Compression test readings: Re-carb backfire..

[Ed Griffin]

So far this was what I came up with on my motor. All plugs removed.

#1 cyl - 45 psi

#2 cyl - 30 psi

#3 cyl - 40 psi

#4 cyl - 35 psi

#5 cyl - 26 psi

#6 cyl - 55 psi

This was done with engine not running and no oil added to top of pistons to check for piston ring leak. To be honest I dont know how you can put oil on the piston from the spark plug hole. Chiltons says not to get oil on the valves when doing this test but with the holes above the valves other than number 6 cylinder being "reachable", how is this done?

I havent located what the standard high compression readings should be so far but from what I can remember shouldnt they be somewhere around 90 to 100 psi?

With these readings any suggestions what I should look at or try next?

Thanks in advance, Ed

Update:

I just located on past information that on a new engine 100 to 110 should be how much psi it would show. This engine is high mileage I beleave but am not positive. What's a decent reading for a tired engine?

Guess I should also mention that I did not open the throttle valve when I did this test as it states to do in the manual so i may have to go back and do it again.

[Merle Coggins]

I would suggest doing it again at WOT (Wide Open Throttle) for more accurate readings. If the throttle is closed it can't draw in enough air to compress.

Otherwise it doesn't look too bad. The readings aren't too far apart. The 30 psi difference between #5 and #6 may be alarming, but that may change if done again at WOT. If you had indeed bent a valve I would think it would be much lower, especially when done with a closed throttle.

As for getting oil into the cylinders... I've often wondered that same thing. The only thing I could think of would be to use a small tube to fish into the cylinder chamber and inject oil through that.

Merle

[rearview]

Closed throttle readings are worthless. Test must be done WFO.

I did mine in November and all were 110-115, no evidence of rebuild.

[Don Coatney]

Ed;

Good news is you do not have any bent valves. If you did there would be zero compression in that cylinder. Bad news is your compression is very low. You might have stuck rings. When you last had it running how much "blow-by" (smoke coming out of the oil fill tube) did you have? I think you should correct the timing issues and insure you are delivering spark to each cylinder at the right time. Then start it up and let it run up to tempertature.

On the oil in cylinder issue the oil will disperse under compression and find its way to the top of the piston.

On the open throttle issue it is bunk and not required to do so. There is always an open to atmospheric port to the intake manifold on these engines when doing a compression test. Think about it. As long as any intake valve is open there is a sourse of air at to the cylinder you are checking.

[Ed Griffin]

Don, If I were getting any blow-by I didnt notice any. There wasnt any fresh oil coming out of the filler tube and there's no wet mess around it like there would be if blow-by was bad. I did notice a little blue smoke from the exhaust but it wasnt heavy/thick coming out. Hardly noticed it when I did see it.

"On the oil in cylinder issue the oil will disperse under compression and find its way to the top of the piston."

So your saying that the engine oil is all thats needed and no need to put oil on top of the piston from spark plug holes?

"On the open throttle issue it is bunk and not required to do so."

I'm only going by what both manuals are saying on this.

I did the compression check again with the open throttle and got some odd readings compared to doing the test with it closed. Gained and lost compression on all but one cylinder. These are the last results of the compression test w/ wide open throttle:

#1 - 50 psi , gain of 5 psi from closed throttle

#2 - 34 psi , " ' 4 psi " " "

#3 - 36 psi , loss of 4 psi " " " (this is cyl with heli-coil, possibly air leaking)

#4 - 30 psi , loss of 5 psi " " "

#5 - 26 psi, no change " " "

#6 - 50 psi , loss of 5 psi " " "

[greg g]

Ed either your valves are sticking open, being held open by carbon, or may be burned (some sealing surfaces erroded) or you have a suspect head gasket. This would be evident as in 5 and 6. The cylinder pairs are siamesed, meaning there is a small space between paired cylinders. the head gasket commonly fails between siamesed pairs leading to a bleeding off of compression into the neighboring cylinder, and if that cylinder is on the an intake stroke, the compression from the neighbor will blow back through the open intake valve and throught the carb. I would suggest removing the head, inspecting the condition of the valvesand the head gasket. Since these areas are not open to colling passages, the typical symptom of bad head gaskets, spewing volumes of sweet smelling white smoke, will not be present. The area in the picture with the arrow pointing to it is where the failure commonly occurs in the gasket. You can see from the pic how the pairs of cylinders are positioned with the narrow casting and the wider casting with the coolant passages.

[david lazarus]

Having followed all this (and learnt a bit along the way) to remove the head is not a real major, will give you a good look inside AND an opportunity to really check your timing (all guesswork removed when you can see piston moving and valves shut!!!!).

If all is well with valve seats/bores it will only have cost you a new head gasket and a bit of time. It will also give you an opportunity to plane the head and repair the spark plug holes without more grud getting inside.

[Ed Griffin]

Greg, I've seen what your talking abt. on the previous refurbishing i did on the flathead I did on the first series 49 dodge I worked on abt the same time Don was building his big block. It is a very thin area between those cylinders and is where I noticed past leakage when i pulled the head before.

With this motor being an older Jasper factory exchange I imagine it has some miles on it. I'm going to give it another go at getting the timing set as Don mentioned but can see that not long from now the head will be coming off. If anything to put a differant head on so that the spark plug hole threads are better. Depending on the condition of the cylinders once the head has been removed it may just end up being pulled but I'd like to avoid that. Thanks for the feedback, Ed

[Normspeed]

On a motor that's been sitting quite a while the compression readings might be low because everything has dripped down, cylinders and rings are relatively dry. Shooting some oil in there will help. Also, pulling all the plugs before running the test helps, and let it crank til the comp guage stops going up, maybe 3-4 revs or more.

[randroid]

Ed,

May I respectfully request you do one more comp check before and after oiling and then compare the readings. There will be an increase in pressure after oiling and if it's slight then the head gasket and\or valves should be the culprit, but if you see the compression increase dramatically then your rings are in need of attention. I've used this method on a number of diagnosis over the years and it can be very revealing. Someone suggested pulling all the plugs before you spin the engine and this is a very good idea because it reduces the draw on your battery and wear on the starter. Spin the engine the same number of turns when you test each cylinder (8, 10, whatever) because compression will continue to build a slight amount with each turn and keeping everything equal will give you a more solid rock upon which you may build your decision as to what to do next.

You may also need to look at your bearings for wear as this can be a good indicator of how your lube system is working. Just drop the pan and pull the bearing caps then use "Plasti-Gage" to measure clearances, but do the double comp check first because bearings are a real can of worms if you're not experienced with them. (If you want a detailed account of how to do this PM me, but don't worry about it yet because bearings don't affect comp but will give you a basis for a more thorough diagnosis.)

If it is a head gasket, check the head for warpage with a straight edge put all over the head at all sorts of angles with a light behind it. That light will allow you see warpage measured in thousandths on an inch and the neat part is that your engine will no longer intimidate you but become your partner in keeping your drive on the road. It can be a lot of fun, no kidding!

-Randy

[Normspeed]

That's a great description on the comp check procedure. Randroid. Sounds like you've been there a few times

[Ed Griffin]

Randy, I'll follow up on your post tomarrow. Belly is full and "shops closed" for the evening

I do have one question for you that has yet to be answered. How do you put the oil in from the plug hole and how much are we talking abt.?

Will be back tomarrow, Ed

[Normspeed]

I just shot a couple squirts of motor oil with a trigger squirt can into each cylinder. She sure smoked a lot after I fired her up after that test. The neighbors were alarmed...

[JIPJOBXX]

My old 42 engine had so many miles on it that I had to have one cylinder resleeved. The cylinder wall was tapered toward the bottom and I could did not have enough material on the wall to grind it down straight. I could have gotten another engine for about 500 dollars but I wanted the numbers to match the car and so I just went ahead and had the engine completely rebuilt. Cost at the time around$1800 but well worth the money spent. Jon

[randroid]

Ed,

What Norm said. You'll be adding oil into your combustion chamber and it will smoke when you first start it and may even foul the plugs a little, but as easy as our plugs are to get at it's a small price to pay. You've already done a dry test so use something like a wood dowel to find a piston near the bottom of its stroke and shoot some oil into it with a squirt can, rolling the tip toward the outside of the cylinder. Use a lot on the first cylinder and after you take the first reading unscrew the tester and spin the engine, observing closely just how much oil gets sprayed out of the plug hole and over you and everything around you. Use less oil on the next one.

This procedure doesn't need to be done in the firing order of the engine; pick a cylinder near the bottom and check it next. I find it easier to use a piece of masking tape to mark which ones I've checked so I don't need to keep referring to notes and chasing pistons.

It's a half-hour job at worst and it will allow you to see inside your engine, a sort of relationship you will eventually find rewarding in a way that is better experienced than spoken. Maybe I'm sounding strange here, but I doubt many in this Forum would disagree with me.

-Randy

[Lou Earle]

Question- I do not have a manual handy- Do comp test engine cold? I have done mine in past running temp-is that wrong? Before I ran another test there are 2 things I would do.

1-Have only about 3 gallons of gas in the tank and add a can of sea foam and run the car about 30 miles over 40 mph.

2- a Coke bottle is best for this - get engine warm remove air filter and slowly pour the water into the carb revving her up to keep it running.

In my experience these 2 procedures will greatly clean up and remove tar ,varnish and carbon from the top end area.

Then run car and get it warm and check the compression. If your having stuck valves and they are not bent this will clean them up. Been there and done this on several engines ; besides I stayed at a motel 6 last night!!

I do NOt completely understand how this works but it does.

[Ed Griffin]

"It's a half-hour job at worst and it will allow you to see inside your engine, a sort of relationship you will eventually find rewarding in a way that is better experienced than spoken. Maybe I'm sounding strange here, but I doubt many in this Forum would disagree with me."

Randy, this isnt my first rodeo, I just have to be reminded how to get back in the saddle sometimes. I "refurbished" this one in 2003 and saw all you can see, touch, hone, replace.... so what you say doesnt sound strange to me. Well, maybe the squirt the oil all over me part but.. I'll try the wet test today, thanks.

Lou, from what I read, one manual says to do while engine is warm, another doesnt specify. In my case I have no choice since it wont start at all. Very glad you posted about the water and sea foam again. When I get this running I'd like to try both methods. I've heard the one on pouring into the carb only it was with transmission fluid. After reading your old post I've wanted to try that. I'm even tempted to try it on the 1957 283 motor in my truck but dont know if this method can be used on motors other than a flathead for whatever reasons.

Thank you everyone for your advice, I really do appreciate it, Ed

[Lou Earle]

I just poured a 1/2 can of sea foam thru my son's 302 mustang hi pro engine- the engine is a poor one but that cleared up the valve clatter- apparently sticking valves. I had already poured 12 Oz's of water in it to clear out the carbon etc.

Tim Adams when working at an unnamed Lincoln dealer in Ga used to pour 12 Oz's of water thru the big Lincoln engines as part of their 100 point or 101 point tune up!!!. They did this out back not in the shop!!!.

I think about the worst thing we can do to these buggies is run them under 45 for 4 or 5 miles and shut them down. I try and run each one of mine about 10 to 20 miles each month minimum to keep the deposits down

Lou

[dmulhall]

Did you have any end results?

I'm having the exact same problems

Thanks

[Ed Griffin]

I wish I did but the car still sits with the same problem. I took a 5 year break from the car after trying to diagnose the problem and it now sits under a metal cover. Now since it sits there I'll have to go at it like a car that's been sitting as well as the previous trouble but I'm still in no hurry because I've made my old truck priority for now. Sorry I could'nt provide any new info, Ed.

[Rusty O'Toole]

Ed what did you do to refurbish the motor and how long did it sit? My first impression is it is just plain worn out and ready for an overhaul. I have seen them with compression that low and would still start, with a little difficulty, and run without protest and without even making much noise. But very down on power.

The reason I ask is this. If the engine was rebuilt within the last 30 or 40,000 miles it should not be that worn. In that case stuck rings might be the culprit. Soaking the rings with Marvel Mystery Oil or similar substance, adding some to the crankcase as well, and driving for a few hundred miles might fix it. Otherwise plan on tearing the engine down for a rebuild.

[Ed Griffin]

I hadnt read the old thread again but from what I can tell is I mentioned the previous motor that I had refurbished as well as the motor that is in the the last D-24 that died on me. The last one that died on me and has the compression readings in the thread is the one thats still sitting in the car. That motor will most likely need a rebuild but will need more tinkering before going the rebuild route. The motor labeled as the refurbished engine sits in my other D-24 under cover. I have since learned that I will have to pull it again and check the main crank bearings. I did not use plastic gauge and when I had that motor running it had a bad knock when revved but ran strong when I got it going. At the time Don kept asking me if I used plastic gauge while working on it. At the time I had no clue to what it was but have since learned what it is and what it's for. I didnt want to admit I knew nothing abt it but have learned now that if I dont know to ask. Once I'm ready to mess with both motors I may just see if I can replace those main bearings, check how it runs and if it's a go, pull the other motor and put this one in. The motor sitting dead in my last car had been rebuilt at some time by Jasper motors but it wasnt a recent rebuild. If all else fails I'll find someone who can rebuild it. In all truth be told, I'd like to haul it to Tim Adams or Don C and get one of them to do it because then I'd know it was rebuilt correctly.

[mach0415]

I just pulled my 218 down for the same reasons. I stopped checking piston ring end gap when I found them to be in excess of .067" The top of the top compression ring was razor sharp, also indicative of excessive wear. I am in the middle of a rebuild after 30s and 50s compression numbers. All the valves and seats looked good.

[Ed Griffin]

This is the first engine I pulled from my first Dodge

This is the motor I ended up refurbishing with parts from two different blocks. This was before I purchased the 3rd D-24 (green) which has the dead motor. This went back in the second Dodge which is black.

This shows the green Dodge and the first one rusting in the background.

[yourpc48]

If you think its from sitting like everyone else I have a suggestion If you are not driving the car and dont mind letting it sit a little put some tranny fluid in each cylinder and then put towel over the holes and then crank it over with no plugs in it. Pour some more tranny fluid in the holes and let it sit for a couple of weeks with the spark plugs finger tight to keep moisture out. After waiting your week or two take the plugs back out and cover the holes again. Crank the snot out of it building up oil pressure to normal. Now run your compression test. If your rings were stuck the detergents and lubricating qualities of the trans fluid should have freed up the rings a bit. You will probably notice a difference in the compression. I did this with mine because it sat for 25 years in the blackberry bushes and it has decent compression now and I drive the car almost every day.

This was a trick that many old timers have told me. Even if you end up rebuilding it, this will clean up rings and pistons a bit and make taking it apart easier.

By the way. After doing this your car will smoke to beat heck till all that trans fluid gets burnt out of the exhaust system.