VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 26 chev engine rough

I have rebuilt this engine. A few things before I get to question. I have new pistons ,rings and a 1928 4 cylinder head and valves. All look good and purchased from Gary Wallace. Carb is a rebuilt RXO and appears to be working OK and no longer leaking. The engine just does not idle smooth and sometimes just cuts off during idle. I pulled the plugs out to compare. Number one plug is black and the rest appear to be firing consistently. I tested for spark and that is there, but I can not confirm if correctly. My thoughts; Is 28 head not compatible with RXO carb? Do I have a spark plug wire that sometimes fires but maybe not all the time? Could I have a valve sticking? Where should I start. I mixed up plugs with no change.

Bobk

Take one of the clean plugs and put it in one position clean the black one and use it where you took the other plug from. If one one is still black on next run then try moving a wire from one position and swap with one of the others wires clean the plug and then run the engine again then recheck one plug.

An engine rebuild catches my eye. Need to know what the re-builder did on the valves. Were guides installed and not reamed out to give clearance for the valves. Make sure the stems are lubed. Squirt some WD-40 or like lube on the stems. Check the valve clearance. Like I say, we need to know more about the valves.

Also, are the plug wires solid center wire and not modern plug wires. If the plug wires are old, check where they go over the top of the head for wear or overly oil soaked.

As you eliminate each probable cause you can isolate and solve the problem.

If engine cuts out intermittently ignition problem is most likely. Rough idle can be a multitude of causes. Intake manifold leak, valve leaking or adjusted to tight, short reach spark plugs, obstruction in intake passage, incorrect carburetor rebuild, plus others.

Are you sure of the cam timing? Did the rebuilder align the marks on the timing gears or count teeth on each gear and align by the diagram in the repair manual? The MAJORITY of timing gears are mis-marked. It was even a problem in the 1920s so it is mentioned in the 1928 Chevrolet Repair Manual. There is a diagram in the Manual counting the teeth from the keyways on each gear to get them correctly aligned. It is a problem that has occurred many times in recently rebuilt engines if the rebuilder relied on the the marks on the gears.

What ever you do, do not use WD40. I was a mechanic for a major airline for 28 years and the stuff was banned. Use a good lube oil like marvel mystery oil, STP or GIBBS (www.gibbsbrand.com). Gibbs is hard to find and I found some at a tractor / hit & miss engine show. We used STP when I was in school to rebuild small aircraft engines. All bearing surfaces and cylinder walls were coated with STP as it is real sticky and stayed in place.

Mike

I am rather surprised to find someone who agrees with me re: WD40. It's good for what it was originally intended for but that's it. It is not allowed in my garage or my wood shop. I haven't used it in well over a decade.

Excuse me while I run out the door before the war begins.

I think many folks have a misconception of the primary purpose of WD-40.... it wasnt to be a lubricant.

WD stand for "water displacement" and "40" was the fortieth formula tested ... squirt alittle into a distributor cap with mosture and you will see it work its magic.

Rocket Industries that invented it was located a few miles from my house in San Diego when it was first introduced in the late 50s-early 60s.

But I would be lost without it in my shop considering all its many other uses

If you assemble a brand new re-built engine using STP,or anything similar,rings bearings etc. will never bed themselves in properly.You'd be better off just using a good grade of engine oil.

There are many assembly lubes sold specifically to be the initial lubricant in new or rebuilt engines. There are also special cam lubes. I highly suggest you buy and use one of the major brands instead of the backyard alternates. Trying to save a few bucks can be very costly later on. I have been using them for 30+ years and never had an initial lubrication problem even when the rebuilt engine was not started for many, many months.

Your 28 head will be fine on your older engine. My first suspect would be plug wire if you already swapped plugs and problem didn't change. Second look would be to see if a valve is sticking. Press down on the valve with a chunk of wood and compress the spring and release, them pull up and listen for a click if it closes the rest of the way and make sure they are opening with the cam. My last experiance with getting a valve job done on an old 1929 International tractor engine with manually oiled valves was the shop wanted to get the valve stems too tight in the guides which causes sticking with the light valve spring rates these old engines have. May have to do with no oil pumped up on top of the head to carry off heat or just not much oil on the stem or possibly a tiny burr or dirt of somesort in the guide on assembly. Several tractor guys had this problem so I told my shop to not get the valve stem clearance too tight, I want them loose and I told them several times. I never had any problems. Plug wires should be solid core only. Run the engine at night and in the dark so you can see if any sparks are jumping off the wires. If you are using the wire conduit for a 28 valve cover, take the wire out and try looking at them in the dark while running. I have spotted many many bad wires just by watching the engine run in the dark. In fact I saw a tiny spark jumping from the wire to the sparkplug connector on my car the other night. I may have to pull the connector off and redo it.

I was the one who rebuilt the 26 chev 4. I know for a fact that I lined ny the marks. I am going to replace spark plug wires first but if this does not work I am going to pull timing cover. Do you have any documentation or link you can refer me to make the correction. This is a verified 26 chev 4 with rebuilt cam from Gary Wallace.

Bob K

The following is from page 30 of the May 1928 Service News.

The mark on the crankshaft gear should be "directly opposite keyway and fall between two teeth".

The mark on the camshaft gear is "located by starting to count with the tooth exactly opposite the keyway.... Calling this tooth No. 1, count anti-clockwise, or to the left, 15 teeth and punch mark the fifteenth tooth." "When mated properly, the tooth which is marked on camshaft gear should be matched with the mark on the crankshaft gear.."

FYI, There are many useful tips contained in the Service News, corrections and other valuable information. It is a good thing to have the year of your Chevrolet and a couple of years later so you have the additional reference in addition to your owners and repair manuals. I have a complete set from 1927 (start) to 1957. Use them often.

Re your RXO carby.
This is not your present problem, but will be a problem later on.
The valves in the 28 head are a lot bigger than the 25/26/27 early car valves. When the bigger valves were introduced in mid 27 Chev made a new carby, RAJXO for 27 and RAKXO for 28. These carbies supply more fuel to feed the bigger valves. Late 27's and 28's also had a bigger diameter inlet manifold.
Recently a mate who had an late 27 head, an RAJXO carby and the small manifold, replaced the manifold withe the bigger 28 and noticed the better performance immediately.
Chris

Thanks for your advice on camshaft alignment to crankshaft. I checked mine and it OK. My mark must have been done correctly.

Bobk

Have you checked the spark plug wires yet? Even new wires can be bad. If you have solid copper core wires check with an ohm meter to check the wire itself no good way to check the insulation without running the back of your hand along it while the engine is running, (Might think twice about doing that if you have heart problems, find a "sucker" or test dummy hehehehe!) Also sometimes you can hear the "pop" of the spark jumping out of the insulation and grounding. At very slow idle you can hear the engine miss or jump when the pop occures. Also have you done a compression check yet. That usually spots any compression imbalance (rough idle) right away. Also a vacuum gauge can spot problems.