Rebuilding an Engine


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How to Rebuild an Engine

Yes, that's a picture of an old clunky mower, but there's much more information below on engine rebuilding.  It just so happens that my engine experience began with an old lawnmower engine.  I can still remember that first engine rebuild.  I was the type of kid that was curious about how things worked.  At that age, more often than not, I'd take things apart and then not be able to get them back together.  If I did get things put back together, I'd usually have an assortment of "unnecessary" parts and bolts left over!  At least I figured they must be unnecessary, because I didn't know where they belonged!  Anyway, my first exposure to an engine rebuild was with an old lawnmower.  We had a neighbor which had an old mower sitting out in a field on their property.  The weeds were growing around it.  The mower had obviously not been used for a long time.  I asked the neighbor about it and they said that it was dead.  I asked if they wanted it.  They didn't want it and they said I could have it, so I dragged it home.  I wanted to take it apart to see Mower Engine Rebuildhow the engine worked.  At that time, I was really too young to rebuild an engine on my own, but thankfully my Dad had some experience with that and so he helped me out.  Actually, he did almost all the work.  When we removed the cylinder head on this old broken down mower, we discovered that the cylinder was badly scored and worn.  We discovered that the engine bore itself was actually just made out of cast aluminum!  The cast aluminum crankcase did not have a steel cylinder liner.  At the engine factory (this was an old Briggs), they just machined the cast aluminum crankcase and cylinder bore and called it good.  Well, about the only thing an engine like this is good for is cheaper manufacturing costs.  These throwaway engines have hard steel piston rings rubbing in a soft aluminum bore.  How can that last!  Sometimes you see the phrase "Cool Bore" referring to small engines that have a "cool" aluminum bore.  Sure, maybe the aluminum cylinder bore will conduct the heat away a little quicker than a cast iron cylinder sleeve.  So what!  The aluminum cylinder bore will be worn out so fast, that this cool bore marketing bunk is just a distraction from the fact that these are cheap, junk engines.  Anyway, even though we knew this engine was not built to last, we decided to try and salvage it and get the mower running again.  My Dad made a simple honing tool that had some strips of sandpaper on small wooden blocks.  We used this to hone the cylinder with a hand drill.  We were basically trying to put a crosshatched honed surface in the cylinder bore.  This crosshatching is what helps retain oil which keeps a film of oil between the piston rings and the cylinder surface.  We put in a new set of rings and after getting the engine all back together, it actually ran very well and was used to periodically mow a large weedy area on my parent's property for many years.  In fact, last I noticed, my Dad still had that old mower sitting around 30+ years later; however, it was no longer being used because the steel mower deck was rusted through so badly.  What's a rusty old lawnmower have to do with rebuilding an engine?  A lot!  You've got to start some where.  Personally, I went on from that clunky old mower to work on motorcycles, cars, and various other engines.

CL70 and CB360 Motorcycles

Back in the 80's - My First Motorcycles - 1969 Honda CL70 & 1975 Honda CB360

This leads me into some engine rebuild experiences that I had with motorcycles.  My very first motorcycle was a 1969 Honda CL70.  I was a kid and we were driving home from church one day.  On our way home, I noticed a garage sale going on with a motorcycle sitting out with a for sale sign.  I begged my Dad to stop and so he did.  That's when I first saw my faithful old CL70.  I wanted a motorcycle so bad, and I pleaded with my parents to let me buy it.  They agreed.  $75 dollars later we were headed home with my first motorcycle.  I drove that thing for many years as a kid.  It was really meant for riding on the road, but I put a knobby tire on back and drove 1000's of miles on trails near my parent's house.  I'm not saying that the trails were 1000's of miles long.  I'm saying that I drove on the same trails, natural gas line access roads, & powerline access roads over and over and over!  Riding my motorcycle was a way to burn off steam and get away from the stress of schoolwork.  I didn't get anywhere too fast (top speed was around 45 mph downhill), but I could go most places even if it was at a slower pace.  I never really needed to tear into the CL70 engine too deep.  It was a very reliable engine.  I have many memories of riding the CL70 over the years.  One particularly memorable moment was when I was home from college during a break.  I had a buddy with me, and we decided to go out trail riding.  At that time, I had an XL250 that I primarily rode off road.  I let my buddy ride the nicer XL250, and I loafed along on the old CL70.  Even though I was slower, but since I was familiar with the trails, I led the way.  We came to a familiar place where there was a hill that ended in a low spot that had standing water during the rainy season.  I had gone through that water many times.  I knew where to go and I wasn't worried about hidden rocks or logs, because I had crossed there so many times.  There was one difference this time.  The large "puddle" looked more like a small pond this time.  It must have been extra rainy during that season.  In any case, I was a little hesitant to try to cross so much water, but with my buddy waiting behind me, I decided to show off a little and cross through the water at high speeds to make a big splash.  Well, I made a big splash alright!  Half way through the water crossing, the engine died.  I was up to my chest in water!  My motorcycle was completely submerged underwater!  I submarined my motorcycle!  To make a long story shorter, I dragged my dead motorcycle out of the water and pushed it to a paved road.  I then went and got the family station wagon and transported my dead motorcycle home.  I thought that I had ruined the engine.  Ingesting water into an engine at high RPM can be disastrous.  Unlike air, water does not compress, and so water can hydraulic lock the engine leading to serious damage.  Amazingly, I just ended up draining the water out of the gas tank, carburetor, and crankcase.  After cleaning out the carburetor some, the little 70cc engine ran as good as ever!  Over the years, I worked on that CL70 engine some, but not nearly as much as my Honda CB360.

My next motorcycle was a '75 Honda CB360.  I first saw this motorcycle sitting by the side of the road near the fire station with a for sale sign on it.  It was beat up and had some obvious problems, but the price was right.  Again, I begged my parents to let me buy it.  At that time, I still did not yet have my license.  My Dad rode it home even though it had a broken clutch cable.  I knew that I had some work to do on it, and I decided to go through and do a complete engine rebuild.  At that point in my life, I had more experience working with tools and knew more about how to rebuild an engine, and so I tackled this project on my own.  If memory serves me right, I also bought a service manual for CB360 and this helped a lot.  I tore it down all the way to the point of splitting the crankcases as you can see below in the scanned image of an old picture.  This was a big deal for me, because I had never torn that deep into an engine on my own before.   

CB360 Engine Rebuild

Splitting the Crankcase During an Engine Rebuild on my CB360

I bought new pistons and rings, a full gasket set, and I set out to rebuild this twin cylinder engine.  I took the cylinder block, along with the new pistons and rings, to a machine shop experienced with engine rebuilds.  They bored the cylinders out to match the oversized pistons.  When I got the cylinder block back, I slowly began to put things back together.  From the time that I got this motorcycle, to the time that I was done rebuilding the engine, many months had passed.  I invested a lot of time and money (for a kid) into this project.  Then finally one day, I was all done.  Everything was back together.  With eager anticipation, I decided to take my maiden voyage on the dead end street where we lived.  It was a couple miles long and it would be a good place to start to break in my newly rebuilt engine.  Fuel petcock open with choke on, I cranked over my freshly rebuilt CB360, and it roared to life.  I had taken the exhaust pipes to high school metal shop and cut open the mufflers and gutted them out.  I then welded them back together.  They were now just straight pipes, and they really roared!  As I went down our gravel driveway and out onto the paved road, I was filled with excitement.  I also felt a great sense of satisfaction, knowing that I had rebuilt this engine and everything was working great.  Well, that excitement and satisfaction quickly changed to great disappointment!  A couple miles into my maiden voyage, all of a sudden a clattering noise started coming from the engine.  It was very loud.  Something was seriously wrong.  I thought the worst; I figured the engine was ruined.  I limped home with this mortally wounded motorcycle, and my sense of pride and satisfaction were mortally wounded as well.  In fact, I was so disappointed that I just parked the bike and let it sit for a long time.  A few months later, I finally had the motivation to do an autopsy to open up the engine to see what had happened.  My imagination had all sorts of negative ideas about how the engine was ruined.  As it turns out, it wasn't as bad as I had thought.  What had happened was the cam chain tensioner had jumped out of it's lower retaining cup and fallen down into the crankcase where it was grinding and clattering around against the moving parts.  I concluded that the cam chain was stretched so far that the cam chain tensioner had to flex and extend out so far to take up the slack, that it ended up jumping out of it's lower retainer.  While I was rebuilding the engine, one of the things that I didn't buy (but should have since this was a high mileage engine) was a new cam chain.  I thought about buying one, but I figured that the cam chain is always flooded with clean engine oil inside the crankcase, so it shouldn't be too badly worn.  It looked fine to me, but obviously I didn't examine it closely enough.  With a second chance still available, I installed a new cam chain and got the engine back together again.  Fortunately, the engine ran great after that.  Even though the 360 engine was very mild by today's standards (and even for back then), it sure sounded fast!  At full throttle with the exhaust roaring at 9,000 RPM through those open pipes, it sounded like a drag racer!  I had a lot of fun on that motorcycle, and in the end I learned many lessons about rebuilding engines.

Even though I tried to be very careful rebuilding that engine, and even though I had prior experience working on engines, I still learned some new lessons through the School of Hard Knocks!  All that to say, if you've never rebuilt an engine, then you need to be realistic in your expectations.  It's not something that most people are going to be able to do properly without some prior experience.  At the very least, you will need help from someone that has some engine rebuilding experience.  An exception to this might be someone that has had a lot of experience working with tools on other mechanical equipment.  Maybe they don't specifically know how to rebuild an engine, but they are proficient with their hands and with tools, and so they are more likely to be able to transfer these skills to working on engines.  Below, I will highlight some of the things that I've learned over the years while working on engines.

1)  YOU NEED THE RIGHT PARTS - Just like I learned on my CB360 engine, you need to be sure to replace all the worn parts during an engine rebuild.  That means that as you take apart the engine, you need to carefully examine each component to determine if it is suitable to reuse or if it should be replaced.  At the very least, you will need a full gasket set while rebuilding an engine.  Pistons and rings will most likely need to be replaced.  Bearings, camshaft, gaskets, and seals are also typically replaced.  If you can afford it, try to buy original factory parts for your engine.  Don't skimp on the parts, because the labor involved and the time invested are too great to be wasted on cheap parts that may cause you problems later.  Try to use OEM parts or at least aftermarket parts that come from a company with a solid reputation for quality.  

Engine Rebuild Kit

2)  YOU NEED THE RIGHT TOOLS - This is true in many areas of life, but the reality is that some people don't really understand that you are not going to be able to rebuild an engine with a few household tools.  If you were going in for surgery, you wouldn't expect the surgeon to pull out a set of kitchen utensils and start carving you up with a kitchen knife!  In the same way, while rebuilding an engine, you will need to have the right tools that are properly matched to the job at hand.  At the very minimum, you will need to have some basic hand tools like the following:

  • Complete socket set
  • Combination open/closed end wrenches
  • Torque wrench for tightening critical fasteners to spec
  • Set of allen wrenches (not used as often, but still good to have)
  • Set of different sized screwdrivers including blade (straight) and Phillips head
  • Measurement tools such as calipers, micrometers, and various gauges for measuring engine specs

Keep in mind that you will need SAE sized tools if you are working on an older American made engine.  Foreign made engines will require Metric sized tools.  Some situations may require both SAE and Metric.  As a result, it's a good idea to have both SAE and Metric hand tools.  When shopping for hand tools, I'd recommend that you invest in good quality tools.  If you plan to use them a lot, then consider buying quality tools such as Craftsman or Snap On.  I have an old Craftsman socket set that I got as a gift when I was a boy, and I still have that socket set today and still use if frequently.  I've used that socket set on many different projects and a lot of different engines over the years.  Good quality tools will last.  Furthermore, you don't want to have a tool break at the most inopportune moment.  Not only will you be slowed down in your engine rebuild progress, but you will also have a greater risk for injury.  Even with good tools, you can still hurt yourself.  I can still see scars on my hands from times when the tool slipped and my hand was gashed by a sharp edge somewhere.  This can happen even with good tools if you are not careful, but a cheap tool breaking unexpectedly can greatly increase the chances of hurting yourself. 

 In addition to the basic tools listed above, you may also need some tools to remove special fasteners like Torx bolts in some cases.  Then there are other specialty tools that might be needed like special pullers to remove pulleys.  There are other special tools that might be needed for various things.  Even something as simple as disconnecting a fuel line these days on a modern vehicle can require a special tool.  Generally, I've found that it's best to just buy the specialty tools on an as needed basis.  In addition, you can sometimes "rent" specialty tools from your local auto parts store.  Some of the auto parts store chains provide tools to their customers as a courtesy.  They don't just do this to be nice.  They are doing it so that they can gain too.  Basically, they are trying to encourage you to do the repair yourself and buy the parts from them.  The way that it usually works is that you buy the tool upfront.  Then when you are done using it and bring it back, the store gives you a full refund.  By doing it this way, they don't have to worry about their rental tools disappearing.  If the tool is not returned, then the person already paid for it, so it's no loss to the store.  In any case, this can be a good way to use some expensive, specialty tools for free.

Engine Block Honing

Engine Block Being Prepped for Honing at an Experienced Machine Shop

A final note about tools.  Even if you have all the tools listed above, then you are still not going to have everything you need to rebuild an engine.  A complete rebuild requires special machines that will only be found in machine shops set up for rebuilding engines.  In order to be able to bore and/or hone a cylinder, you need to have a special machine.  In order to be able to grind valves and valve seats, you need to have special equipment.  If the cylinder head is not flat and needs to be machined, or if the engine block needs to be decked to true up the top surface, both of these machining operations require special equipment.  The list can go on.  The point is that you can only do so much by yourself in an engine rebuild.  Unless you have your own machine shop, at some point you will need to take parts of your engine to a shop that has the right tools and equipment to help do the work necessary to rebuild your engine.  In reality, an engine rebuild for most people will look something like this:  remove the engine from the vehicle or machine, take apart the engine, verify what needs to be done on your particular engine, buy whatever new components and gaskets are needed, take the necessary engine parts to a shop for machining, put the engine back together, and finally reinstall the engine.

3)  YOU NEED THE RIGHT PLACE - This is also very important.  You can not just expect to rebuild an engine working in the dirt.  Cleanliness is CRITICAL in any engine rebuild.  You need to have a place where you can carefully take apart the engine and keep things clean.  In addition, you want to do all this in a protected environment where rain can not get into your engine while you have things disassembled.  You do not want rust on any internal engine parts.  This is especially true on cylinder walls, but you don't want rust anywhere inside the engine.  I have worked on engines in environments that were very hot and humid, and I had to even be careful about the sweat dripping off my head.  Salty sweat dripping on a critical surface like a cylinder wall or a camshaft lobe is not good.  Sure, a little surface rust won't destroy the engine, but it's not going to help anything either.  Better to protect your engine from dirt, rain, and other contaminants while you work on it.  If you have garage or shop, then that can be a good place to do an engine rebuild.     

4)  YOU NEED THE RIGHT INFORMATION - If you can get a manual that outlines the rebuild process for your particular engine, then this can be a good investment.  A Chilton's or Hayne's manual will sometimes walk you through the process of disassembling, rebuilding, and reassembling an engine.  As has already been mentioned, it is also a good idea to tap into the information available from an experienced person that has already successfully rebuilt an engine.  In part, that is some of what you are doing here by reading this article.  That is a good start.  If you can find an experienced person that knows how to rebuild an engine to personally help guide you through the process, then that can be very beneficial.

5)  YOU NEED TO KNOW WHEN  -  The wording on this might seem a bit odd, but let me explain what I mean by "you need to know when".  You need to know when it's best to rebuild an engine or when it's best to just get another engine all together.  In my own experience, there were times when I was money and time ahead to just forget the idea of rebuilding the original engine and just look for a replacement engine.  For automobiles, there are some different options: 

  • Buy a new engine - This is usually not practical or economical, but sometimes you can buy a new engine that is made available from the factory.  I've seen this more in terms of older V8 engines that people might use in restoring or building hot rods.  Even so, you might find an engine like this is suitable for your pickup or older vehicle.  Places like Summit Racing and Jeg's will sometimes sell new, factory crate engines. 
  • Buy an already rebuilt engine - You can sometimes get rebuilt engines at places like auto parts stores.  You often just need to swap over accessories like pulleys, alternator, water pump, etc from your original engine to the rebuilt engine block.  It used to be that common engines like a Chevy 350 could be purchased rebuilt like this for a relatively low price. 
  • Get a junkyard engine - This is an option that I've used before.  Rather than taking all the time and expense of rebuilding an engine, it can sometimes be much more economical to just find a junkyard which might have a good engine that was pulled from a wrecked vehicle.  A good junkyard will test the compression on each cylinder and have this documented along with the number of miles on a particular engine.  I recently went this route to replace a blown engine in a Volvo that I bought.  If you can't find a local junkyard with your particular engine, then check out eBay.  There are a LOT of places selling used engines on eBay.  Of course, it can be advantageous to use a local junkyard, because sometimes they will offer a short warranty on the engine, and at least you can go back to a local junkyard if you have problems.  If you buy over the internet, you have less options for recourse if you happen to get a bad engine.

Junkyard Engine

Junkyard Engine I Bought to Replace a Blown Engine on a Volvo 850

Regarding eBay, this can also be a good place to find engines that you might need for a lawnmower, motorcycle, snowmobile, or other small engine applications.  Personally, I have purchased a few different small engines this way to replace blown engines on equipment like a lawn tractor.  I had one lawn tractor with a V-twin engine that threw a rod.  Instead of paying for all the parts to rebuild the engine, I was money ahead to just find another good, used engine.  Even if you have to pay for shipping a heavy engine, it will still often be much cheaper to just get a used engine like this.  There is some risk involved this way, because you never know exactly what you are going to get until the engine arrives.  The risk can be offset by the money saved.  In addition to used engines, you can also sometimes find brand new replacement small engines online.

CONCLUSION - For most people that need to have an engine rebuilt, I'd suggest you look into the option of putting in an good used engine.  You will often be money ahead going this route.  With that being said, I will also say that this may not always be the best choice for everyone.  There are other factors besides money to consider.  It can be a very rewarding process to learn how to rebuild an engine and then carry it out to completion.  Most people can not say that they have ever rebuilt an engine, and it can be a great source of satisfaction to successfully rebuild your own engine.  Another situation where rebuilding an engine might be the best choice is when you want to significantly increase performance.  If you want to build a high performance engine, then installing performance parts like: high compression pistons, performance camshaft, stronger connecting rods, and a ported cylinder head is often best done during a complete engine rebuild.  If you decide to rebuild your engine, keep in mind some of the guidelines mentioned above, and try to make your first experience rebuilding an engine a positive one.