The Ford Barn

alexiskai · 04-04-2020, 11:48 PM

This is a '29 coupe that runs a little poorly at low RPMs. I've been through all the carb and intake tests, those are fine. Timing is correct. So I started running tests on the cylinders.

A vacuum test indicated "worn/loose valve guides." A compression test showed 60-65 psi on all cylinders except for cylinder 2, which showed 40 psi on a dry test and 45 on a wet test.

To do the test, I cranked each piston to TDC in turn. I used an OTC 5609 cylinder leak tester. The compressor was set to 90 psi, but I never actually dialed the gauge up to full pressure because all four cylinders leaked 50% or more. All 4 cylinders showed hissing in the crankcase. Cylinder 2 also showed hissing in the exhaust. No hissing heard in the carb or bubbles in the radiator.

Assuming I did the test right, my guess is that all 4 cylinders are just worn after 90 years of use. I don't think the engine has ever been rebuilt, certainly not to the extent of installing oversized pistons. So presumably the rings are not sealing well? Is there any repair for this other than a rebuild?

The exhaust on cylinder 2 – I assume this is a burnt exhaust valve? Is that something I could repair without replacing the valve? Could I pull the head and clean up the valve seat or something?

The car does still run, so despite the clear problems with the pistons I may elect not to fix them if I can fix the symptom of poor running at low RPM.

Thanks for any suggestions.

04-04-2020, 11:48 PM	#1
alexiskai Senior Member Join Date: Apr 2018 Location: Mebane NC Posts: 2,848	Comments on these leak-down test results This is a '29 coupe that runs a little poorly at low RPMs. I've been through all the carb and intake tests, those are fine. Timing is correct. So I started running tests on the cylinders. A vacuum test indicated "worn/loose valve guides." A compression test showed 60-65 psi on all cylinders except for cylinder 2, which showed 40 psi on a dry test and 45 on a wet test. To do the test, I cranked each piston to TDC in turn. I used an OTC 5609 cylinder leak tester. The compressor was set to 90 psi, but I never actually dialed the gauge up to full pressure because all four cylinders leaked 50% or more. All 4 cylinders showed hissing in the crankcase. Cylinder 2 also showed hissing in the exhaust. No hissing heard in the carb or bubbles in the radiator. Assuming I did the test right, my guess is that all 4 cylinders are just worn after 90 years of use. I don't think the engine has ever been rebuilt, certainly not to the extent of installing oversized pistons. So presumably the rings are not sealing well? Is there any repair for this other than a rebuild? The exhaust on cylinder 2 – I assume this is a burnt exhaust valve? Is that something I could repair without replacing the valve? Could I pull the head and clean up the valve seat or something? The car does still run, so despite the clear problems with the pistons I may elect not to fix them if I can fix the symptom of poor running at low RPM. Thanks for any suggestions.