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Old 09-23-2019, 04:33 PM   #1
mrlaser
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Default 8BA compression issues

I have been restoring a 1951 Ford Victoria for the past 6-8 years' The engine was rebuilt in a local machine shop 6 years ago. The engine sat unused until recently. It was in a dry, climate controlled building during this time. Every few months I added MMO to each cylinder and turned the motor over. The car has now been restored and placed on the frame. I have been unable to start the motor in spite of the fact that the carburetor, has been professionally rebuilt, the distributor ,which is NOS, has been set up on a Sun machine and the remainder of the ignition system is new. There is fuel coming from the accelerator pump and there is a good spark at the plugs when grounded on the block. The system is 6 volt and positive ground. The tdc was set by putting a rubber cork in #1 , turning the engine over until the cork popped. The pointer points at the bump on the crank pulley. When I did not get ant apparent firing, I decided to (belatedly since the engine was rebuilt) check the compression. All cylinders are 29-30 pounds. I am at a loss to explain this. I can understand that with the prolonged sitting some of the rings might have become stuck, but not all of them. BTW the engine was bored, the crank reground and the cam reground at a cam shop. New pistons,rings, bearings etc. Ideas.?
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Old 09-23-2019, 04:45 PM   #2
flatford8
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Default Re: 8BA compression issues

Prolonged running on an engine stand isn’t a good idea but, was this one ever run at all?..... Do you know if it ever had compression after the rebuild?.....try some type of penetrant and turn it over with the plugs in..... ark
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Old 09-23-2019, 04:51 PM   #3
Bob C
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Default Re: 8BA compression issues

Do a leak down test, that will tell you where you are losing your compression.


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Old 09-23-2019, 04:56 PM   #4
Kurt in NJ
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Default Re: 8BA compression issues

I have gotten compression back on engines that have been sitting and had debris on the valves causing low compression be using a air hose blowing air into the cylinder and cranking, I used the hose adapter that is used to put shop air into cylinder - then crank with starter----- this assumes that engine was put together correctly

Possibly the cam timing is off, look at valve position, when ex is just about closed, and intake is just starting to open the piston should be at top center--- easier done if car can be rolled in top gear
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Old 09-23-2019, 05:06 PM   #5
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Default Re: 8BA compression issues

Fuel coming from accelerator pump usually means the carb is flooding. Check for dirt in the fuel system and check the needle and seat. Common on first fire up to collect assembly dirt in the system.
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Old 09-23-2019, 08:46 PM   #6
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Default Re: 8BA compression issues

Thank you all for the suggestions. I plan to do a leak down test later this week. The noted fuel is only when the throttle is opened. I don't remember whether this engine was rebuilt with adjustable lifters. I had a second flathead built by H&H at that time and I am not sure which one had them. Would insufficient valve clearance be a possible cause? It seems that the nearly identical readings in all 8 cylinders would be awfully coincidental without some common problem.

Unfortunately, I have moved away from the area where the rebuild was done and lost most of the paperwork on the build. I plan on calling the shop to see whether they may have some records in their files re.the work done
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Old 09-23-2019, 08:49 PM   #7
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Default Re: 8BA compression issues

Also, the engine has never been started either in the car or on an engine stand.
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Old 09-24-2019, 07:03 AM   #8
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Default Re: 8BA compression issues

With all the cylinders being low and equal it might have a cam timing problem. If the leakdown shows little problem that is something to consider.
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Old 09-24-2019, 07:22 AM   #9
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Default Re: 8BA compression issues

I'd suspect your valves aren't fully closing.
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Old 09-24-2019, 09:43 AM   #10
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Default Re: 8BA compression issues

Fully, or partially stuck valves are pretty common on a flathead v8 that has sat for years. Both my 39 and 52 had zero compression on a few cylinders after a long rest and it took a little work to loosen them up before they would seat. Keeping the cylinders oiled is good but it won't get up to the valve area on a flathead.
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Old 09-25-2019, 07:42 AM   #11
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Default Re: 8BA compression issues

If you can easily hook up an air hose to your spark plug hole that will tell you everything. All you're looking for is where the air is escaping. If you hear it through the fill tube then it's rings. The carb is an intake valve and the exhaust will be coming out the pipe. Did you try oiling the cylinder with motor oil and redoing a compression check? I had a 70 chevy 6 cylinder I had to replace the head on due to a couple of cracks. It was running but I could not get it to start. Seems the coolant had washed down the cylinders and and there was no compression. A little oil in all the cylinders and it came to life. I imagine the rings were a bit worn also but it ran well enough.
Your rings have not been seated and even though you oiled them they may have dried out. Good luck.
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Old 09-25-2019, 03:40 PM   #12
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Default Re: 8BA compression issues

I just had a similar issue with a flathead 6 Continental on an air compressor when I went to sandblast my Model A body last month. The motor had sat unused for several years but was loose enough to turn easily by turning the fan by hand with the plugs in. Wouldn’t fire up for love nor money until I removed each plug and squirted a few pumps of motor oil in each cylinder with a pump can. Replaced the plugs and it fired and ran instantly. Smoky for the first few minutes but once it ran there was no issue again you could shut it off and restart it no problem. Give it a try you might get lucky like I did.
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Old 09-30-2019, 01:31 PM   #13
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Default Re: 8BA compression issues

I did a leak down test with disappointing results. All the cylinders except one were at 45-50% with the air leak coming from the carburetor. The remaining cylinder was 80% with air escaping from the carb and the exhaust pipe on that side. Next I plan to remove the intake and that followed by the heads if necessary. The engine has adjustable tapers so I wonder about the valve clearance.
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Old 09-30-2019, 02:44 PM   #14
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Default Re: 8BA compression issues

Have you verified that crank gear to cam gear is properly timed, per Kurt NJ suggestion?

Very unlikely that valve clearance is the problem on all 8 cylinders. Probably rusty valve stems causing sticking valves.
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Old 09-30-2019, 06:13 PM   #15
mrlaser
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Default Re: 8BA compression issues

The crank gear issue is still an unknown. I did speak with the engine builder who assures me that the marks on the cam and crank were aligned. I have had a limited amount of time to work on the problem and garage temperatures near 100 haven't been conducive to my productivity.

Re: the valve clearance, in view of the fact that all of the cylinder compression readings are 40 ((except one at 20) I just wonder whether a small error in the valve clearance might prevent complete closing. Obviously, the one outlier is likely stuck as well.
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Old 09-30-2019, 06:28 PM   #16
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Default Re: 8BA compression issues

When you check the timing marks make sure someone didn't add their own set of marks on the gears , I seen this happen when a person un familiar with the engine tried to do the right thing and put their own witness marks on the crank gear, thus creating a problem for a later rebuild. the crankshaft keyway will be at approx. 10 o clock when the cam and crank gears are aligned together.
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Old 09-30-2019, 07:03 PM   #17
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Default Re: 8BA compression issues

When you pull the intake and check the valve clearance you should know more about stuck valves. If valves are stuck the clearances should be more than spec.
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Old 09-30-2019, 08:24 PM   #18
mrlaser
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Default Re: 8BA compression issues

Thank you all for the suggestions.
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Old 10-01-2019, 04:50 PM   #19
Kurt in NJ
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Default Re: 8BA compression issues

Have you tried blowing compressed air into the cylinders while cranking, this I have found blows debris out of the valve seating area, I have used this to get compression back in several engines that have been sitting
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Old 10-03-2019, 06:07 AM   #20
mrlaser
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Default Re: 8BA compression issues

I have not, but will before taking the disassembly step. It had been mentioned before but I forgot to try the suggestion. What kind of pressure do you suggest? Thanks again to everyone.
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