cheapies, to install it, again available from Welch or AH Spares, paying careful attention to the torque settings; mine came loose (thankfully without killing me). I really liked Welch because of their technical assistance on not only getting the RIGHT parts but ALL the parts  needed. 
Some may see this as overkill for a car that isn't being raced. Don't listen to them; Healey engine rebuilds are EXPENSIVE and the idea is to do it just once! Best of luck ...
    On Tuesday, April 15, 2025, 01:13:16 PM EDT, Steven Kingsbury via Healeys <healeys at autox.team.net> wrote:   

 I rebuilt my engine a few of years ago in my BN1. I had never built an engine but figured at 72 years old, maybe I should learn by doing. Since you're having the engine bored, I had to have mine sleeved then bored, by all means get it "boiled" out at the same time. I did mine. Now mine was missing the engine plate already, so I didn't worry about that, but I had heard about engine number plates dissolving away during that process, so check with your machine shop. I also have a fast road cam, came with the engine, but I did get new bearings from MOSS and had my machine shop install them. I got my 100M spec pistons from AH Spares, 60 over. Long story on why those, but I made sure to take the piston to the machine shop so they could be the bore perfect.
So yes on all new bearings, get everything checked by your machine shop as far as all clearances, cam, crank, etc. Check all surfaces as far as mating, assume nothing and finally, I went with a new copper head gasket and blew that out in about 1200 miles! Had to redo the head, another long story, but got everything redone and reinstalled the head, but this time with a DW steel head gasket. Make sure your assembly area is surgically clean, use plenty of assembly grease and take your time. I've now driven my car for over four years, and about 15 thousand miles and knock wood, it's still holding together. 
Best of luck. If you want to "hear" the entire story, email me and let me know, lots of interesting mistakes, but I'm glad I did it myself. The engine needed the rebuild, it wasn't my choice just to do it, it had to be done, broken rings and scored cylinder walls. But it's not rocket science. 
Steven Kingsbury
BN1

On Apr 14, 2025, at 8:25 AM, warthodson--- via Healeys <healeys at autox.team.net> wrote:

I am preparing for the rebuild of my 100 engine & I need your help with a few questions. 
My intent is to build a strong/fast street drivable engine. The block will be bored out .020" to 0.30" over & will have a Welch "fast road cam".  I am planning on an aluminum head, steel crank & forged, light weight connecting rods. 
My first question is should I have the block boiled out & if I do will that require replacing the cam bearings?  I recall reading that they are not currently available. Is that still true?
I was planning on a compression ratio in the range of 9.0 to 9.5. I notice that some suppliers only offer 8.6 as their high compression offering. What is the reason for this? Is it standard practice today to use pistons with 3 rings? Where is a good domestic source for pistons?

Gary Hodson
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