Rebuilding the 4.2 engine from my 1971 2=2. My question concerns the rope seal rear crankshaft. Is the new seal generous in length, or should I keep pressing it into the groove until it does not need to be trimmed?
Thanks
Mike
Hello Mike,
My math always resulted in =4. 
However, with regards to the seal, original seals (no longer available) were the correct length and should protrude from each end of the groove in each of the mating parts, a equal, small amount. This was so a seal was achieved at the ends of the two part seal. Care needed to be taken that no material was trapped between the housings that contained the seal.
Most, if not all of the seals being supplied today are way too long and have to be cut to length. Each half of the seal should be well and truly pressed into the groove so that they fill the void completely. I then use a piece of 0.010" shim with a notch cut the same profile as the groove, so that it fits around the seal protruding above the face of the housing, then a new, sharp raver blade to trim the seal a uniform distance above the face of the housing.
Regards,
Bill
1 Like
As usual Bill is correct, I might add that it is a good idea to assemble and then remove the cap and inspect if any of the fibers have been caught between the block and the bearing cap. Trim off any caught fibers, as you don’t want to have the bearing cap on cocked.
The same method I used. I only add that I used a small daub of RTV on the rope ends, and a wee fillet on the longitudinal chamfer of the main cap.
Glad to see corroboration of the technique, for which many have derided me for doing.
1 Like
I‘ve since watched tens of videos and seen dozens of posts and they all agree that they have to be trimmed, most say to hammer them flat, move them so they’re more flexible, some use sealer in the groove, some hammer it with a chisel so it doesn’t turn, some use tools and some the crank itself. All leave the seal a hair proud and cut off the fibers after checking is a good plan.
Grease on the rope and sealer on the mating surfaces, give the crank one last spin.
The one I installed myself has not leaked in the whopping 30 minutes it’s been running so far and I do hope it stays this way.
We went mad trying to hammer in the first seal, I‘m sure @wiggles remembers. 
1 Like
Great minds think alike Paul. 
Regards,
Bill
1 Like
Are you referring to the =4 Bill? 
Regards,
Bill
1 Like
Thankyou all. It’s a long way off running, but I just hope I live long enough to see it and report back!!
Regards
Mike
1 Like
I spent a long time pounding and pushing and fitting my rope seal and she still leaks a quart every 400 miles or so.
LLoyd
It’s not what you look at that matters. It’s what you see.
Henry David Thoreau
I always read that the rope seal comes the right length and one should never trim it
The wise (now retired) Jag mechanics here in Vancouver who used to work at the Jag factory assembling E-Types long ago told me that you work the seal until it fits both halves and then use the sizing tool, after putting graphite grease on the running surface
Then take apart, take out the two half rope seals, put little dabs of sealant in each goove (which will stop it rotating), then ropes seal halves back in, then put graphite grease on the rope seal running surfaces, then a little dab of sealant on the parts of the seal that mate with the other seal part when it is assembled. Then put crank in. Then put bearing cap on and tighten
Dennis 69 OTS
2 Likes
That used to be. But not anymore. I‘ve seen 3 different seals now and they were all over ½“ too long when fully inserted, or put next to the old rope… they will not fit by a lot. You roll in the seal with something suitable, then you hammer it in starting with a large nut or something comparable, then use the crankshaft (or the tool if you have to, same diameter), then cut. Same on the other half. It needs to be cut. It would be obvious if there was a way to make it fit.
1 Like
At some point, they did: I guarantee that some later ones were entirely too long, like a 1/4", each end.
That was consistent with other rope-sealed engines, like Austin, Triumph, and others.
That tells you how long ago I did my last rope seals
Thanks
Denny
You’re lucky.
I found a few nos gasket sets from the early 70s on ebay today. They might fit.
Does this mean that you do not use the factory sizing tool Bill?
No need (Even though I have access to a copy of the tool), @Wiggles did billions of engines using the crank, @DouglasBuchan (IIRC) says they measure the same and YouTube does it too. I think the crankshaft works great.
Not quite billions…
I always thought that the sizing tool was slightly less diameter than the crankshaft. Does anyone know? After all, it is used for undersized cranks
Dennis 69 OTS
Hello Geoff,
I use my own factory grown version of the factory tool. It has multiple sleeves with incremental increase in OD that fit on a common shaft. It allows the rope seal halves to be gradually pressed home, keeping the ID of the seal concentric with the centre line of the main bearing journals. One half at a time is done until the second last sizing sleeve is used, at which time, the ends are trimmed to length as described in my earlier Post.
Many have success using the crank shaft to size the seal, My opinion is that the seal can end up a little tight initially using that method and too tight a fit can lead to overheating; nothing kills the rope seal quicker than excessive heat. I also find using a sizing tool more convenient than the crank shaft.
Regards,
Bill.
1 Like
Hello Dennis,
I’ve measured the Rope Seal journal of the crank shaft from 3.119" to 3.1255" and its my understanding that the design size of the factory tool is 3.119".
I’ve found that there is quite an amount of spring in the compression of the seal and sizing it using a tool the same as the actual crank can result in the fit being initially too tight on the crank shaft journal.
Regards,
Bill