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Stripping The Free Engine

Blog Date - 21 January 2018

I've stripped and rebuilt the freebie engine I received as mentioned in Engine For Nowt   

The free CPI 125 engine on the bench ready to be stripped down
Right then - let's be at ya

I'm glad I did. 

Taking the cylinder head off was an absolute doddle because this is a copy of the CG125 engine that has pushrods. Hence there is no camchain to lose, no timing to note and the 2 valve system is incredibly simple. So simple in fact it makes me wish the CBF125 also had pushrods. I understand the mechanical advantages of an overhead camshaft system but oh my - pushrod top ends are so easy to work on.

The valvetrain on the engine is operated by pushrods
Simplicity is a thing of beauty. Just nuts and bolts.
The followers of the camshaft are in the barrel of the motor
Simple and effective. If it ain't broke don't fix it.

The next thing I needed to remove was the flywheel. Dammit! I tapped and whacked and wobbled and pulled all to no avail. I need a flywheel puller. Latchy has rebuilt a CG125 and he has a puller - great! The only thing is this flywheel is not the same as the original CG125 it seems. 

The flywheel on the engine that refuses to budge
Right how about just falling off like a nice flywheel huh?

I need a bolt. I get a bolt from my collection but the threads are wrong. After waiting several days due to the curse that is employment I eventually get myself down to the local bolt shop and get a M16 fine bolt. It threads in but despite my hammering, wrenching, heaving and yanking the flywheel is still stuck.

I get out the beast, the monster, the cheap Silverline plug in impact torque fiend. "Rat rat rat rat rrrr whizzzz!" and its off. Why oh why oh why did I not do that in the first place?

The removed flywheel and the bolt used to remove it
You thought you'd got awa didn't you? Feel the wrath of my cheap torque monster!

I keep the thread chomping beast out as now it's time to remove the really really tight clutch basket nut too. Erm - nope. The clutch basket is held in place on the splines with nothing more than a circlip. 

The crankcase halves come asunder with ease and I take the time to take lots and lots and lots of pictures of the gearbox as I take it apart. A washer here, a gear there, a circlip here and a dog there - it is way too easy to muddle all this lot up.

A collection of the images takesn while stripping down the gearbox
So that goes there...followed by the washer...then the selecter fork.........I think.

The crank is knackered. The bearing between the bottom of the conrod and the crank is stiff. I loosen it up but the amount of play is excessive. The piston looks a little scored too. The oil in the motor was black and there certainly was not as much as I'd expected in there. This all leads me to believe this motor was brutally assassinated by a "yoof".

The piston shows some vertical scars
It's not a disaster but it looks unloved.

Of course none of this matters as this engine is for display purposes only. As such now I've got all the tight bits loose I put it all back together. Badly. I've missed a bearing from the gearbox. I've cocked up the timing from the crank to the camshaft. In doing so I have learnt an important lesson.

The bearing that should be inside the engine is outside the engine
Erm. Yeah. I'll - erm - put that back in when I'm stripping it at the show huh?

If ever I am to rebuild another engine I shall do it at least twice. Why? Because practice makes perfect. It is right to note where everything goes. It is correct to take lots of pictures to look back on as reference. But there is still no substitute for having done a job a few times to know that you're finally doing it right.

Oh - and if I'm ever going to get the gearbox back to how it should be I am going to need a diagram. Sometimes pictures are just not enough.

We're always on the look out for good content. If you have a motorcycle related tale then contact ren@bikesandtravels.com

Reader's Comments

Ian Soady said :-
"The bearing between the bottom of the conrod and the crank is stiff."

It's called the big end old chap......

And you would never "loosen it up" as this is one of the most critical bearings in the engine.

I'm assuming a plain shell type bearing with detachable big end cap? If its's a built up roller type bearing as on my old Brit singles then replacing these is a job even I wouldn't tackle as it needs a 5 ton press and measuring equipment I just don't have.
22/1//2018 12:15:50 PM UTC
Ren - The Ed said :-
Yes Ian - the big end. But not everyone reading this will be quite so well informed.

It is a roller bearing in a pressed up crank. When I first stripped the motor is was seized up but I have loosened it. Not with the intention of putting it back on the road because that bearing and the associated surfaces will be cream crackered. I loosened it in case someone wants to see how a crank works.

I would never rebuild a crank like this simply like yourself I just don't have the tools or the skills. I could purchase a crank quite cheaply (£57) but as I have no intention of using the motor in a bike - why bother!
22/1//2018 12:54:45 PM UTC
CrazyFrog said :-
That's not a simple top end Ren - it's one of them there complicated four stoke thingies with valves and stuff! If you want simple, strip a proper bike engine like an MZ two stroke ;)
22/1//2018 1:37:46 PM UTC
Ian Soady said :-
As someone once said "those people who never have time to do it right first time always seem to have time to do it again". Or something like that.

And he's not having my Arrow to practice on - he'd probably forget about the ring pegs and break the rings.......
22/1//2018 3:27:34 PM UTC
Ren - The Ed said :-
2 strokes! Pffffffft nasty horrible smelly petrol guzzlers.

Some of us have to learn things the hard way Ian. Some of us were not blessed with skills, patience and "the nack". Some of us have to struggle and try and try again. It's not easy being stupid.
22/1//2018 4:33:28 PM UTC
Bob said :-
The best advice I can pass on after my years of fettling is this - if you don't have the right tool, stop until you get it!

That old myth about being able to pop off a flywheel with a lump hammer and a screwdriver is just that - a myth. If you did get if off that way you'd probably end up with a bent crank.

Patience is also key, I'm a little short tempered to be a professional mechanic - I sometimes end up beating things to death with a sledgehammer!

Just yesterday I completed stripping my spare G650X Country, it was a complete and utter pig dog of a job, at one point I was so cross with it that I took a picture and went right through the process of listing it on EBay as an unfinished project for £100 (it owes me £2500) just to be rid of the evil pile of junk, but I must be learning because I decided to sleep on it and in the morning I had a new idea to try.
I have never worked on a bike with so many rounded off screw heads and seized threads, it was a trial of endurance, it was emotional. At times I wondered if I was doing the right thing to strip it, but by the end I was enjoying myself because I thought "yes! I've killed you, you evil heap! I've won!"
Takes a deep breath..... The biggest problem was that the Jesus bolt which holds together three seperate rear frame sections and clamps the back of the engine was seized. It was an allen head, it was seized in at the other end (thanks BMW for leaving it open so that corrosion can get in) and the head just splayed open like a daffodil when I applied some torque. The head was recessed some 50mm down a hole so there was no chance of getting to it. Check mate. Then I searched Ebay and found that the right hand section of frame into which the bolt screws was available second-hand. I ordered one and reached for the angle grinder. You should try cutting through your motorcycle's frame with a grinder, it's cathartic, scarey and very satisfying. Anyway, job done - I chopped it through and the whole plot literally fell apart at my feet.
The G650X frame is made up of 5 seperate parts just bolted together, very weird. But I suppose that's the key to it's 141KG dry weight, these frame pieces are remarkably, astonishingly light.
There, I've unloaded now, I feel better.
24/1//2018 8:56:29 AM UTC
Ren - The Ed said :-
Ian Soady? Angle grinder...frame?

I think you made a very acute observation Bob. "Patience is also key, I'm a little short tempered to be a professional mechanic..." Some of us are born with patience. I suspect the likes of Latchy and Ian are the type of people who can look at a job and say "yeah, this will take a while, will need to be planned, will need to be carried out methodically and in detail." Then there are people like myself and perhaps yourself who look at anything that will take more than 2 hours and go "I've lost interest already."

I have LEARNT patience. I know it is required and the advantages it brings. As I age I also find it that little bit easier to find. However it is not natural within me and it does not come easily.

What's the plan with the G650Xs?
24/1//2018 1:32:57 PM UTC
Bob said :-
The best mechanic I know has a Zen Master-like ability to stay stone cold calm at all times, it's amazing to watch, but I am not like that.

I bought the XCo because it's the best bike for me, powerful and light weight. Then whilst idly browsing T'evilbay another one came up at good money, I felt flush that week so hit the button. On receiving the second one it was obviously a bike that had seen some action, I started to work on servicing it and sorting it out but the deeper I went the worse it got - nothing actually wrong with it mechanically it ran and pulled perfectly well - it was just all the mismatched and chewed fasteners, most of which proved to be also siezed in position.
So I found myself looking at a mountain of work to bring it up to spec, or a few days work to strip it down and shove it in the loft, I went for the second option.
I've done it before, I rebuilt an FX650 and KLX250 from storage boxes (having previously stripped them myself) and it was fine.
I've only really got room for three bikes and with the TDM850 & XR125L I was tripping over myself with the two XCo's.
It's just the way I do things, XCo no.2 is now a spares mule for XCo no.1 and I hope that I've got enough now to run them until either we're not allowed to operate internal combustion vehicles any more or until I get bored with it (far more likely).
24/1//2018 3:20:55 PM UTC
Ren - The Ed said :-
Calm at all times you say Bob? The last person I knew like that was perpetually stoned.
25/1//2018 10:22:20 AM UTC
Ian Soady said :-
Did I hear my name mentioned?

True, in most cases I would prefer to plan what I'm going to do in excruciating detail. However, sometimes you need to go through an iterative series of prototypes to get the desired effect. An example was the valve lifter on the Sunbeam which took me 3 goes to get right - mostly because I didn't have the ability to forge the blank or to do any machining that wasn't possible in the lathe. My final product wasn't as pretty as what would have come out of Wolverhampton but was serviceable.

And sometimes of course my cunning plans turn out to be impossible in the metal.

As for Bob's solution it sounds perfectly reasonable although I wonder why he couldn't drill the bolt out?
25/1//2018 4:01:38 PM UTC
Ren - The Ed said :-
So it's OK for you to take 3 attempts to make a serviceable but unsightly valve lifter then I'm criticised because I need to practice an engine rebuild! Pffffft. And you have the audacity to call my DIY handguards ugly. Double pffffft!

I did wonder why Bob didn't drill the bolt out. If the used sub-frame was very cheap then what the heck, cut it and hack it. Over to you Bob.
25/1//2018 4:29:13 PM UTC
Bob said :-
Exactly - the replacement subframe was cheap and I took the decision that my time was worth more than the cost of it.
The decision was also informed by several reclamations of SLR/FX650 suspension linkages - this involved trying (and failing) to drill the end out of a 10mm diameter high tensile bolt, a very similar scenario to that which the BMW presented. The solution in the case of the SLR was aslo the angle grinder.
Add to that the fact that by then I was so cheesed off with it that I relished the chance to attack it with the disk of death!
26/1//2018 9:31:40 AM UTC
Liam said :-
I did a full bearing overhaul on an 1978 CG125 about 4 years ago. The bits of exhaust valve in the bottom of the engine were a nice find.

It felt odd handing over a fully built ready to go engine to someone who had to simply put it in the bike and go. It's still going now which is nice to know.

Damn good engine them old beasts.
26/1//2018 12:55:46 PM UTC
Ren - The Ed said :-
Aaaah Bob - such happy memories, the good old siezed in linkage on the SLR650 was a joy to behold. I did not realise that rust and crud could work better than any weld known to man. I propose a revolution in ship building - just cover the seams to be welded in 20,000 miles of motorcycling muck and leave to set for 3 years. Job done.

I know the CG motor is a good 'un Liam. What I don't know is how well the CPI motor is made. I won't be getting the chance to find out either. Oh well.
26/1//2018 6:41:12 PM UTC
Borsuk said :-
Ren, if you ever build a boaty let me know the name so I can make sure I never sail on her. :-)
26/1//2018 8:12:01 PM UTC
Ren - The Ed said :-
Dammit Borsuk! I was counting on you being the captain.
26/1//2018 9:56:34 PM UTC
Borsuk said :-
Not sure whether to be chuffed that you would want me as skipper or terrified that you believe we have equal levels of insanity.
Though after the ride to Settle I have to admit you have a good idea of my sanity level.
26/1//2018 11:06:52 PM UTC
Ren - The Ed said :-
Settle? I was but a mere light shower boy! Look you are the captain by default because you're the only one with experience at sea. I've been on a few ferries but I don't think that qualifies me as an experienced mariner.
28/1//2018 9:14:08 AM UTC

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