Spitfire Compression Test - Spit 1500

As you can see... 100psi, 70psi, 95psi, 100psi... and the pic of the plug is from the one that was the lowest (the others were perfect). Each check was 8 revolutions (but leveled off at 4).

Since only 1 was low, its not the head gasket, and since I'm blowing oil out of my dipstick hole, I can only assume its my rings and not valves. I didn't do the 30wt oil-in-chamber check as my battery was running low, and that would only confirm/deny the rings vs valves.


So what now? Is this still OK enough to drive to the car show in 2 weeks or will I likely blow my head gasket or worse?

I'd do the oil-in-chamber check to be more sure, but you're probably right that it's rings. Probably ok to keep driving, so long as you keep your eye on oil level and pressure, etc. But it's probably overhaul time. (Not even that hard to do while the engine remains in the car, so long as you don't require a rebore!)

Having just one cylinder low causes me to think that it just might be a valve problem, either one stuck and not closing or one burned and cannot seal.
A check with a Vacuum Gauge could be of great assitance in knowing what to expect before a tear down.
I had a low compression reading on one of the cylinders when I got my TR6, about 25 #'s lower than the rest, and some spirited driving with detergent added to the gas cleared that up in a few weeks. The valve was apparently prevented from closing due to a carbon buildup. Here's a link for interpreting Vacuum Gauge readingss. You'll see how a valve problem can be diagnosed. As for the oil blowing up the dipstick, yeah it could be blowby or just a problem with your crankcase/ valve cover ventillation; been there, too.
https://www.users.bigpond.com/ergoff/vac1.htm

Andrew Mace said:

I'd do the oil-in-chamber check to be more sure, but you're probably right that it's rings. Probably ok to keep driving, so long as you keep your eye on oil level and pressure, etc. But it's probably overhaul time. (Not even that hard to do while the engine remains in the car, so long as you don't require a rebore!)

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When I get some regular non synthetic 30wt I'll try it (every bit of oil in my garage is Amsoil... even the drops on the floor), but I'm pretty sure I'll get the results of my guess. I'm not burning any oil though... not even on a cold start.

I used to use ATF in the carbs when trying to unstick a valve or ring with the old aircooled bugs... think this is worth a shot on this engine?

poolboy said:

Having just one cylinder low causes me to think that it just might be a valve problem, either one stuck and not closing or one burned and cannot seal.
A check with a Vacuum Gauge could be of great assitance in knowing what to expect before a tear down.
I had a low compression reading on one of the cylinders when I got my TR6, about 25 #'s lower than the rest, and some spirited driving with detergent added to the gas cleared that up in a few weeks. The valve was apparently prevented from closing due to a carbon buildup. Here's a link for interpreting Vacuum Gauge readingss. You'll see how a valve problem can be diagnosed. As for the oil blowing up the dipstick, yeah it could be blowby or just a problem with your crankcase/ valve cover ventillation; been there, too.

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I tried the spirited driving today with no change. I don't have any detergent, so what should I get?

I don't have a vacuum gauge either, so a link to what kind I should get would be quite helpful.

Can I replace rings on this engine without pulling it? I'm thinking maybe so if a ring compressor will fit flush from the under side and clear the crank. I've only ever done rings from the top.

As for crankcase ventilation... Its clean and clear. I had the rocker cover off when I repainted it, replaced the hose, and have a new PVC tube into my new K&N Air cleaner. It works just fine.

Chemtool B-12 is a good detergent as is Techron, but don't expect "overnight " results. It took a couple of weeks driving some every day to break-up the deposit I had. You can find the gas detergents at places like Advanced Auto, Autozone, O'Rieleys and Walmart.
The Vacuum Gauge at the first 3 I mentioned for about 30 dollars.
You can push the pistons out of the top, like you did in the past, after you drop the pan and take the rods loose from the crank.

"Can I replace rings on this engine without pulling it? I'm thinking maybe so if a ring compressor will fit flush from the under side and clear the crank. I've only ever done rings from the top. "

And thats the only way you will ever do it.

Pull head and pan, remove the rod cap(s), push the piston(s) out of the cylinder. Don't mix up the rod caps.
Check the top of the cylinder for ring wear. This will be a lip at the top of the cylinder. If there is one, you must first remove it (there is a tool for doing this, not expensive) or the piston rings will hang on the lip.
Clean the piston, esp the ring lands. Install new rings with the gaps offset from one another. Clean up the cylinder with a hone, being sure to cover the crank journals to protect them from debris caused by the honing. Blow out with compressed air and wipe the cylinder to remove what ever the air didn't remove. Apply oil or assembly lube to the pistons, rings, and cylinder bore. Reinstall piston using a ring compressor.
You might want to replace the rod bearings while you're there. Mains too, if you've got the time.
Reassembly from here is the reverse blah, blah, blah.

I'd look at the valves first though, as they(it) can can cause the same type of problems that you are experiencing. You might try misting some water into the carbs using a spray bottle while the engine is running. This will usually knock carbon build up off of the valves and piston tops.
Hope this helps.

bgbassplyr said:

You might try misting some water into the carbs using a spray bottle while the engine is running. This will usually knock carbon build up off of the valves and piston tops.
Hope this helps.

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Water eh? This is new to me. Is it at idle or when goosing it like the old ATF trick? (Again, will the old ATF trick even work on these?)

Sorry if I missed this - but have you adjusted the valves recently?

Ok, after adjusting the valves. PLEASE remove ALL spark plugs when performing a compression test.....


Good idea to remove an ignition supply wire(primary lead to the coil). I also recommend blocking open the throttle. Then crank the engine 5-6 cycles on each cylinder......

Wow... the "water trick"... been awhile since I've heard of that being used. Way back when, a mechanic taught me how to do that with my old college beater car, that was always carbon fouling the plugs... just use to pour water down the carb intake while idling... just not too much too fast or the engine would stall. Blip the throttle a few times to clear things out, and done. Made the plugs squeaky clean...

But let's not forget that 70 psi on #2. That's not carbon fouling; that's a piston or valve that isn't sealing. Combined with the blowing oil, it's almost certainly a piston problem.

To answer the original question, probably it will be OK to drive it to the car show that way. If the piston or cylinder wall are going to get damaged, most likely they already are damaged.

But it is at least possible that you are looking at a broken piston, which means there are pieces that might get loose into the crankcase and make a significantly worse mess than you have now. So the question you have to ask yourself is "Do I feel lucky?".

TR3driver said:

So the question you have to ask yourself is "Do I feel lucky?".

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Indeed I do!

So this Water Trick... Technique, mist or pour SLOWLY? And when, Idle, Mid RPM, Goosed?

Mist at RPM. 3K and introduce it. Be prepared to "goose" the throttle as you do. Don't get goofy either... a few squirts and go to the other throat. Then drive it and check things again.

ISTR that back in the middle 50's there was a water injection system the hot rodders used for more power when drag racing. Only for shot bursts, not full time. Made a nice white cloud out the tail pipe, too.

And in 1962, Oldsmobile introduced the F-85 Jetfire. A 215 CI aluminum turbocharged V8 with a water/alcohol "injection" system that allowed a 10.25:1 CR.

Water injection has been around much longer than that, at least since the 30's. WWII aircraft used it for more power on available fuel. You see a lot of it at tractor pulls and so on, too (it even works for diesels). For example, the article at https://www.dieselpowermag.com/features/trucks/0607dp_diesel_smoker_tractor_pulling/puller_stats.html talks about using several gallons of water in just a 12 second run.

Somewhat amusing article at https://www.rbracing-rsr.com/waterinjection.html with links to some of the papers done way back in the 40's.

BTW, some may not know, that all-aluminum V8 (which was also used by Buick and Pontiac, tho without the supercharging & water injection) is the direct ancestor of the original engine in the Triumph TR8. GM didn't have very good luck with it (kind of small for those giant full-size cars, and people frequently overlooked refilling the "power fluid") and so sold the design & tooling to Rover back when. Rover has been developing it all these years, and just finally halted production just a few years ago now.

TR3driver said:

BTW, some may not know, that all-aluminum V8 (which was also used by Buick and Pontiac, tho without the supercharging & water injection) is the direct ancestor of the original engine in the Triumph TR8. GM didn't have very good luck with it (kind of small for those giant full-size cars, and people frequently overlooked refilling the "power fluid")

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...and possibly of interest... The biggest problem GM had with that engine was cost... it actually sold well, but the scrap costs caused by casting issues in block production were high. Also, in service, corrosion problems cropped up due to reactions between the antifreeze formulations of the day and the aluminum block / heads... A lesson that British Leyland and Stag owners re-learned years later with Triumph's internally developed V8...

jjw said:

Also, in service, corrosion problems cropped up due to reactions between the antifreeze formulations of the day and the aluminum block / heads... A lesson that British Leyland and Stag owners re-learned years later with Triumph's internally developed V8...

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Not so much the formulations available IMO, but the need to replace them every few years, which most Americans ignored until it was too late. Even TR3s have aluminum bolted to cast iron, which will corrode badly if the antifreeze isn't kept changed.

I was just thinking (harmful to my health, I know)...

Is it possible that my motor oil is too thin?

It wasn't leaking or anything till I changed to Amsoil 5w30 XL. Only reason I used it is because I couldn't get a definitive answer on the weight of the oil to use, and I had a full case of it as a mistake order for my Honda (uses Amsoil 5w20 XL).

Also, I haven't had the time to try the water trick yet, but when I try it, I'll post results.

UH, Yea.