This is the first part in our extremely popular video series in which Todd Muller, Head Motorcycle Tech here at Lowbrow Customs, disassembles a unit 650 c.c. Triumph motorcycle engine and rebuilds it. These videos are long, detailed and chock-full of all the little tips and tricks Todd has picked up over decades of working on vintage Triumphs, BSAs, Harley-Davidsons and more both at work and in his home garage. Follow along as he shows you exactly how to rebuild your motor and what Triumph specialty tools to use. You can check out the Triumph 650 Motorcycle Engine Disassembly & Rebuild - Part 2 to continue following along!
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You can read a full transcription of this video below:
Hey, guys, and gals. Todd from Lowbrow Customs here again today. What we're going to do, show you here is we're going to disassemble this 1968 Triumph 650 engine. We're going to do a teardown and what to look for when taking this motor apart in preparation for rebuilding it. This motor was essentially designed in 1937 and debuted for the 1938 models.
It's basically remained very similar in configuration since that time. That tells you that this is a very good engine design if they didn't need to change things. This is referred to as a unit motor. The reason for that is because the transmission and primary are contained within the crankcase as a whole unit, hence the term unit motor. The predecessor to this motor, the one that was designed in '38 was called a pre-unit motor.
The way that worked was the crankshaft cylinder head was one piece and the transmission was a separate piece and then they were joined together by an inner and outer primary, hence the term pre-unit. This is considered a parallel twin because both the pistons rise and fall at the same time as you'll see once we get the cylinder head off and take a look at the cylinder.
Basically, the unit motor for 650 started in 1963 and went up to 1972 as a 650 motor. In 1973, they basically changed the bore size and put a shorter rod and then it was a 750 motor. One of the other differences to take note of is the cylinder heads. The first pre-unit motors had 8 bolts for the cylinder head, four here, four here. When they went to the unit motor, they added a center bolt making it a nine bolt head. When they went to the 750 motors, they added another bolt in the center here and that was considered a 10 bolt.
Basically, if you buy a bike in a box and you're looking for parts at the swap meet, these are some good things to know that you're not buying something that's not going to work with your year range motor. Any of these motors will have a pad on the side of the motor in this location right here that will have the VIN number. You can cross-reference this VIN number to tell you exactly what your motor you're working on.
There's also some differences early too late for the rocker boxes and cylinder head as to the pushrod tubes. Once again, if you're building a motor out of a box, if you might buy the wrong parts and then you have parts you can't use. Basically, there's a recess in the bottom of the head that the push rod tube fits into and the tappet blocks. I'll go over the year changes on that stuff as we go along here.
At any rate, if you want to take a take a look here. We have a VIN number on here and it says T120R DU34708. T120R denotes what model engine this is. It has a twin carb cylinder head that denotes that is a Bonneville engine. If it would have said TR6 on here that would denote a single carb cylinder head. A lot of times over the years, guys switch parts around. It is totally acceptable to put a single carb head on this engine. It will bolt right on exactly the same. You're just running one car versus two. That is essentially one of the main big differences between a T120 and a TR6.
There's also this thing I see a lot on the interweb people having discussions about looking for a single carb head because they think it's easier with one carburetor. In all honesty, it's not that difficult to dial in two carburetors on one of these engines and that the twin carb T120 Bonneville engine actually had a little bit more horsepower than the single carb version of the same motor.
The information for this can be found a lot of places on the internet. We do have a spot on our website where you can take a look at your VIN number. It is always a good idea if you're looking up part numbers that you know the year of the motor. While we're on the subject of VIN numbers, another interesting note about these motors. Pre-'68 did not have this raised pad on the engine.
Basically, the numbers were stamped right into the crankcase, a 68 first year for the pad on the engine. It was just a plain pad with the engine numbers of the year of the model stamped into it. In 1969, the pad continued but Triumph Motor Corporation put a little tiny Triumph logo all across it, Triumph, Triumph, Triumph, Triumph, Triumph, all across the pad.
Basically, I do see a lot of these engines that have been restamped. It was common practice for a dealership, if they were sent a replacement set of crankcases for Joe's motorcycle that blew a rod through the crank, it was up to the dealership to restamp the numbers. It was not up to the other Joe in his garage 20 years later to restamp numbers or letters.
There's also some fraudulent motors out there. People trying to pass off something that that is not really is and it's also not unusual to see the numbers on here going off at an angle or not being straight in line. I think that's because the Brits were at the pub for lunch, drinking some pints, they came back to the factory, and they started stamping numbers. That's just one of my theories.
At any rate, it's not unusual to not see a VIN number that's not perfectly in line or straight. If you see one, that's perfect. That could be a Hokie VIN number. There again, if it has been restamped, you could be looking at parts books that aren't really associated with your motor. The other thing is the motor number and the frame number technically matched at the factory. When they were building the motorcycles, they stamped the same number into the crank on the crankcase as the frame.
There again, you're going to find a lot of bikes out there these days that don't have matching numbers. It's not a huge deal if you're building a custom bike. It's not a big. It's always a good idea that any time you're going to look at a motorcycle for sale that it does have paperwork. A lot of states have different laws regarding how to get a title for something that doesn't have one. You might want to check with your state to see what their rules and regulations.
If you're going to look at a bike and it's just like the best deal ever but it has no paperwork, if you can't get a title for it, you're probably not going to be able to rebuild it and put it on the road. You're kind of throwing your money away so might want to stick it out and wait for a better project to come along. The other thing worth mentioning is it's also important to have a book for your motor. If you're not familiar with these, it'll go over a lot of procedures and how to take things apart correctly without damaging parts.
We offer this book on the website. It's called Glenn's Triumph. This is a really good book in my opinion. Factory books are good but they assume that you know what you're doing and they don't go into great detail on every aspect of engine work. This book has a lot more pictures and a lot more information than a factory book. These are available on the website, a good addition to your garage, regardless of whether you're building one motor or five motors. It's important to have a workshop manual.
Another book that I'll be referencing today during our video is this really cool book that I have here. This book came from the Triumph Motor Corporation. If you were a mechanic at a Triumph dealership and you got sent to school to learn how to work on one of these engines. This is the book they would have handed you when you walked in the door, and for disassembly and reassembly. A lot of good information in this book.
I know there is some digital on the internet you can find this book. There's some really good information in here. If in the beginning of the book it goes over all the year changes for the various different things on the engines. Just to reiterate, make sure you're getting the correct parts for your engine, so that when you get it all back together, everything's going to work correctly.
We have the majority of the moving parts inside this engine that you will need for rebuild on our website. I get a lot of phone calls and customers wondering how to do things. We decided we thought this would be a good idea to go ahead and go through the disassembly. There is a handful of special tools required to disassemble this engine. The rest of its all pretty much basic hand tools. A lot of customers are confused as to the fasteners that were used on these motors.
The earlier motors did have different fasteners where you'd be required to have Whitworth wrenches, that's a British style of fastener. Starting in I believe '68, they started to switch over to SAE but you're also going to find Whitworth and standard American sizes on these motors. Anytime you're disassembling something like this and you want to try to reuse fasteners, it's a good idea to use the correct sockets or wrenches for the job. That way you're not rounding things off and buttering stuff up.
Okay, first thing I'm going to do before we start tearing the motor down is I'm going to utilize Lowbrow Customs Triumphs 650 motor stands. Have these available on the website. They do not come with any bolts so you need to run down to your hardware store and get yourself a four-and-a-half-inch long 7/16 bolt and a six-inch long 5/16 bolt.
Go ahead and take this out of the box. Will show you what she looks like. This will make your life much easier when breaking fasteners. See, how this motor is wiggling all around there. This will keep it a little more stable, make it easier to work on and we'll be able to utilize it until it's time to split the crankcase. There she is, gang. This is going to go through the poll on the bottom of the crankcase and this is going to go on a fastener we're going to take off.
Okay, in order to attach the engine stand to the engine, you're going to need to take out this crankcase bolt right here. Incidentally, it is Whitworth. This is threaded on both ends. You don't have to take the nut off both ends. You should be able to slide it out once you take one side off. Another practice I like to do is I'm taking engines apart as I am in the habit of putting things back where they belong.
In other words, I'm not just throwing all these fasteners in a box and then trying to find them later. While we're on that subject, what I like to do is I go down to my local liquor store and I get some of these cut-down boxes. These are absolutely perfect for putting your parts in as you're going along. You can keep things organized. Now, you can put like all the primary parts in one box, all the tiny parts in a box instead of having a big pile all over the workbench.
We'll make this one engine bolts and such. Go ahead and get our stand on there. Now, I'm just going to lay this thing over on its side because I think it'll be a little easier to get the stand on like that. Not going to hurt anything. There's a nice shot at the bottom of the engine. I think it might not be a bad idea to take these oil lines off of here right now. Well, I can get to them a little easier.
Sometimes when they been down there for a few years, they don't want to pull off. Took a razor knife and cut through that line. This one, these are your feed and return lines going to your oil pump from your oil tank. We will talk about which ones which a little bit later on. Once we get some more stuff taken apart, it will be easier to see how this attaches to the engine.
There we go. It's also a good idea if your motors really greased out. Fold it out of the chassis and it's just caked with grease, it's a good idea to clean it before you start disassembling it. This one's not too shabby. Okay, so engine stands. Larger bolt go right here. The longer 5/16 will go on the front. Another nice feature on the engine stand, it does have four holes if you'd like to bolt it down to your workbench. Well, of course, then you have to pick the engine up to set it in there which is a little bit more awkward in my opinion.
Now, we have the stand on there. We can go ahead and set this up and see how easily that will move around on the bench for working on it. That's why I'm not going to bolt this down to the workbench because see how easily I can spin that motor around to go from side to side to work on things. Okay, the procedures I'm going to show you here are also going to apply if you're just doing a top end, because I'm going to take the top end off first.
If you were to pull this motor out of the frame, it would be to your best advantage to remove the rocker boxes before removing it from the frame, because it's very difficult to get it out of any of the frames from '63 to '69 had a welded portion on the front and motor plates on the back and it just doesn't want to come out of the frame where the rocker box is on. For the video here, we do have the rocker boxes on. Does look like everything's torqued.
I don't know how it came out of there but at any rate your top engine stays are attached to those four points. It's just really a bear to get it out of the frame so do yourself a favor and what I'm going to show you next about taking these apart will also apply. If it's in the frame, you're going to take these two pieces off first. Okay, first thing we want to do is we want to take these caps off. This is where you would be doing your valve adjustment.
Notice how it has these little chingas on here. If you notice, there's a little nub on that chinga and there's a serrated edge here. Basically, these don't have to be tightened until the cows come home. They do have a seal. When you tighten that, that little chinga keeps that from spitting off of there. See that, it doesn't want to turn now that I tighten it down. If they're really tight, a little trick you can do is you can take a standard screwdriver and just stick it under there and lift it up a little and that will let you -- or you can just take these out. There's four Phillips head screws. You can just take these off and then unscrew these.
Like I said, these shouldn't be overly tightened. You might be able to hear on the video there how that was kind of making its little noise on there, right there as it's coming off. It's a good idea to unload the valves. If you want to de-adjust them, there's a larger nut and you're going to loosen that. Then there's the center square nut. Actually, these are both turning at the same time. Basically, I'm taking away the valve adjustment. That way when we take this off, it won't be pushing against it while I'm loosening.
Now, notice how this, this rocker's down, that means it's opening this exhaust valve. What I'm going to do is I'm going to grab an old kick-starter. I'm going to rotate the engine so that these both valves closed. I'm going to go ahead and take the spark plugs out because it will turn over much easier with the plugs out.
That one seems a little tighter. There we go. If your spark plugs real hard coming out, there's a chance the threads might be stripped in the head. That's one of the inspection things you'll need to do. There we go. Okay, so I was going to turn the motor over to open this -- or I'm sorry make this valve closed so that I could de-adjust it. What I discovered, I grabbed an old kicker and put it on there and tried to turn it, smother stuck. It doesn't want to turn over.
That's something else is very common when you buy a motor to swap meet or even when you drag a bike home. If it hasn't been running a long time, it's possible that the motor doesn't even turn over. More than likely what we're going to find is that the rings are stuck to the cylinder is very, very common on these motors when they've been sitting around for a long time and not being turned over.
It really won't hurt anything. It is a good idea to unload those. It's not going to be the end of the world if it's stuck. We can't unload them, so we'll just go ahead and proceed with taking the rocker boxes off. Okay, I really wasn't aware that this motor was stuck. It's been sitting over there on my side workbench for a very long time. One of the things I do very frequently when I bring home a motor from a swap meet or a whole motorcycle.
If the motor stuck like this and it doesn't want to turn over, what you could do to help it is this product here, it's called Marvel Mystery Oil. It's available at just about any auto parts store. It's not going to come in a water bottle. My container broke so I put it in here. This stuff's been around forever. Very good stuff. I'm basically just going to dump some down the spark plug holes so as we proceed here, that will give it a little bit of time to soak.
If you find an engine like right now, I can look down the hole and see the pistons pretty far down there. It would have been a better idea to do this two weeks ago to see if it would free up. Now, before we start disassembly but we will get it apart. You're just going to be generous with it. Put some down in there. Another thing about Marvel Mystery Oil, you can put this stuff in your oil. You can put in your gasoline.
I very often tell customers that call about tank coatings, I will tell them that if they just bought a raw tank from us that's bare steel and they're mocking up a bike and they don't plan on using it for quite some time. I'll tell them to put some of this in the gas tank and slosh it around to coat the interior of the gas tank and that will stop it from flash rusting. Then when you do go to put the tank in service, you can just put your gas right in with this and it won't harm your engine. Add the gas or oil if you do end up getting some from the parts store and read the label you'll see really good stuff. I highly recommend it.
Okay, in order to get the rocker boxes off. You're going to need to take the four center head bolts off. These two still have the nuts on there from the engine stage that are connected to the frame. We'll go ahead and take those off. There's going to be four head bolts. Three smaller nuts on the bottom here and four longer bolts right here. We'll go ahead and break the head bolts first. Not super-tight.
it is highly possible that the person that pulled this motor out had these off of here. Not super tight at all. As you're taking these head bolts out, if they're hard going the whole way, that means there may be an issue with the threads on the cylinder. These came out fairly reasonably easy, no problem there. Okay, we have four fasteners here. I'm going to go ahead and take some of the smaller ones out next. The nuts off the bottom.
Don't be alarmed if the entire stud comes out of the rocker box with these. That's easily fixed when on reassembly. It's common. These are all coming off with no problem. That's a good thing. Once again, four head bolts, six smaller nuts on the bottom. Now, all we have left to do is take out these four here. Notice how that's coming up because it's still under load. Once we relieve the pressure on there, we're going to go a little bit like even side to side. Should be okay.
That's all there is to taking that off. Well, that's looking very clean in there and fresh grease on the pushrod tubes, very suspicious. Another reason for taking these motors apart when you don't know their history is you just don't know what you have going on in there until you take a look. A few gaskets are way cheaper than not knowing that you have something bad inside your engine.
Okay, we'll talk about those in a sec here. We'll go ahead and take the rear rocker box off. Also, there's some very skinny little washers that fell off that go on here. Go ahead and put those back on there. It appears that one may be stuck on the bottom of the head. Yes, there it is. Just pay attention to what you're doing as you're going along. Like I said before, it's not a bad idea to put things back where they belong. That way small things like this don't get lost.
Okay, there it is, rocker boxes are both off there's. There's one of my washers. There's one. That one has run away from home. Okay, now you can see I like to take my gaskets off as I go along too. It's always a mystery what you find inside these motors. It's actually fun taking them apart. I really enjoy this kind of stuff. I'm seeing a pretty new-looking gasket. I'm seeing fresh grease which the motor had been in service. It's a practice to put grease on there when you're assembling it. We might just find some good things in here and we might just find some bad things you just never know.