[Dr. Zo]

Thanks for all the advice. It looks like I've got to split the cases on this motor after all to see what is going on inside. I'm wondering if there is a bearing seal, is there a rotary vent, and what's the deal with these 3 small holes that are too low. Assuming I can do it, if possible, I'd like to run the rotary vent, and run the vent pipe through the proper vent in the bottom of the engine, get rid of the "steampunk" fitting. I don't think I can really find out what is going on without splitting the cases.

 

[Dr. Zo]

These are the piston tops on my T120R engine. Is it possible to identify them from these top markings? Thanks.

 

[Dr. Zo]

Splitting the cases: So this 67 engine I have has a few problems. One, the 3 small holes drilled in the primary side case are in the wrong position, too low to do what they are supposed to do. Two, the original breather tube, which exits at the bottom of the engine has been plugged, and it looks like the PO put some substance in the pipe so it will need to be drilled out probably. Three, I'm not sure if there is a rotary breather disc on the inlet cam, that is the original breather system. I think the PO thought he could plug this, drill his 3 holes and then have the primary breath out of a vent on the primary oil fill hole.

When I got this engine I didn't think I needed
to take it apart but I think I do now, at least some bits. So the primary cover is off and I just took off the cylinder. So everything inside looks pretty decent, new even. There are barely any wear marks on the cams, followers, and the cylinders and pistons are clean.

My big question is this, Can I take off the primary side of the cases, that is by removing the stator, clutch, duplex chain, etc, and pull the cases apart, without needing to do the same to the timing side? Can I keep the pistons, cams and all in place in order for me to see if the rotary breather is installed? Then I would be able to plug the 3 holes drilled in the sase incorrectly, drill out the original drain pipe tube, and reassemble the cases (all without disturbing the timing side and keeping the cams in place, etc?

This is the second engine I have worked on so I know I am missing something here. If this can't be accomplished correctly then I'll take the whole thing apart.

Thank you for any advice!

 

[Dr. Zo]

Disassembling the engine. So I started to take this engine apart. It looks like some of the parts are good/ok and some are not. Lots of bunged up screws and bolts and some curious stuff too.

First off I’m wondering if I can re-use the pistons. They are clean and seem relatively new and apparently are standard. I don’t have a lot of experience evaluating this. I see on the piston skirts there is some wear and don’t know if this is normal or what. Here are some photos.

 

[Dr. Zo]

Now onto the cylinder. It actually looks relatively new. I measured it with a caliper (I know this is not the most accurate) and it both cam to just over 70mm, which I believe is a standard bore? Also, it looks like the motor wasn’t run much because the cylinder cross hatching is still a bit visible. So I am wondering if this is good to go as is or if I changed rings I suppose I’d need to cross hatch it again?

 

[Dr. Zo]

The primary side case is puzzling. I can see there is no seal on the crank bearing. It has the 3 small holes which are too low. However there are 2 other holes on either side of the crank bearing housing. I have not seen or read about this before and wonder if someone knows about this kind of alteration. Depending on how the rest of the engine is, I would likely seal all these 5 holes up and go to the original rotary venting on the cam and install a crankshaft seal. I appreciate any comments on this!

 

[Flash Nick]

However there are 2 other holes on either side of the crank bearing housing.

Has someone added them to attach a shaft/bearing pusher.

 

[Dr. Zo]

Has someone added them to attach a shaft/bearing pusher.

I pretty sure this is not the case. There is a tool to drive the sprocket on.

 

[Flash Nick]

To split the cases.

 

[Slippery Sam]

The two larger holes have been drilled to accommodate a punch to drive the bearing outer race from the crankcase.

Your pistons are stamped 'STD' - standard, 71mm bore. Your digital caliper is only showing 70.5 mm? You need to measure the bores again in several places.

Pistons and bores look good to me, I'd re-use them, and the rings, as is.

 

[Dr. Zo]

OK. What is this! On the Gearbox inner cover on the bottom, front edge is a fitting that looks like it is a modification. The fitting is also plugged. Does anyone have an idea of what this would have been for? I may have it welded up if it is not necessary. Thanks.

 

[Dr. Zo]

Here are a few more photos. The brass cylinder is what came out of the hole. It was not threaded into the case, just fixed in there with some silicone or black goo. Plus, the cylinder itself was plugged with goo. It doesn't look like a standard item.

 

[Dr. Zo]

OK, so this seems to be a speedo drive hole from an older 63-65 bike.

 

[Dr. Zo]

Left and right crankshaft bearings - Question. I did not realize there were about 3 different bearings for the left and right side of the crankshaft, marked CN, C2 and C3. I didn't realize this when building my last engine, and will have to look through my receipts to see what I installed. Can anyone explain this issue and how one determines which bearing to use in a 1967 T120R engine. My parts book says the part number are E2879 for the main bearing left, and E1591 for the main bearing right. Thanks for any advice!

 

[Dr. Zo]

Transmission main shaft a bit worn. So I disassembled my transmission and it all looks pretty good except for the transmission main shaft. I don't know if this kind of wear makes this unserviceable and would appreciate any comments in this regard. Thanks!

 

[StuartMac]

Hi,

Left and right crankshaft bearings
did not realize there were about 3 different bearings for the left and right side of the crankshaft, marked CN, C2 and C3.

Waited for someone who knows more than me to post but ...

All ball and roller bearings need some internal clearance. However:-

. if the bearing inner race is an interference-fit on the shaft, that'll expand the inner race a little;

. if the bearing outer race is an interference-fit in the case, that'll contract the outer race a little;

. either or both will reduce the bearing's internal clearance, so you start with a bearing that has additional clearance before it's fitted - C3 - then fitting reduces its internal clearance to 'correct' for normal use.

Otoh:-

. if the bearing inner race is a slip-fit on the shaft, the inner race won't be expanded by fitting;

. if the bearing outer race is a slip-fit in the case (there is some external mechanical retention system), the outer race won't be contracted by fitting;

. if the bearing's internal clearance won't be reduced by fitting, CN has the 'correct' internal clearance to for normal use.

C2 has reduced internal clearance before fitting, 'fraid I don't know what'd enlarge a bearing to 'correct' internal clearance?

explain
how one determines which bearing to use in a 1967 T120R engine.

Aiui, Triumph spec'd C3 clearance on twins' main bearings; however, in the case of your bike's engine, that was 55 years ago, the aluminium alloy crankcase castings have both aged and gone through innumerable heat cycles - the bearing housings could be stretched - the crankshaft could be worn.

What you should do is measure both shafts diameters and cases bearing housings diameters with the appropriate micrometers, correct any ovality by machining then take the measurements to a bearing factor, he'll consult charts and mutter some incantations:-

. if you're lucky, he'll hand you the bearings that'll be expanded by your bike's crankshaft and contracted by its cases to normal internal working clearance;

. otoh, if you're unlucky, he'll tell you the shaft diameters are too small and/or housings are too large, undersize shaft(s) must be enlarged by some process (plating?) to minimum diameter x, oversize housing(s) must be reduced by some process (plating? sleeving?) to maximum diameter y then he can hand you the bearings that'll work.

Or you can ignore any of the above that's correct, order E2879 and E1591, hope for the best ... ignorance is bliss?

Hth.

Regards,

 

[Dr. Zo]

Hi,

Waited for someone who knows more than me to post but ...

All ball and roller bearings need some internal clearance. However:-

. if the bearing inner race is an interference-fit on the shaft, that'll expand the inner race a little;

. if the bearing outer race is an interference-fit in the case, that'll contract the outer race a little;

. either or both will reduce the bearing's internal clearance, so you start with a bearing that has additional clearance before it's fitted - C3 - then fitting reduces its internal clearance to 'correct' for normal use.

Otoh:-

. if the bearing inner race is a slip-fit on the shaft, the inner race won't be expanded by fitting;

. if the bearing outer race is a slip-fit in the case (there is some external mechanical retention system), the outer race won't be contracted by fitting;

. if the bearing's internal clearance won't be reduced by fitting, CN has the 'correct' internal clearance to for normal use.

C2 has reduced internal clearance before fitting, 'fraid I don't know what'd enlarge a bearing to 'correct' internal clearance?


Aiui, Triumph spec'd C3 clearance on twins' main bearings; however, in the case of your bike's engine, that was 55 years ago, the aluminium alloy crankcase castings have both aged and gone through innumerable heat cycles - the bearing housings could be stretched - the crankshaft could be worn.

What you should do is measure both shafts diameters and cases bearing housings diameters with the appropriate micrometers, correct any ovality by machining then take the measurements to a bearing factor, he'll consult charts and mutter some incantations:-

. if you're lucky, he'll hand you the bearings that'll be expanded by your bike's crankshaft and contracted by its cases to normal internal working clearance;

. otoh, if you're unlucky, he'll tell you the shaft diameters are too small and/or housings are too large, undersize shaft(s) must be enlarged by some process (plating?) to minimum diameter x, oversize housing(s) must be reduced by some process (plating? sleeving?) to maximum diameter y then he can hand you the bearings that'll work.

Or you can ignore any of the above that's correct, order E2879 and E1591, hope for the best ... ignorance is bliss?

Hth.

Regards,

Thanks Stuart. A lot to think about. I am not a fan of ignorance is bliss so will have to think this through. As usual, you give a lot to think about that I didn't think enough about on my first engine! Thanks for your time!

 

[Dr. Zo]

Cylinder base dowels. On my motor, two of my cylinder stud holes have a cylinder base hollow dowel recess for the dowel that is in the cylinder. I am unsure of the purpose of this setup and would appreciate any comments to explain this. Thanks!

 

[StuartMac]

Hi,

Cylinder base dowels
purpose

Cylinder block's separate from crankcases but you need the block's vertical plane through the centres of the two bores to align with the crank centreline, and the tappets to align with the cam lobes. The dowels are (should be) a very close fit in the corresponding holes in the cylinder base; if everything's been machined accurately, the dowels should ensure the above alignments are closer than could be managed with just studs through all holes.

Hth.

Regards,

 

[Dr. Zo]

Hi,

Cylinder block's separate from crankcases but you need the block's vertical plane through the centres of the two bores to align with the crank centreline, and the tappets to align with the cam lobes. The dowels are (should be) a very close fit in the corresponding holes in the cylinder base; if everything's been machined accurately, the dowels should ensure the above alignments are closer than could be managed with just studs through all holes.

Hth.

Regards,

OK, that helps - and makes sense.