Tl125 Advice Needed.

[mach4man]

Apologies if this has been covered anywhere before, but I'm new here.

Have just come by a TL125 project.

The engine and frame nyumbers relate to a 1973 bike but it has a 2 piece head fitted.

Also, currently fitted inthe bike is a CB100 engine complete, also with a 2 piece head.

The cam bearings in the TL motor are goosed, but the CB seems fine.

My question(s) are.

Is it OK to fit the 2 piece head type 124cc top end on earlier 122cc engine?

This engine had a problem many years ago, could the fail be down to mis matched parts?

If you can mix the barrels will it be OK to use the CB100 head on the 124cc barrel?

Thanks for any advice.

Tom

[maxbikes]

or fit a cg125 engine.it will loose a bit of value,but if your going to use for trials yourself,the cg125 engine far better than tl engine.

[tltel]

Hi.

Its a long time since I played mix and match with these engines but many years ago my mate and I both ran TL's and would try anything to keep them running, and since we had very little money quite often we would take parts off donor engines and rebuild them.

I think you can use the 100 head on the 125 engine the only difference if any would probably be the valve sizes and maybe the cam shaft timing.

The TL cam timing is different to a CB, XL etc so if poss use the camshaft from the 125, that's assuming It is a TL head.

There are different auto advance units too so check every thing before you swap them over.

just an aside but if I remember correctly the cam chains are different lengths on the one piece head, but this obviously will have been changed already.

Most problems on these engines were due to bad oil and not changing it often enough, and I have to admit I was guilty of that too when I was younger....

TLTEL

[craig10]

My question(s) are.

Is it OK to fit the 2 piece head type 124cc top end on earlier 122cc engine? - Yes but you'll need a 98 link cam chain (100 on the 122 engine) and at least the rear tensioner blade off the 124 engine, possibly the front one as well.

This engine had a problem many years ago, could the fail be down to mis matched parts? - Unlikely, the main cause of death is dirty oil or folks taking off the clutch cover to clean the centrifugal filter or whatever then putting some sort of gasket sealer on when replacing the cover. A piece of that then comes off and chokes the 1mm diameter hole that feeds oil up the right rear head stud to the camshaft, then it's curtains. You really need to make sure the oil galleries are spotless where the oil feeds round to that stud, and don't use gasket goo on the casings, the only place it's needed is a very thin film between the 2 halves of the head.

If you can mix the barrels will it be OK to use the CB100 head on the 124cc barrel? - If the pitch of the head studs is the same then maybe but there's a lot of variables. You'll need to check that the combustion chamber is the same volume on the 124 head and the CB100 head, if the CB is smaller then you might end up with too high a compression ratio or the valves running too close to the piston. Also depends on what piston is fitted, the proper TL 124 engine has a dished crown to lower the CR but the CB and XL 124s have a raised crown. As mentioned above, the TL cam has different timings but any of the 2 pc head cams will fit.

The problem is that as TLTEL says, lots of parts were swapped around on these engines back in the day so it's anyone's guess what's in there.

From memory the CB100 engine has a smaller gudgeon pin than the 125 so unless you changed the crank there's not much can be done there.

Also, it may be regarded as heresy but don't rule out fitting a Chinese replica engine, my mate has fitted one into an old BSA frame and it's been totally reliable, they can be picked up for £150 all in with all the electrics included.

Craig

Edited September 24, 2013 by craig10

[mach4man]

_{Thank you gentlemen.}

_{Some good pointers there.}

_{Have so far removed tp end of the 125 engine, got 56.5mmm bore with no measurable wear, and a dished piston, and broken rings!}

_{So it looks like a standard TL set up. A hone and ring set should fix that.}

_{Must have the 98 link chain because it was already on but will count the links to make sure somebody did not "wing it " with the wrong one.}

_{Have also split the head, and while the cam and bearings look good, (no scoring at all) the cam is very loose. and the hollow bore was bunged up with gasket goo.}

_{Rather than split the 100 engine to measure combustion chamber volume, I think I'll have a bash at bushing this head, One less motor in bits in the shed is always a bonus too.}

_{Then strip the bottom end and make sure Mr sealant has been too busy down there.}

_{Last worked on one of these back in 1977, when my long suffering SL125 gave up the ghost, but it's all coming back to me now.}

_{Thanks for the help everyone.}

_Tom

Edited September 24, 2013 by mach4man

[tlrider]

The two piece 'S' model head and the one piece 'K' model head engines have completely different cam chain tensioner setups and are not interchangeable. The pivot bolt in the head is in a different location between the two, the tensioners are different lengths and the adjustement mechanisim is different. I started doing an engine with a 'K' bottom end and an 'S' top end a few years ago, I picked up a TLR250 and set the engine build to the side so what I am about to describe is from not to recent memories.

The problem is the longer 'K' tensioner ends up with too much bow in it when atached to the 'S' head. The tensioner puts all of the load on the chain just above the sprocket on the crank shaft rather than somewhere between the two sprockets. When adjusting the tensioner there is so little movement you really get no change in tension. The 'S' tensioner is too short and does not give enough tension. My intent was or is once I get back to the project to thin the 'K' tensioner at the bottom so the contact is somewhere between the sprockets.

[esteve]

Some useful info here:

http://www.twinshock.org.uk/spip.php?article46

and here:

http://www.kaila.net/tl125/tl125faq/index.html

and here:

http://www.trialscentral.com/forums/topic/33454-tl125150-swap/

That will get you started.....

[craig10]

There's a simple fix for supporting the points end of the cam which would get you by for a while, the guy's running it on the road so would last forever on a trialler http://www.thumpertalk.com/topic/724107-honda-single-cam-bearing-solution-why-not/

I did an outrigger bearing on a one piece head a while ago which worked ok but was massive overkill, see here http://www.thumpertalk.com/topic/842366-honda-cam-bearing-conversion/#entry8715919

You might need to register on the Thumpertalk forums to see the pictures

I've line bored a head and fitted a needle roller / ball bearing set up on the cam but not had it running as yet, the engine's in my garage waiting to go in.

Craig

[mach4man]

Does anybody have a camshaft they could measure the journal diameters of please?

I have just been lucky enough to pick up a head off Ebay with "good useable cam journals".

Problem is, when it arrived the cam I have is looser in it than in the head I already had.

In fairness they do look OK, but there is a lot of up and down play at the end of the cam.

Is it possible there are different sizes of cam bearing or I have just been stitched?

I was working on previous advice that all these cams are the same, (apart from profile and timing), be it CB SL or TL motors.

Can anyone help?

Cheers

Tom

[craig10]

The one and 2 piece heads have different journal sizes and are not interchangeable but as far as I'm aware any cam will fit in it's own type of head.

I've measured them as follows

One piece head cam brand new: Journals 29.93 / 19.93 Lobe nearest sprocket 31.95 Lobe furthest from sprocket 31.50

2 piece head cam (used) : Journals 33.96 / 21.96 Lobes (showing slight wear) 31.7 / 31.3

Clearance of journal to bore in 2pc head 0.1mm measured with plastigage, engine was running fine

Check out Vincent Crabtree's stuff in pdf format, there's a whole page on cams http://www.google.co....53899372,d.d2k

Craig

[mach4man]

Thanks for that Craig.

I'll take all this to work on Monday and get everything measured.

Starting to remember while I love 2 strokes!!!

Tom