I've been struggling to get my 235 running as smoothly as it should. All new ignition parts and the valves are adjusted to spec. I've been driving it for a while and it runs and pulls pretty good. She fires right up. But there has always been some exhaust popping under load and at higher RPM's. Also, she idles very smoothly when cold but when she's fully warmed up there is some miss fire type sounds...not constantly but every so often the engine sounds like it skips a beat. Another thing, every so often after running at high RPM/high speed for a while I notice a slight smell of antifreeze but I always assumed I overfilled the radiator because it does leak from the small overflow tube at the bottom sometimes.
I decided to do a compression test today and wanted to share the results with you and get some opinions what you think is wrong, because there definitely is something wrong. I did this test on a cold engine, choke and throttle wide open. I have not tried squirting any oil in the cylinders and trying it again to rule in our out bad rings.
Here are the results by cylinder. Note: all of the spark plugs looked great when I removed them.
I've read a lot of threads on this here about low compression between adjacent cylinders and I think I might have a bad head gasket between the #1 and #2 cylinders. The motor does not overheat and I see not evidence of coolant and oil mixing in the engine or radiator.
Not even close- - - -a blown head gasket between adjacent cylinders causes either no or very low compression readings for both cylinders. 105 to 120 is almost within limits (10% between cylinders). I'm going to guess you've either got a tight valve adjustment or a slightly leaky valve on #1. Always do a valve adjustment first before checking compression and then warm the engine up fully first. If you get similar compression readings on a hot engine with properly-adjusted valves, then do a cylinder leakdown test to figure out where the compression is going. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
It looks like I missed that little detail. Pulling a cylinder head can actually hide the source of a minor compression loss. Putting air pressure into a cylinder through the spark plug hole with both valves fully closed and the crankshaft locked by putting the trans in gear and setting the parking brake or chocking the wheels can pinpoint the leak. Listen at the carburetor, tail pipe, and oil filler cap to see what's leaking, and do the same thing for every cylinder. Bubbles in the radiator indicate a head gasket leak into the cooling system, or maybe a cracked head or cylinder wall.
If you set the air pressure to 100 PSI with no air flowing, the pressure the cylinder is able to maintain translates to a "percent of leakage" measurement. 90 PSI = 10% leakdown, etc. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Read all the posts, thank you for the feedback. Tomorrow i'll run the engine up to operating temperature and perform another compression test.
I adjusted the valves on the loose side so I don't think it's a tight valve. Intakes are set to .008 and exhaust are set to ,020. If it's not head gasket related then I was thinking maybe a burnt exhaust valve on the #1 cylinder. One way or another we have to figure it out. I'm really hoping it is not a cracked head or cylinder wall...please don't let it be that.
I'll be back tomorrow and let you know what my compression readings are on a warm engine. I don't have a leak down test kit at home but I think I might be able to borrow one from a friend. That test will have to wait until I get my hands on a kit.
All you really need is an air hose and an old spark plug. File, grind, or hacksaw the crimp on the plug shell to release the porcelain and use a 1/4" pipe tap to thread the plug shell for an air line quick-connector. I've got a couple of those adapters stashed away somewhere, one for 14MM plug threads and another for the old Ford 18MM plugs. One of these days, I'll have to make one for the 10MM threads on some of the old 216's.
If you have a compression tester with screw-in adapters for the plug holes, just take the Schrader valve out of the tester hose and adapt the air pressure to it. A lot of compression testers use the same quick-connect fittings that air hose couplers have. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Hello all, well I decided to cut to the chase and check for leaks. I made a shade tree leak down tester (thank you Jerry). I set my compressor to 30lbs and hit the cylinder. I found that on cylinder #1 at TCD, air was coming out of the exhaust. I didn't hear air anywhere else, or see any bubbles in radiator. I checked cylinder #2 since it was a little lower then the rest too and did not hear anything at the exhaust, carb, breather or dip stick tube...and I didnt see any bubbles in the coolant.
I guess I have a burnt exhaust valve in cylinder #1. Is there any other reason air would be escaping out of the exhaust?
Either way, I suppose i'll be pulling the head this weekend and visiting the machine shop on Monday. Good thing the tax return is coming soon.
Before you take it apart, try this- - - -with the air pressure on #1, give the top of the exhaust rocker arm a few sharp raps with a dead blow mallet or a non-marring hammer of some sort. If there's a carbon deposit on the valve face or the valve seat, it's possible to dislodge the deposits and make a noticeable change in the amount of leakage. If you can make a noticeable difference, go to "Plan B"
Run the engine until it reaches normal operating temperature, and set the idle speed screw to a fairly fast idle speed- - - - -1500 RPM or so. Fill a Coke bottle with VERY hot water- - - -almost boiling, and slowly dribble it down the carburetor throat. When the hot water hits the combustion chamber it will flash to steam almost instantly and "steam clean" the combustion chamber, valves, valve seats, etc. It won't fix a burned valve, obviously, but if the problem is a carboned-up valve or seat, I've seen some pretty dramatic improvement, without ever turning a bolt! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Got it Jerry, i'll try that tomorrow. I've got a dead blow hammer, and I've got air pressure! I'll probably pull the rocker shaft/arm assembly (pretty easy to do on these engines) and give her a go. I'll let you all know if there is any change.
There's no real need to pull the rockers- - - -there are two shafts that plug into a central piece called an "oil connector" and the whole assembly requires about four hands to reinstall. Just to do the shock check for carbon deposits, a few licks on top of the rocker arm tip right over the valve stem won't hurt anything. Just be careful not to get the pushrod out of alignment with the adjuster. If you don't see much change in the leak, you'll probably need to pull the head, but try the hot water trick anyway. No cost involved, and there's not really any way to do any damage. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
You don't want to know what my compression is. You would wonder how it runs. The truck runs pretty good. Doesn't smoke or anything like that but does have the same symptoms as yours. I've got to get busy and find the problem. One thing for certain, if you listen to hot rod he can get you through just about anything. He has so much knowledge on these old trucks. Wish I could get him out here and give him the go ahead on my truck. Good luck!
I've seen good-running engines with compression pressure as low as 60 PSI. The trick is to have as little variation between cylinders as possible so there's very little difference in power impulses. One cylinder that's very low on compression causes a lope as the engine runs.
Another diagnostic tool is called a "power balance test". Connect a vacuum gauge and a tachometer and run the engine at a constant fast idle. Disable the spark to a particular cylinder by pulling a plug wire and watch the drop in RPM and manifold vacuum. Disabling a cylinder that's not pulling its weight will result in little or no change in RPM and vacuum, and one with a burned intake valve might actually cause the engine to speed up due to less dilution of the intake mixture. An even more definitive version of the power balance test is done by running the engine on only the companion cylinders (1 and 6, 2 and 5, and 3 and 4, for instance) and monitoring RPM and vacuum. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Ok I'm back with an update. I tried your rocker tapping trick Jerry but no dice...she's still leaking out of the exhaust port on cylinder #1.
I've got everything apart and will be pulling the head tomorrow morning. I tried to pull it today but I just didn't have the strength to lift it out of the engine compartment by myself without possibly damaging something else on the way out.
It's going to the machine shop...i'll see what they recommend, it's a small shop and they know these inline 6's.
As far as gaskets go...i'm just going to buy a complete upper end kit from Fel-Pro.
Question is...should I go with the fancy copper faced head gasket or stick with the fiber based gasket?
The copper gaskets are mostly used on high performance engines. Unless you've got plans to hotrod it, the plain gasket should be adequate. Have fun! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Just for giggles, when you get the head off, tilt it up so the intake and exhaust ports are facing up. Then pour some solvent, anything will do, mineral spirits, turps, kero, into the ports, you should see leaks out of the valves that are in bad shape.
I myself prefer the copper gaskets but I think that is probably because that is what I have mostly used over the years on these motors. They are becoming a little scarce these days. I have used the newer non copper gaskets on these motors and have not had a failure so it appears you could use either, whatever you can get your hands on.
Once upon a time, there was a thin shim solid copper head gasket available- - - -.060" thick, IIRC. It was advertised as a "high compression head gasket" by places like J.C. Whitney. If the head and block sealing surfaces were perfectly flat, it worked OK, but I was always a little skeptical about the claims that compression could be increased by using a head gasket half as thick as the original sandwich-style gasket. On the alcohol-burning tractor pull hemi engines we used to machine a groove in the block for a stainless steel O ring and bolt 'em together with a thin copper head gasket, but those engines got torn down often, and the only place we ran coolant was in the cylinder heads. The water jacket in the block was filled with hard green epoxy to reinforce the cylinder walls. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Well I got the head off this morning and inspected the valves and the number one cylinder intake valve was burnt...it had nearly a quarter inch crack in it. I dropped the head off at the machine shop this morning. I'll update when I hear back from the shop.
Hi Drag...yes it look like the valve had burnt a bit as the metal was thinner on a small portion of the edge...got my glass on and took a closer look and sure enough a hair line crack had developed as well.
Now the task of cleaning the block (it's still in place on the frame)...I"m a little nervous about that and how best to keep crap from falling down those push rod galleries. I think i'll try and plug them with something and get the shop vac out and vacuum right where I am cleaning as I go.
Don't be nervous. Slow, careful, clean work is the rule of the day. Do yourself a favor though. You have the motor this far apart, go a little further. I think you are working with a 55 block. Pull the side cover. There are two oil drain back holes (in between the lifters). Plug these up with corks or something. Then carefully clean the top of the block. Then, pull the steel line that is behind the cover and clean it out really spick and span. Take a close look at the boss at the rear cam bearing (where the lower part of the line was installed). Make sure its not clogged or restricted. If it is, gently clean it out. When you get the head back from the machine shop, scrub it up nice and clean. Pull the hex plug from the side of the head and make sure the boss at the underside(where the upper part of the line was installed) is clear right up to the top of the head. This is the oil feed for the rockers, the hex head plug is a direct path so clean it all out. This is where the restriction is generally found that limits the oil feed to the rockers. Gum and built up gunk. Scrub the rockers clean. Having the rockers rebuilt is expensive so you want to do all that you can to keep them supplied with oil (not to mention the oiling feature for the rocker tips and push rod cups, and the cooling feature of the oil on the springs). Clean the cover, new gasket and you are all set. Remember to remove the plugs. I like to use a little speck of white assembly grease on my push rod cups and rocker tips when reassembling.
Burned exhaust valves are sometimes the result of one too many valve jobs, in my experience. There needs to be a "margin" at the edge of the valve that's about 1/16" or more. If the valve gets ground to a knife edge the heat of the exhaust gas going past it several times a second will cause the valve to curl up, leak, and burn. Fortunately, 235 exhaust valves are the same size and length as small block V8 exhausts, and stainless steel valves are plentiful and dirt cheap. If you are willing to do a little pocket porting and valve seat grinding, a 1.6" small block exhaust valve can be fitted to the stovebolt head. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Once upon a time, there was a thin shim solid copper head gasket available- - - -.060" thick, IIRC. It was advertised as a "high compression head gasket" by places like J.C. Whitney. If the head and block sealing surfaces were perfectly flat, it worked OK, but I was always a little skeptical about the claims that compression could be increased by using a head gasket half as thick as the original sandwich-style gasket. On the alcohol-burning tractor pull hemi engines we used to machine a groove in the block for a stainless steel O ring and bolt 'em together with a thin copper head gasket, but those engines got torn down often, and the only place we ran coolant was in the cylinder heads. The water jacket in the block was filled with hard green epoxy to reinforce the cylinder walls. Jerry
.060 seems thick not thin. Can you elaborate to the regular gasket thickness?
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Most sandwich-type head gaskets were in the neighborhood of .120" or so- - - -two thin pieces of steel sheet metal with a composition fiber layer between them. The heads had to be torqued, then the engine was run to operating temp, and the final torque sequence and readjustment of the valves was done after a cool down period. Supposedly, the sandwich-style gaskets would take a set and loosen the torque values on the initial run-in. In the 1960's Fel-Pro introduced a "no-retorque" sandwich gasket. There have always been single layer steel head gaskets of about .025" thickness that were intended to be installed with a thin layer of brush-on sealer which were used as OEM parts because they helped speed up the production line. I really doubt that engines coming off an assembly line got heat/retorque/adjust sequence. Any head gasket leaks probably got addressed in the dealer's service department under warranty. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Hi all, quick update, I should be hearing from the machine shop mid week. I starting cleaning the top of the block off...just taking my time, slowly but surely. While I'm waiting for the work to be completed, I did have a question about the rocker shaft oiler that that feeds rocker arms. Mine looks to be original, it loops around the rocker shaft and dumps overflow oil back onto the head. Before I took the head off, I did observe the engine running with the valve cover off and oil was getting to the rockers (I'd like to see more!) and there was a good flow coming out of the oiler and back to the engine. I guess that is a good sign that there isn't any clogged passageways that feed that system. I did inspect the rocker arms and they are all the correct ones for my year 235 with the oil groves machined in the middle of the rockers matching up with the oil passages in the rocker shafts. I inspected the rocker shafts and I did not see or feel any obstruction in the oil passages.
All of that being said, for my 1955 235 engine, is there any advantage or disadvantage to crimping that rocker oiler after it feeds into the rocker shaft (like the later 235's have) to get more oil to the rocker arms? Should I just leave well enough alone?
If oil is coming from the weep holes in the top of the rocker arms, you're getting enough lubrication "as is". Remember that at idle, the oil going to the rockers is going to be minimal due to low oil pump volume- - - -once you're out on the road, the flow will be much greater due to higher engine speed. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
You could pinch it off. Lots of them were over the years. But the reason they were pinched off was because of diminishing oil feeding the the rockers. Worn rear cam bearing, worn engine bearings overall. Clogged passages, clogged feed line and passage in the head. It was a band aid. If all of your rockers are dribbling oil, not spitting all over creation, dribbling, particularly the rockers for no. 1 and 6, and the rocker adjuster ball and push rod cup look to be getting lubricated, and the valve tips and rocker arm tip also looks to be getting lubricated, then you are good to go. Too much flow and pressure, the oil spits past the rocker arms so that the adjuster balls and push rod cups get no or little lubricant, taking out the adjuster balls which are a big pain to find replacements for these days, and the oil spits past the valve tip and rocker arm tip, and the springs get no coolant. So resist the temptation to creat more pressure and flow if you already have what is needed and required.
I heard from the machine shop on Tuesday, my head should be ready for pick up Tomorrow.
Good news was no cracks, shop said the head was in good shape. Shop inspected the rocker shafts and arms and found that they were still good to go. I'll let you guys know what work was done on the head to get her back in shape when I get it back.
Hello guys, been a while since an update. I got my head back from the machine shop today. Can't wait to start putting the engine back together. All said and done it was still in pretty good shape. The head didn't have any cracks. We replaced all of the exhaust valves, valve guides, gaskets, and put in hardened seats. The intake valves on all the cylinders were in good shape so we decided to keep them. The were cleaned up and reinstalled. We did replace all 12 valve springs. The head was resurfaced and it looks good.
The shop inspected my rockers and shafts and they were also in good shape so we left them alone.
Good show- - - -it sounds like you've got an above-average machine shop. Hardened valve seats are sort of overkill, unless you're planning to do a lot of heavy load-pulling at full throttle. Most restoration jobs don't see the kind of abuse that requires hard seats, even with unleaded gas, but as long as they're installed properly, Stellite seats are OK. About the only time I consider them to be a necessity is on LP gas powered engines. If you're running a new cam and lifters, be sure to do a good break-in run before you idle the engine much. During the first 20-30 minutes of operation on a new cam it's important to run the engine at a fast idle or above to assure plenty of oil gets splashed onto the cam and lifters by the connecting rods. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Had some help and got the head back on the block. Just a couple of pictures of where we are at now. Going to try and get her completely back together this weekend.
Thanks again for all of your help...more to come in a few days.
