Symptoms of Stuck Valve ???

[dklawson]

The question pertains to the 1275 transverse engine in my Mini but I think there's more information to be had here among the inline Spridget owners so I'm posting here.

Yesterday I started my car to drive home from work and it fired right up. It was running fine with minimal choke. After less than 1/4 mile the car bucked, stumbled and lost power. The symptoms indicated to me that for some reason I'd lost one or two cylinders.

I pushed the choke in thinking I might have fouled a plug and assumed it would clear up. After a mile there was no improvement so I turned back to the office where I pulled the plugs to install my backup set. The old plugs looked fine. There were no heavy deposits and no carbon tracks that might have caused the problem. The plug wires are fairly new as is the cap and rotor.

After installing the new plugs the car seemed to have the same problem... barely running with a rough idle and fump, fump, fump noises through the exhaust. I was going to call AAA for a flatbed when I decided to give it one more try. The car started and was behaving normally. I drove around the parking area and there were no more stumbles or anything. I borrowed a friend's cell phone, made sure my tools were at the ready and started the 25 mile drive home. The car ran like a top the entire way.

So... any suggestions on what to look for? The only thing I could think of is that I've got a tight valve that may have stuck open until the head warmed up a bit. I'm open to suggestions and would like some ideas for where to look next time this happens. I doubt I'll tear the car apart looking for this problem. Hopefully armed with your suggestions I'll know where to look when and if it happens again.

 

[Trevor Jessie]

I was thinking plug wires/cap. Did you check the inside of the cap for condensation?

 

[dklawson]

Thanks. It was 5:00 p.m. with an ambient temp close to 75F and low humidity. Condensation never crossed my mind.

I have a Hitachi dizzy with Nissan cap and rotor installed on the car. The electric tach appeared to be working normally apart from the expected fluctuations as the engine's RPM stumbled. (It wasn't shooting up and down off of zero RPM... which indicates that at least the coil was firing). I think I'll change the plugs, cap, and rotor as insurance... but I'm not sure they're at fault.

I was running Bosch W7DTC plugs. Those are fancy plugs for VWs that an Austin-America friend of mine endorses. I've had them fail before so I was considering going back to NGK plugs. What's the preferred NGK plug for big-bore A-series engines?

 

[ChrisS]

NGK BP7ES or BP6ES. The 6 is hotter than the 7 (NGK is backwards of most with their heat range numbers). They may be sold as BPR#ES for resistor plugs, I can't remember.

 

[Morris]

I had a reoccuring stuck valve on my 1500 (thanks to a crappy machine shop). It had the exact same symptoms you describe. I would pull the car over, tap the valve free with a small hammer, or work it free using a screw driver as a lever. Sometimes the valve would not bother me again for a week. Sometimes it would stick again on the same trip. Occassionally it would just fix itself.

However, I will say that when my valve stuck, the car was nearly undriveable.

 

[DrEntropy]

Just for S&G do a comp check while you're in there, or if you have the rig, a leakdown test.

I get a crossover ref from N7Y Champs to the NGK BP7ES here.

The Bosch plugs and British cars seem incompatable to me for some odd reason. and Alfas run great with 'em... go figger. <shrugs>

 

[dklawson]

I'll get a set of the BP7ES plugs and give them a try.

Again, based on how the removed plugs looked, I doubt they were to blame. The car has done this once before. I'm hesitant to blame this on any machining work... there are probably 3000 miles on the engine since its rebuild which included a re-worked 12G940 head. However, my thought was that somehow one or more valves heated up very quickly and stuck in their guides. After the rest of the head warmed up and the guides opened a bit... perhaps the valves were freed, giving me back normal operation.

Does anyone else have any experience with what a stuck valve's symptoms are so I can compare? Even if it's a sticking valve I may not do anything. I probably will just limit my use of the car to "around town" for the next year until things loosen up a bit more.

EDIT: Sorry DR., I meant to address your suggestions. I thought about compression or leak-down tests but I suspect that as the car is now (normal) the tests wouldn't reveal anything. I anticipate that I'd need to run those tests when the problem presents itself again... which probably won't be when I have access to my tools.

 

[racingenglishcars]

I have had either a stuck valve or a piece of dirt stuck in the valve seat, which cleared up spontaniously. Very similar symptoms.

I have also had a piece of dirt in the spark plug gap, but that would go away with a plug change

With 75F and low humidity, condensation is probably not the problem. Though arcing through dirt could cause something.

Since it started running smoothly afterwards, your compression is probably good.

My guess, dirt in the valve. (or a broken screw from the carb)

 

[regularman]

If it happens again, try to identify the missing cylinder. The quickest way it to remove the plug leads one at a time, either while running or shut if of unhook one and restart. I know its a pain on the mini to do this and not get shocked. Does the distributor have points and condenser. That sounds kind of like what a condenser might do but the cylinder missing will be random.

 

[regularman]

Oh, and all my stuck valves became bent valves.

 

[cdsmith]

Don't know if this helps, but when the valve stuck on my 1275 I had some serious blow-back through the carbs...
Intake valve was stuck open... The engine ran, but real rough...
If it does it again maybe pull the valve cover off and take a look at the valve train...
cd

 

[regularman]

It might be worth draining the coolant and unbolting the intake and exhaust manifold and pulling the head. If its been a while I would pull each valve and put in a new valve seal and use a drill and some lapping compound and lap each valve to make sure it seats well and clean any carbon out as well. Top end gasket sets are dirt cheap,20 bucks or so.

 

[regularman]

Wait, I'm trying to think which kind you have. Which way is the motor turned? The old ones had he carb to the back and the dist to the front and then they changed it around. The old ones with the 10 inch tires were bad for the plug wires and cap to get wet and do all kinds of crazy things. I'm thinking that was mostly the 950, then they lowered the engine to 850 (The 950 would fly)and then 1000 and 1100 and then 1275 and then whatever came after that. If yours is a 64(saw that in your picture) then the 1275 is not original but what about the driveline? With the Distributor near the grill, I would suspect a wire. Also, my comments about pulling the head may not be accurate. I have pulled mini engine heads and worked on them in parking lots under tarps to get out of the rain,so they are not that hard but might be more involved than a sprite or midget, but the top end of all the motors ws pretty much all the same.

 

[dklawson]

Regularman, thanks for the suggestions. The 1275 is original to my -S. It's one of the first 500 1275 engines built. The 948 was exclusive to inline applications. All the transverse engines have the dizzys in the front (apart from the very last injected engines), right behind the grille so the wires are easy to get to.

The head is a low mileage professional rebuild from Seven. I'm not ready to pull the head off to search for the problem quite yet. There should be little or no carbon or build up as there's probably less than 3000 miles on the rebuilt engine.

The car has a vacuum gauge and once the problem righted itself there was no indication via the gauge that the valves were doing anything out of the ordinary. My idle vacuum readings are high and steady which imply that no damage such as bent valves has occurred. It also implies that they are once again closing properly.

For the time being I think my approach is going to be to limit my use of the car to local drives around home and to allow the car to idle and warm for a couple of minutes before taking off. The car has done this one time before, perhaps nine or ten months ago. The only obvious similarity was that both incidents occurred literally within a minute of starting the engine.

 

[Hap Waldrop]

The most common reason for a valve to to stick in a guide is not enough guide to stem clearence, bronze guides, which is more than likely what you have if you got Seven to rework your head take more clearence than stock guides, but Seven been around long enough to know this and I doubt it's the problem. You could pull the plug wires and plugs and turn the engine over with the starter with the valve cover remove and look at the valvetrain to see if you see anything that doesn't look right. If your valves do stick in the guides, as mentioned above, they stand a good chance of getting bent, which then can quickly lead to more problems, broken rocker arms, damge piston/s, bent pushrods, even a wiped out cam lobe, so hopefully that's not your problem.

 

[Morris]

I would try to recreate the conditions of the stickage so you can jump out, pull the valve cover and collect some conclusive evidence of whether or not the problem is a stuck valve.

If you know how to prevent those conditions, you don't necessarily have to pull the head right away, but at least you confidently know what the issue is so it can be repaired at your leisure.

 

[regularman]

Ah, you have the S. I don't think I have ever seen one of those. All I ever saw were austins and very old Morris minis. There was some really old minis with the door hinges on the outside and 10 inch tires that had the first 950 engine and it was different from the rest. I distinctly remember having to reach my hand back in the nether regions of the plug wires to get to the distributor and adjust timing without getting shocked. Of course, I have no way of knowing if this was stock, cause all we had was junkers. We were in the unique position of being able to "use and abuse" minis that were too rusted out to pass MOT inspection and were headed for the crushers. Looks like you spent a lot of money on that head. No need for me to give you the quick and dirty way to straighten bent valves /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

 

[dklawson]

Thanks Hap. This head has cast iron guides.

I think my approach at this point will be as I mentioned to limit my use to local driving for a while and keep my eye on the vacuum gauge. I clearly haven't bent a valve yet and obviously I'd like to keep it that way. Since the only times this has happened have been far between each other and only immediately after starting a cold engine, I'm going to allow a few moments of idle time before driving off and be prepared to search for the problem when and if it occurs again.

Thanks to all who replied to this thread.

Edit: Regularman, I've never heard of a 950 Mini. The only 948s I'd heard of were the inlines for the Spridgets. That doesn't mean someone didn't get creative with a transplant though. The -S wasn't unique, it was sold in both Austin and Morris models up until those names were dropped during the BL period to simply refer to the car as "Mini". Mine's a Morris with the external hinges and the 10" rims as you mentioned. The basic mini started with the 850, then there was the 997 Cooper, the 998 Cooper, 970 Cooper-S, 1071 Cooper-S, and the 1275 Cooper-S. The 998 engine became the most common for most "standard" Minis.

 

[dklawson]

Conclusion:
Thanks for all the suggestions. I may have the answer to my problem.

I checked the leak-down values and was going through the ignition checks without finding any problems.

When my problem first started I checked to make sure I was getting fuel BUT I only looked at the level of the fuel in the "back" carb's bowl. I don't know what possessed me to check today but I took the cover off the front bowl and discovered it was empty. A little bit of work to free the needle valve and the car fired up normally and immediately settled in to its normal idle.

So... I had a valve problem... just not in the cylinder head. The rub is that I had recently replaced those fancy Grose Jets with regular rubber tipped needle valves because my Grose Jets appeared to be leaking. Darned if you do, darned if you don't. Too much fuel, then not enough.

Next time I'll take a look at both bowls before doing such extensive tests. I suppose the main reason I didn't start with fuel as the potential problem is the car didn't exhibit the lean, backfire through the carb, symptoms that I've seen on other cars with blocked fuel delivery.

 

[DrEntropy]

We all tend to "OverTech" things. It usually ends up bein' "TheDumbStuff" as the cause. To look at it Half-Full: you now have a baseline from which to eval your rebuild!

...as long as you remember to:

A) Write it all down.

B) Remember where ya put the info the NEXT time you do it!

/bcforum/images/%%GRAEMLIN_URL%%/jester.gif