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Automotive Technical Article

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GM Inline 6 cylinder engine

1-5-3-6-2-4 Cylinder Firing Order for GM Inline 6 cylinder engine.

1-5-3-6-2-4 Cylinder Firing Order

How-To Article: GM 235 C.I.D. In-Line 6 Cylinder Engine Overhaul

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Part One of Six


An overhaul procedure, in six parts, that includes a comprehensive sub-systems tear-down diagnostic, pertaining to a 1960's era Chevrolet Stovebolt 235 c.i.d. (3.9 L) in-line six cylinder engine.

The reader will find various appearances and versions of this icon in this article representing information the reader should make note of.Early versions of the straight six engine were given the “Stovebolt” nickname due to the bolts used on this engine resembled the hardware used on wood stoves of the era.

In this instance, there's not anything special to note here, however, if there was some little known aspect in the content of the text; this is where that jewel of knowledge would be placed for the reader to take note of. So don't forget to mouse-over these icons; otherwise you might miss out on some information you may find useful in your build process. The notable information is placed in the ALT of the image whereas the TITLE contains the name and version number of the image.

Updation is defined as: Past Technology Examined, OVER, Current Technology Applied,

Revised and updated article text by John Harlowe

Certified by the Automotive Service Excellence Organization as Master Automotive Technician, ASE certification number 1785-9774

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The original six part article titled “Rebuilding a Chevy Straight Six” was first published 27 years ago in 1995 and authored by Jim Richardson. The Author made numerous contributions to Classic Auto Restorer Magazine and this article's first public printing appeared in Chevy Trucks magazine the same year.

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The text on this page provides technical information and step-by-step how-to procedures regarding engine removal and a diagnostic disassembly sequence pertaining to in-line six cylinder engines manufactured by General Motors Corporation in the era from the mid-1950's through late-1960.

The 235 C.I.D. engine configuration is used in this article to provide a specific example in order to illustrate the various procedures and technical diagnostics brought to light in this technical article; all techno-speak regarding the 235 c.i.d (3.8 L) also applies to all GM inline six cylinder engines from the 181 c.i.d. (3.0 L) to the 292 c.i.d. (4.8 L).

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    Technical Information in this six part learning series also applies to the following General Motors Corporation engine configurations listed below:
  • 181 c.i.d. (3.0 L)
  • 194 c.i.d. (3.2 L)
  • 207 c.i.d. (3.4 L)
  • 216 c.i.d. (3.5 L)
  • 235 c.i.d. (3.8 L)
  • 250 c.i.d. (4.1 L)
  • 261 c.i.d. (4.3 L)
  • 292 c.i.d. (4.8 L)

Directional arrow to next information text section.

Part One Section 1A:

Prep and Removal of the GM 235 C.I.D. In-line 6 Cylinder Engine

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Removing the long and heavy 235 c.i.d. Inline six cylinder engine. Make sure the area the engine is overhauled in remains in super clean condition.

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The following introduction is taken verbatim from Jim Richardson's 1995 article:

“Over the years, I have torn up, torn down and tuned up a number of Chevrolet Stovebolt six-cylinder engines. These drive-train power-plants propelled me everywhere I wanted to go throughout my youth; sometimes under conditions that went well beyond their design envelope. I was 30 years old before I even tried living without a six-cylinder. Other brands of cars have graced my life, but I always missed the Chevrolet straight [ inline ] six cylinder engine. So when the news of an available 235 cubic inch displacement [ C.I.D. ] Stovebolt reached my ears, I jumped at the chance to take it home and rebuild it. For me this was like finding my favorite boyhood dog alive and ready to play again. Nostalgia may be a factor here, but I also regard this as one of General Motors best engine designs. ”

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“At this point I am not even sure what vehicle this 235 C.I.D. six cylinder engine will eventually be installed, but a 1957 Handyman wagon in need of a mill [ engine ] would be my ideal vehicle for this 235 C.I.D. six cylinder engine. In its early days, the Chevrolet straight-six Stovebolt was always upstaged by the peppier, more glamorous Ford flathead V-8, even though the General Motors configuration of the straight six engine was a more dependable and less troublesome in terms of part failures.”

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“Later, when the Chevrolet six was honed by years of development into the 235 C.I.D. of the mid-fifties, it was overshadowed by the company's own small block V-8, which is among the best American engines ever produced. The Chevrolet mid-1950 Stovebolt six cylinder engine is not as powerful as the V-8, but it is smoother, quieter, and more economical. Best of all, it is dead simple to work on.”

The more one learns the better the project outcome.

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You need to get dirty to create a clean vehicle.

What is the first item on the To-Do list of tasks for this project? Yep, that's correct-ohmundo my fellow sick-cylinder aficionados, the entire undercarriage of the vehicle needs degreasing. To be perfectly clear, a vehicle's undercarriage, for the purpose of this article, is defined as including the engine compartment.

There are several methods that can be used to accomplish the degrease of the vehicle's undercarriage. The best process for vehicle undercarriage degrease is the use of a steam cleaner. It should be noted at this point that a pressure washer, regardless if said pressure washer utilizes hot or cold solution, is NOT a steam cleaner. If one does not own a steam cleaner, should one purchase or rent a steam cleaner in order to accomplish a successful degreasing operation? No, there is no need to purchase a steam cleaner when a fair number of car wash outfits offer vehicle steam cleaning service. What is key here is to locate a car wash that has a vehicle hoist in their steam clean bay.

Clean up your act, prospective customers realize a greasy dirty shop and or workspace does NOT represent labor capable of producing peformance.

In the greater Los Angeles metro area, there are about a dozen such car wash outfits having a hoist in their steam clean bay ( the COVID debacle, along with more stringent environmental ordinances enacted in California, caused a significant reduction in the number of operational steam clean bays within car wash facilities in this State. )

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Current environmental controls require all waste water from "car" and or "engine / chassis" wash be recycled and reused after contaminants, such as clumps of petroleum infused chunks of dirt, are removed from solution. The volume of vehicle washes compared to the volume of engine / chassis steam cleaning is disproportionately low and this makes performing such service a premium.

So, after placing the vehicle on the trailer and carting it to the steam clean location, expect to pay around $500.00 for a complete engine / chassis steam clean.

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A small peek into the LowRyder Life

If you are not able to find a car wash facility having a steam clean bay, try reaching out to a few used car dealers. These used car dealers might not advertise a steam clean service, but it would be a good bet a used car dealer will have a steam clean bay devoted to their inventory. Ever see a dirty, greasy, dust-laden engine when you pop the hood on a vehicle for sale at a used car lot? Neither have I.

I'd first try dropping by a classic car / truck lot, it's almost a sure bet that such an outfit has their own in-house steam clean bay. I'd go onto the lot and start popin' hoods an gettin' down on all four and shine my mini Mag-Lite on the under-carriages of random vehicles until a dealer representative comes out to ask me WTF I am doing. At this point, I'd explain to the dealer rep what I need done and pull, like, three 100 dollar bills outta my pocket to entice an affirmative answer. In such a dealership, usually there's one or two employees that do "side-work" that you can realize substantial savings by having the steam cleaning done after-hours and or weekends, you just need to bring the vehicle to the agreed location at the agreed time.

Been working hard, cleaning, scrubbing, scraping, sanding all that crud on your chassis? Yeah, well, give yourself a break, take 15 and have a cold one.

Take a break, have a cold one.

Big Rig repair shops are a good bet too. Most of these shops will have a steam clean bay. What a big rig repair shop might not have in their steam clean bay is a hoist. If that's the case, then contract for a tow truck with the crab type wheel capture to lift the vehicle and NOT a sling that raises the vehicle by the bumper. Have the tow truck meet you at the steam cleaner. The tow truck lifts one end of the vehicle so the steam cleaner can do that part of the undercarriage and when done, the tow truck raises the other end of the vehicle for the steam cleaner to clean. Steam clean of the undercarriage shouldn't take more than 30 minutes a side, so you'll need to contact for an hour of tow truck time.

If the property around your house has enough level yard space to put down a tarp so that it extends at least four feet out on all sides when the vehicle is centered on the tarp; you can do the steam clean on your own property. you will need to surround the tarp with absorbent to create a 360° berm with products available from a company like New Pig.

New Pig: funny name, great products to contain and absorb the liquid mess that are unavoidable in frame-off vehicle restorations.

Image shows one type of absorbent kit New Pig offers to create a 360° berm along the edges of the debris and liquid contaminants catch-all tarp the vehicle to be steam cleaned is centered on.

If you want this crew to repair or maintain your vehicle, then, you are not at all sane. However, should you need your vehicle's frame and drive-train cleaned, then these are the idiots you want to hire. Don't be taken aback by the bibs these guys sometimes wear; they're prone to spontaneous drooling episodes.

The Degreasing Crew awaits their UBER beer delivery prior to starting the job.

Ok, you've laid out the tarp, and after centering the vehicle on the tarp, you lay down a berm around it and now you're ready to raise the vehicle. You'll need a low profile 3 ton (or more) capacity floor jack (max height should be at least 23.5 inches or higher) and 4 three-ton jack stands. FIRST place wheel chocks behind the rear tires, then raise the front of the vehicle to the maximum height of the floor jack and place the jack stands under the front left and right lower control arms. Then move the floor jack to the rear of the vehicle place the round lifting pad under the differential (pumpkin), by maneuvering the low profile floor jack through the side of the vehicle (NOT the rear) and raise the floor jack to maximum height and place the jack stands under the axle tubes.

Should you find the maximum height of the does not raise the vehicle to a height you feel comfortable working under, then, place a wood block horizontally across the floor jack's lifting pad. A 4x4 post (cut to a 6 inch length) and placed horizontally across the jack's circular lifting pad will add another 3½ inches, or so, to the total lift height.

If you need more height, then, along with the 4x4x6 inch long post on the jack's pad, use hardwood 8/4 (approximately 2" thick) plank that's S2S (surfaced two sides) and cut to a length of 48 inches; placing your jack on the plank will give an additional 1¾ inches of height. So then, using both the post and plank, adds about six inches in additional lift height. For example, if a floor jack's max lift height is 20 inches, by using the post and plank, max lift height increases to 26 inches.

Proper jack stand placement is critical to safety. Always place wood blocks on jack pad in the horizontal and NOT the verticle.

Special Shop Equipment Required

It's prerequisite that one use a Engine Sling with the Engine Hoist when removing or installing any displacement size of straight six engine. The difficulty level for engine removal and installation increases substantially should the Intake and Exhaust manifolds remain bolted to the engine block. So make life easy on your-own-self and keep the manifolds off ( along with any other items like the fan and generator / alternator ) that may cause clearance issues.

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When the engine is removed, it is essential to use a Heavy Duty Engine Stand so that one can work on the block without fear of the engine falling forward into the floor. Additionally, one MUST purchase GRADE EIGHT bolts, nuts and washers to be used with the engine sling and the engine stand. These straight six engines are heavy, very heavy and can twist 'n snap normal strength bolts very quickly. So don't end up as a bad mechanic cartoon, spend the additional dollars and go with the grade 8,

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Foldable engine stand designed to hold an engine block up to 2000 lb. without tipping over.

PITTSBURGH AUTOMOTIVE Brand 2000 Lb. Capacity Foldable Engine Stand designed to hold an engine block up to 2000 lb. without tipping over. Available at Harbor Freight for $160.00 as of June 2022.

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If you flat out cannot afford to have your pride ride chassis and drive train steam cleaned, then you need to do the cleaning job by hand. A caveat here, be prepared to be the dirtiest you have ever been. There's no way around this filth and grime cleaning task, and it is strongly suggested that you roll to the local Home Depot and buy your-own-self:

  • Two sets (MINIMUM) disposable coveralls
  • A couple (or three) face / head socks
  • At least box or two of 7 MIL (or thicker) heavy duty disposable nitrile gloves
  • Safety glasses or goggles (minimum two pairs)
  • One box of 25 N95 disposable respirators (AVG $ = $2.50 each)

    Filtering face-piece N95 respirators offer more protection against airborne particles than surgical masks or cloth face covers, because they are intended to be tight-fitting and can filter both large and small particles, including aerosols.

    Image of N95 disposable respirator.

  • Two pairs of LEATHER (or equivalent) work gloves

Then bounce to Harbor Freight and buy a tarp that fits your garage floor as best as possible. The tarp will catch all the toxic sludge you will be scraping off your vehicle's private parts; saving you the labor of acid washing your garage floor. However, if you, in all your car guru machismo-wisdom decide a tarp for your garage floor is NOT necessary. Then, as you gather your assortment of putty knifes, gasket scrapers and wire brushes to begin the removal of caked-on crud that's accumulated on the vehicle frame, engine and transmission for years upon decades; trust and believe me on this point, you will be wishing you weren't such a cheap bastard and had purchased that tarp and protective clothing.

After you have successfully de-gunked years of accumulated grease 'n grime, that now lay in assorted chunks all over your tarp, fire-up the shop vac and clean all that shit up. But don't roll that tarp up just yet because there's one more cleaning task that needs to be done.

Purchase a spray bottle and a gallon refill of Purple Power along with an assortment of nylon scrub brushes and spray the Purple Power on all the sections you have de-gunked, i.e., spray that stuff on everything!

Purple Power - the LEADER in industrial cleaners and degreasers.

Give the P.P. a few minutes soak time, then grab your brushes and start scrubbing as if a skunk sprayed your four year old nephew and you got picked to clean him up. After that, grab your garden hose or power washer and give everything you just scrubbed a good solid rinse. Lastly, fire up the air compressor, invert a tire valve stem (with the valve core removed) into the coupler of the air hose and blow dry everything.

Congratulations! At this point the vehicle cleaning task is done. Go have yourself a beer or a joint or both. If you did this task in your garage, then (as you have already realized during the process) you have, by default, also cleaned your garage. This is a good thing as your garage was dirty anyway and a clean work area for this type of project is necessary. Have you ever seen a bitchin' vehicle roll out of a dirty garage? Neither have I.

In this technologically expanding 21st Century, a medium grade cellular phone ( having a retail price between $300 to $400 ➜ circa mid 2022 ) will have more than enough photo features to create a web based photographic journal of your build if you so choose. Back in the day, most builders used a Polaroid Instant camera to capture the disassembly process; including the bolts, nuts, gaskets and other fasteners that belong with each sub-assembly, e.g., the water pump or intake manifold, documenting what goes with what and the total number of items each sub-assembly are supposed to have. Those who say "you always have a few left over bolts and nuts" are basically vocalizing their idiocy and you should stay as far away as possible from that type of person.

I have a dedicated Android cell phone ( which I consider a camera for builds and repairs ) and by dedicated, I mean it's NOT used for phone calls, texts, games or whatever; it's used exclusively for photos. Along with the Android, I use Google Photos ( free ) for storage and lite photo editing. Additionally, I use GIMP ( also free and Open Source ) when I need a more sophisticated image editor.

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What do you do with all those bolts, nuts, screws, washers, clips, brackets and what-have-you from the sub-assemblies after you have removed and photographed them? Well, you bag 'em up, so they don't get lost or mixed up in a collection they don't belong to. I recommend you purchase Zip-Lock™ freezer and sandwhich bags to keep these fastehers in. Along with the Zip-Locks™ get a couple of rolls of Manila ( color code #e7c9a9 ) masking tape; one roll having a 3 to 4 inch width and the other roll having a ½ width. Along with the tape, grab a couple of BLACK permanent markers and one yellow and one black paint pen; or pickup a multi-color paint pen set having extra fine .07 tips ( see photo )

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Section 1B : Removal of the Straight Six Engine


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