Hey guys. Just subscribed. Great video on the compression testing. This is a must for older engines to determine what needs to be done. Love the truck. I’m a Mercury guy and would love to find a M100 in decent shape. Keep up the good work. Len from Michigan.
Great video, can you elaborate on " disconnecting the coil " . I am newbie and would like to do this test just want to make sure what I need to disconnect. Thank you !
I would never install pistons or rings without honing the cylinder .The rings would likely not seat.Tried that once (Not honing).The car made a great mosquito fogger. By the way is there baffle under the PCV valve.Some aftermarket valve covers didn't have any.The baffle is important to keep oil out PCV valve.
Hi Jeff and Cam! Question? Is cylinder compression numbers related to overall compression ratios? i.e; high cylinder numbers like 10:5 to 1 or low cylinder numbers 8:5-1 or 9:5-1 perhaps? Thank you for any feedback. Appreciate you! Blessings from Motown/Dearborn.
It makes a slight difference, intake valve closing event makes the biggest difference in cranking compression. I have an engine I swapped heads on, went from 8.4:1 to 9.2:1 compression with different CC combustion chambers. I gained about 15 PSI cranking compression with the same camshaft in the engine. Old heads had good sealing valves, so that wasn't the difference.
As you test the compression on each cylinder it is normal for the range to increase as you test. This is because the cylinders are filling with gas more and more. Difference between wet and dry comression test.
Great info. Thanks. Question for you, as to what product and how much you think I should use. I have a 1995 Subaru 1.8L 4-CYL boxer Impreza, 177,000 miles. I have 76 and 78 PSI dry compression in #2 and 4 of one head (driver side). This started a few days ago, we noticed while on a highway trip the power was weak and I can hear it missing as the RPMs drop from driving to idle. I don't have overheating, excessive oil consumption (drippy seals, I add a quart about every 900 miles), smoking, or fluids cross contamination. I'm waiting to have a leak down and another dry/wet compression test at a different shop. The first shop only did dry compression and wasn't too bright or helpful. If I end up having a head gasket leak between those two cylinders, what products would I possibly try to mend it? It must not be too bad of a leak, whatever it is, for the compression to build to 78psi dry. The other two good cylinders are 130ish psi. If it ends up being a valve leak, what products and strength could I try to get them clean? After cleaning, I will have valve clearances checked, as it's probably never been done. Thanks again.
I would try some Seafoam in the fuel first if you are wanting to throw product at it. I'd want to see the wet test too. with the dry test showing 76 and 78psi, the oil test is the only other way you are going to find out.
I’m going to speculate that it could be wash down from fuel causing it. If you fix the dribbling carb, then run it for a bit and recheck it. And yeah when you tear it down and go through it, you’ll probably stop when you’ve replaced the ring and pinion along with the carrier bearings. 🤦♂️ Been there.
I’m dealing with this too, except my #3 piston gave me 30psi…. Didn’t put oil in yet but I’m getting oil accumulating in the air intake from blowby. I’m suspecting rings. I didn’t know you could drop out one cylinder from the bottom! I’d love to understand how to go about this more, is it possible on a 351w?
Should do a cylinder leak also. Stuck rings from misfire. Soak the cylinder overnight, run the engine, do another Ct and lt. more, but my finger is tired.
I have 61 thunderbird with 390 engine I found parked in the original owners barn where it had been since 1974 And recently, after changing the fuel pump, rebuilding the carburetor, changing the gas tank plugs and oil adding some marvels mystery to it I started it but after it warmed up a little smoke started coming out of the oil fill and somewhere lower on the other side of the engine and you can hear it missing, So I was just wondering do you think a compression check would tell me if I have worn rings or a valve that stuck? Thanks for any advice.
Worn engine for all the indicators u mentioned burning oil , fuel economy , fuming outta pcv more than normal low engine vacuum Compression test wet and dry dry first 8-10 cranks per cylinder more than 10% variation = bad Diagnosis ,,,wet test one cyl at a time same amount of oil squirts . Oil seals rings not valve sealing Then go to cyl leak down Engines can have compression but have real bad leak down less than 5 % new motor // worn out upto 10%leak down
