Weber - gas coming out of 1 throat

[2cams70]

But it is interesting that the leak is in the same cyl that had the lowest compression previously, fwiw.

5 psi variance between highest and lowest reading cylinders is not enough to cause a rough running issue in my opinion. It's well within the tolerance range of measurement accuracy. That result may no longer have proper meaning of course because the head has been off and on in the meantime.

You say you've checked ignition - by that I assume you mean you've checked firing order, spark strength at each plug, static timing, dynamic timing (i.e checking that timing advances with increased speed). I'd be crossing off compression too assuming you didn't upset anything by removing and replacing the head.

That leads us back to fuel. You don't need to rip the engine out to fix a fuel issue.

[512BB]

'once contaminated with oil are virtually impossible to get clean enough to repair by adhesive or welding'

That just is not the case. I have lost count of the number of ali diff housings that I have had welded up due to cracks and other damage, and they don't come much more oily than one of those. All turned out perfectly and have been reused. You just have to take what ever you need welding to someone who knows what they are doing. Full stop.

Leslie

[2cams70]

'once contaminated with oil are virtually impossible to get clean enough to repair by adhesive or welding'

That just is not the case. I have lost count of the number of ali diff housings that I have had welded up due to cracks and other damage, and they don't come much more oily than one of those. All turned out perfectly and have been reused. You just have to take what ever you need welding to someone who knows what they are doing. Full stop.

Leslie

Not sure what this is about. Are you responding to the wrong post???

[RichardHawkins]

2 cams,

I think Leslie is responding to my comment about the difficulty of repairing cracked and oil contaminated castings that may have porosity.

Richard Hawkins

[steve lyle]

Today's update. With the head off, I sent pics of the head and block to Barry (the head guy) and Ken (the parts guy). Barry id'd where he thinks the coolant leak is - the passage between cyl 1 & 2 has a bit of roughness there, so we'll skim the head to remove it. He also asked that the head be pressure tested, so that will happen too.

Maybe the bigger issue is the oil on top of the pistons and seeping in front of #1 and behind #4. And the fact that the cylinder walls are mirror smooth after about 100 miles. Barry thinks the hone wasn't appropriate for the rings, so I'm working with Ken and the machine shop on that. Ken's a bit mystified, because he's sold a lot of these rings without seeing this issue, so I asked him to call Barry to discuss. As for the hone, the machinist who worked the block has retired, and isn't returning calls from the shop. So while they they have confidence he did it to spec, they can't prove it and it sounds like we'll never know exactly what he did.

I'll pull the #4 piston and take some pics and send those on, but it sounds likely that we'll replace the rings and rehone, so the entire engine will be coming apart for that.

I was concerned about finding the crack in the front cover. Nothing to worry about there, as soon as I got the front cover and damper off, the crack was visible. I found a shop in town that thinks they can weld that up, so I'll take it to them tomorrow.

The clamp ring on my 25D is cracked, making it difficult to clamp in place as firmly as I'd like. It turns out that Advanced Distributors has a service where they machine off that ring, and press on a solid steel ring, pinned in place so it can't move, and thick enough where it's essentially uncrushable. So the distributor got sent out today for that fix.

IMO, the oil on the surface of the gasket, and the coolant leak, indicate insufficient clamping, which Ken agrees with. I'm using ATP head bolts. Ken had me check to make sure they weren't bottoming out. So far I've checked one, which wa .2" short of bottoming out, so no problem there. I'm guessing the others are the same, but I'll check them, too. When the head goes back on, he suggested spraying the gasket with Copper Note, and torquing to 70 ft-lbs as well.

So, several threads in progress addressing various issues or possible issues. And who knows what else is out there - certainly a fuel issue of some sort is still a possibility as well.

The crack in the front cover

The block immediately after head removal

The head immediately after removal

[gjz30075]

Good update, Steve. Any more info on Advanced Distributors? I just get HVAC places on my searches.

[2cams70]

The bores could be “mirror smooth” as a result of the fuel mixtures being way too rich and therefore the fuel washing the lubricant off the cylinder walls. How do the bores look below the piston where the rings don’t travel? Are the honing marks still there?

Your primary problem seems to be fuel mixtures. You need to get that right first. If you don’t get that right further things can be damaged as a consequence - except for the distributor base and front cover crack of course. Those 2 issues are just down to either insufficient knowledge or negligence.The front cover crack is due to over tightening of the front cover to head through bolts and likewise the distributor crack is due to clamp bolt over tightening. It’s well worth investing in good quality torque wrenches and screwdrivers. In my box of weapons I have torque screwdrivers 0.3 to 1.5Nm, 0.6 - 3.0Nm, 1.2 - 6Nm. Torque wrenches 3.0 to 24Nm, 15 - 160Nm, 20 - 270Nm. Good quality torque measurement tools are worth their weight in gold.

No doubt that front cover crack is due to someone in the past noticing an oil leak in that area and deciding to tighten that bolt up a wee bit to try and stop it - “OK here goes, oops!” That bolt as it is tightened practically tries to pull the head towards the cover over thin air as the cork gasket underneath is a lot more compressible than the surrounding head gasket. It, the similar bolt on the other side and the middle bolt under the cam cover must not be over tightened or you risk this happening.

[steve lyle]

Good update, Steve. Any more info on Advanced Distributors? I just get HVAC places on my searches.

Here ya go...

https://www.advanceddistributors.com/

AD is owned by Jeff Schwemmer, who posted a lot on the MGB Experience site when I was rebuilding my B. He rebuilt the distributor for that car.. I've seen his ads in classic car mags as well. Highly recommended.

[nmauduit]

...
the fact that the cylinder walls are mirror smooth after about 100 miles.
...

that in itself (whether from lack of or improper honing, or indeed rapid glazing) would not cause the engine "running rough" if the bores are all dimensionnally within specs for the pistons, it would only affect long term reliability (oil consumption to be monitored).

[steve lyle]

Picked the head up from the machine shop today. They milled .007" off - said it was warped diagonally. On the good news front, it passed the pressure test.

Barry wants me to replace the JE top ring with one from Total Seal - I just ordered a set, getting the gapless version.

I dropped the front cover off at the weld shop yesterday - he's pretty certain he can fix it.

Distributor got shipped out yesterday as well.

I disassembled the rest of the block today. I'll take in in tomorrow for rehoning - Barry wants a 280 grit hone. I've got gaskets coming from Ken.

On Friday we leave for a week tour of Normandy - really looking fwd to it. Most parts should be here when I get back, so the reassembly can begin. I'm guessing the distributor is the long pole - there's a bit of a backup there. But the engine can go back in without it if it comes to that.

[2cams70]

When you do get it going again and provided it isn’t squirting fuel everywhere drive it straight to the nearest reputable place capable of putting the car on a dyno for fine tuning of the ignition and fuel calibrations. You’ll save yourself a lot of grief, time and heartache. Sounds like you have a lot of friends with equipment. Surely one of them has a dyno. 151’s are supplied with a generic calibration only and will need fine tuning to suit the specific engine they are fitted to. This is best done on a dyno and despite what some people may say (particularly the ones selling them) not just an AFR mixture reader.

[alan.barker]

Hi Steve,
Enjoy Normandy pity only for a week.
We will be for a week Cote d'Amour st Brieuc. We live in Morbihan
Alan

[steve lyle]

Here's an update covering the last couple of months.

Yes, one week in Normandy isn't enough. We got more of a 'sampler' tour, so we'll know where to stay and what to see in more depth next time. I would wish that every American have a chance to visit Normandy - it's quite the experience, even if only for a week.

On to the car. I got right to picking up the cover, block, etc. - all were ready when I got back. Within a couple of days the distributor was back, and the rings arrived - gapless from Total seal.

Assembly took a bit of a delay when it turned out the lady in the row behind us on the plane home wasn't coughing from a cold - so the wife and I went through another Covid spell.

Reassembly went smoothly - you actually get more efficient at this the more times you do it.

Initial tests showed that the oil leak was fixed. A leak down test showed the coolant leak was solved. An inspection after my spirited 8 mile test loop drive, which always showed gas in the airbox previously, was dry this time.

But the roughness on acceleration remains. The degree of roughness is proportional to the aggressiveness of the acceleration. No spitting or backfiring. I wouldn't describe it as a stumble or dead spot. It almost sounds like an exhaust leak, but I tried a test with the exhaust pipe off and no change. It's like a staccato feeling, as if one cylinder isn't fully participating.

I reached out to Tim, who hooked me up with Chris - who's got a shop in Oklahoma City that preps vintage racers, among other things, who suggested I check the strobe on a timing light at higher revs. Which I did, and it seemed to go a bit erratic above 3k or so. So I called Jeff S., who rebuilt the distributor - he recommended solid core plug leads and non-resistant plugs, check the coil, points, etc.. So I ordered new wires and all new ignition parts from DBE, and stole the coil and BP6ES plugs, no longer available in the US, from my MGB. With all that, the strobe looks good, roughness decreased maybe a little, but is still definitely there. All at the cost of radio interference, but I think we can eliminate ignition as the ultimate problem.

I had welded a bung in the exhaust for my AFR meter. It shows about 12.5 at idle, dropping to 10-11 on acceleration, and when cruising at speed - around 3000 RPM in 5th, about 65 -70 mph. But of course that's an average of the 4 cyl's, so the problem could be a single throat problem of some sort. A bit rich,

So the investigation continues - I'll reach out to Chris again - it sounds like he gets to Tulsa periodically, so maybe he can see it/drive it for himself.

That said, I think it's at the point where I'm willing to drive it, even to LOG in 5 weeks, and to OKC to put it in Chris's shop if he thinks that's necessary.

I'll keep you posted.