Rebuilding an engine. For the first timer.

AoD

Well-Known Member
Messages
429
Location
Hammondsville, Ohio
In this guide, I'll explain the process of tearing down your motor for a rebuild. The process is very simple, and can be fun as well. Take your time when following the steps to ensure you get a good rebuild out of your engine.

First, make sure you have all the tools necessary, which can be found via your engines manual. I'm including a picture of the HPI 4.6 motor, so you can have an idea of what we're looking at.

The biggest part of having an RC car, is learning how to work on them. Working on the models is half of the fun associated with the hobby. So, by reading this guide, you're getting one step closer to being a master enthusiast. Start by removing your engine from the chassis, and clean it up as best as possible.

Now, the first process is to remove the flywheel assembly. Take the clutch apart by simply removing the clip holding the clutch bell on. Most of the parts should come off rather easily. But remember how they went on, you will need to put it back together before being able to run your engine. You will need to remove the flywheel nut as well and pull the flywheel off, but I usually leave that for a later step in the process. It's easier to turn the motor over when the flywheel itself is still bolted onto the crankshaft.

Now, remove your cover plate, using the tools for the screws that hold it on to the backside of the engine block. Screw number 1427 in my provided picture. Now, when you pull the cover plate off, you will then see the back side of the crankshaft, and the connecting rod.

The next step is to detach the connecting rod (number 1492) from the crankshaft (number 1493). This may take some work, but on most models it simply slides off. Use the flywheel to turn the crankshaft until you find it's correct releasing spot. If it still does not come off, it's time to pull that flywheel nut. Using the right tools, remove the flywheel nut, and the fly wheel. This may loosen the assembly enough where the crankshaft and connecting rod just about fall out of the block. If you still have trouble, you can take the plastic handle of a screw driver and lightly tap the output shaft of the crankshaft. The connecting rod should easily come out, and the crankshaft will simply fall out of the motor.

Once you get this done, it's time to pull the head. Now, this part is easy, but make sure not to mess the shims up (number 1460). Once you take the bolts out (number 1409), the head will come off. Carefully pull the head in an upwards motion and it should slip right off. Now, the motor should really be looking bare.

Now, it's time to pull the cylinder out (number 1488) . Sometimes this can be as easy as taking your finger and pulling it out of the block. Most of the time, you will have to heat the block up to get it to slip out of the block. Don't forget to wear gloves, and be safe with the heat. Getting the block to around 300 to 350 degrees will be sufficient. You make have to work with it a bit, but it should come loose and slide out of the block. Note that there is a cylinder alignment pin on the block, so with the new cylinder, you can't put it in backwards unless you modify either the cylinder or block.

Now, any time you rebuild an engine, it's good to replace the main bearings for the crankshaft. There were no numbers on the picture originally, so I put a red one and two beside them. Pulling number 2 is usually easy, and can usually be done with just a finger. The number 1, or front bearing can be very difficult to remove. Use the same heating technique used for pulling your cylinder to remove this. Sometimes you may have to use a wheel puller, or some other type of portable bearing puller. It can be very difficult, but remember, patience is key.

You've now successfully tore down the engine, and are ready to start the rebuilding process, but wait! Nows the best time to clean the parts you are going to reuse and determine what you must replace. Take the time to clean up everything really nice, and find out what parts you want and need to replace. Here's a list of parts I usually replace when I rebuild a nitro engine.

1. Two crankshaft bearings (use only high quality bearings, remember these motors sometimes exceed 30,000rpm)
2. Piston, Connecting Rod, Cylinder (Can usually be bought in a set, with the piston and connecting rod already together.)
3. Head shims (I always like new shims, they just give a better seal when new)

Now, during reassembly, there's many questions to be asked. I'll simply sum this up by using the method I use to reassemble my own engines.

First and foremost, make sure to put everything back together the way it came apart. Making a nice little list of how things came apart is a good way to reassure yourself that you're putting it together right.

When putting new bearings in, make sure the bearing race and slot is nice and clean. Also, make sure they go in perfectly straight. If they give you a hassle, take a small piece of plastic and then tap lightly with a rubber mallet or another large surface but soft item. Making sure they go in correctly is key, and if done improperly can cause many problems down the road.

Many people have concerns about break in or assembly lube. Usually, I'll take some 5w20 synthetic motor oil and lightly coat parts that will contact each other, such as the crankshaft and connecting rod, or piston and sleeve. You can also use after-run oil, or other light weight lubricants. Make sure you do though, as the initial startup of your motor is crucial to it's lifespan. One wrong contact can cause a world of headaches and a major decrease in lifespan.

Also, when putting the piston into the cylinder, I like to extra coat my cylinder walls with oil, it helps avoid scratching the surface which can greatly reduce power and lifespan as well.

Another main concern is using new products for your engine. Always use new parts when replacing engine parts. A new part will have a longer lifespan then a used one, and will reduce the risk of you having to break your motor open for another rebuild.

One of the biggest questions I've been asked about rebuilding motors is the startup sequence. Simply put, I'll explain what I do.

After a complete rebuild, I'll put in a brand spanking new glow plug. Right before I put it in, I will actually fill the cylinder with after-run oil. I'll turn the engine over 10 or 15 times, then insert my glow plug. I'll then prime the engine, and get it ready for that first startup.

REMEMBER: If you change your piston and cylinder, you MUST break the motor in again. These new parts are just like having a new motor, so they need broken in.

I hope this guide helps you understand the rebuilding process for your nitro powered engine. It's really is a simple and easy to understand process. If you take your time, and make sure to take the right steps in the process, you'll wind up with a strong and reliable engine.
 

GAJ

Well-Known Member
Messages
138
Location
Ontario, Canada
A couple of points, reheat the block to put the new bearings in. Pop the sleeve while the internals are still hooked up by putting the large end of a zip tie in through the exhaust port and rotate the piston upwards.
 

Stripersniper

Active Member
Messages
72
My stock 4.6 has low compression now after 6 galloons, thinking about a rebuild but I don't think it's my best option. My cooling head has 3 broke fins so need that. Add piston, sleeve and bearings and I'm probably within 50 bucks of a new one. Wanting the lrp32 but there on backorder. Any other suggestions? I also noticed on ebay the hpi 4.6 is more than the lrp. Isn't the lrp alot better motor??
 

Jam Racing 1

Well-Known Member
HPISF Supporter
Messages
4,724
yes it is, some guys love their LRP :ercm:
for the price of rebuilding I would go all new engine wise, there are several guys here running the LRP .28 and rave about it's power and speed.
 

Crazyglassguy

New Member
Messages
2
In this guide, I'll explain the process of tearing down your motor for a rebuild. The process is very simple, and can be fun as well. Take your time when following the steps to ensure you get a good rebuild out of your engine.

First, make sure you have all the tools necessary, which can be found via your engines manual. I'm including a picture of the HPI 4.6 motor, so you can have an idea of what we're looking at.

The biggest part of having an RC car, is learning how to work on them. Working on the models is half of the fun associated with the hobby. So, by reading this guide, you're getting one step closer to being a master enthusiast. Start by removing your engine from the chassis, and clean it up as best as possible.

Now, the first process is to remove the flywheel assembly. Take the clutch apart by simply removing the clip holding the clutch bell on. Most of the parts should come off rather easily. But remember how they went on, you will need to put it back together before being able to run your engine. You will need to remove the flywheel nut as well and pull the flywheel off, but I usually leave that for a later step in the process. It's easier to turn the motor over when the flywheel itself is still bolted onto the crankshaft.

Now, remove your cover plate, using the tools for the screws that hold it on to the backside of the engine block. Screw number 1427 in my provided picture. Now, when you pull the cover plate off, you will then see the back side of the crankshaft, and the connecting rod.

The next step is to detach the connecting rod (number 1492) from the crankshaft (number 1493). This may take some work, but on most models it simply slides off. Use the flywheel to turn the crankshaft until you find it's correct releasing spot. If it still does not come off, it's time to pull that flywheel nut. Using the right tools, remove the flywheel nut, and the fly wheel. This may loosen the assembly enough where the crankshaft and connecting rod just about fall out of the block. If you still have trouble, you can take the plastic handle of a screw driver and lightly tap the output shaft of the crankshaft. The connecting rod should easily come out, and the crankshaft will simply fall out of the motor.

Once you get this done, it's time to pull the head. Now, this part is easy, but make sure not to mess the shims up (number 1460). Once you take the bolts out (number 1409), the head will come off. Carefully pull the head in an upwards motion and it should slip right off. Now, the motor should really be looking bare.

Now, it's time to pull the cylinder out (number 1488) . Sometimes this can be as easy as taking your finger and pulling it out of the block. Most of the time, you will have to heat the block up to get it to slip out of the block. Don't forget to wear gloves, and be safe with the heat. Getting the block to around 300 to 350 degrees will be sufficient. You make have to work with it a bit, but it should come loose and slide out of the block. Note that there is a cylinder alignment pin on the block, so with the new cylinder, you can't put it in backwards unless you modify either the cylinder or block.

Now, any time you rebuild an engine, it's good to replace the main bearings for the crankshaft. There were no numbers on the picture originally, so I put a red one and two beside them. Pulling number 2 is usually easy, and can usually be done with just a finger. The number 1, or front bearing can be very difficult to remove. Use the same heating technique used for pulling your cylinder to remove this. Sometimes you may have to use a wheel puller, or some other type of portable bearing puller. It can be very difficult, but remember, patience is key.

You've now successfully tore down the engine, and are ready to start the rebuilding process, but wait! Nows the best time to clean the parts you are going to reuse and determine what you must replace. Take the time to clean up everything really nice, and find out what parts you want and need to replace. Here's a list of parts I usually replace when I rebuild a nitro engine.

1. Two crankshaft bearings (use only high quality bearings, remember these motors sometimes exceed 30,000rpm)
2. Piston, Connecting Rod, Cylinder (Can usually be bought in a set, with the piston and connecting rod already together.)
3. Head shims (I always like new shims, they just give a better seal when new)

Now, during reassembly, there's many questions to be asked. I'll simply sum this up by using the method I use to reassemble my own engines.

First and foremost, make sure to put everything back together the way it came apart. Making a nice little list of how things came apart is a good way to reassure yourself that you're putting it together right.

When putting new bearings in, make sure the bearing race and slot is nice and clean. Also, make sure they go in perfectly straight. If they give you a hassle, take a small piece of plastic and then tap lightly with a rubber mallet or another large surface but soft item. Making sure they go in correctly is key, and if done improperly can cause many problems down the road.

Many people have concerns about break in or assembly lube. Usually, I'll take some 5w20 synthetic motor oil and lightly coat parts that will contact each other, such as the crankshaft and connecting rod, or piston and sleeve. You can also use after-run oil, or other light weight lubricants. Make sure you do though, as the initial startup of your motor is crucial to it's lifespan. One wrong contact can cause a world of headaches and a major decrease in lifespan.

Also, when putting the piston into the cylinder, I like to extra coat my cylinder walls with oil, it helps avoid scratching the surface which can greatly reduce power and lifespan as well.

Another main concern is using new products for your engine. Always use new parts when replacing engine parts. A new part will have a longer lifespan then a used one, and will reduce the risk of you having to break your motor open for another rebuild.

One of the biggest questions I've been asked about rebuilding motors is the startup sequence. Simply put, I'll explain what I do.

After a complete rebuild, I'll put in a brand spanking new glow plug. Right before I put it in, I will actually fill the cylinder with after-run oil. I'll turn the engine over 10 or 15 times, then insert my glow plug. I'll then prime the engine, and get it ready for that first startup.

REMEMBER: If you change your piston and cylinder, you MUST break the motor in again. These new parts are just like having a new motor, so they need broken in.

I hope this guide helps you understand the rebuilding process for your nitro powered engine. It's really is a simple and easy to understand process. If you take your time, and make sure to take the right steps in the process, you'll wind up with a strong and reliable engine.
Thanks man,
 

spanglyyetti

New Member
Messages
1
So I have a SS 4.6 that has sat around a long time and has the piston seized in the sleeve. Have tried numerous things to free in the hopes of rebuilding it. Nothing has worked so far. Ideas? Or ditch it? Also in the possibility of ditching it is there any modifications needed to make LRP 32 fit? Will the stock clutch and bell housing adapt right into it. Thanks
 
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