Restoring & Modifying 1971 OIF TR120

[NM Bonny]

Okay, well I had an expectedly quiet afternoon, so got after it!

The skinny O-rings clearly weren't doing the job, and I had an awful time with the fat ones, which kept flopping around and shifting out of place. So, I did what a guy on 'that other forum' said he's been doing for many years: just used flat gaskets with a bit of sealant on them.

Voila. Engine stopped racing and--although the tachometer may be reading a little high--I got her settled down to what sounded like a reasonable idle before it started to get too dark to have the garage door open (mice will dash past you and cause sleepless nights).

I'd like to do the strobe timing to eliminate that from the equation re: any misses I might detect, then see if I can get the idle and low speed mixture acceptable for whenever I get the kickstand repaired and can do some road testing of the slide cutaway and needle setting. Hard to do a load test for a good mixture reading of the plugs if it's on the stand...

 

[CarlS]

Congrats on solving the problem. Great work.

 

[Rudie]

The skinny O-rings clearly weren't doing the job, and I had an awful time with the fat ones, which kept flopping around and shifting out of place. So, I did what a guy on 'that other forum' said he's been doing for many years: just used flat gaskets with a bit of sealant on them.

The skinny O-rings should be Amal 622/101, they fit in the small indentation around the exit from the carb into the engine, help to seal when carb is tightened up to manifold or phenolic resin "Insulating block", the latter to stop heat transfer from cylinder head to carb by conduction (vaporises additional fuel causing an over rich mixture).

Neither Amal O-ring nor phenolic resin spacer fitted to 70 on 650 twins because, thrashed, engine vibration through the pre 70 rigid carb-manifold mounting caused the fuel to froth, leading to weak mixture, worst case extra lightening holes in the pistons ...

Fat 70-9711 O-ring between carb and manifold, carb mounted on stepped 5/16" o.d. studs with 1/4"-28 UNF thread, steel cup washer enclosing rubber washer between each 1/4"-28 self locking nut and the carb, if the step is in the correct place on each stud, you should be able to tighten the nuts up to the steps, there should still be a small gap between carb and manifold, sealed by the fat O-ring slightly compressed. The carb-manifold gap stops heat transfer, the fat O-ring and the rubber washers inside the steel cup washers should insulate the carb from enough engine vibration to prevent fuel frothing.

O-rings
had an awful time with the fat ones

Given your posted intentions for riding the bike, imho you would be wise to persevere with fitting the fat ones, for the above reasons. Stick them in place with sealant; if they move when tightening the carb securing nuts (equally), poke back into position gently with small flat screwdriver? When the nuts are tight aiui the gap between carb and manifold should be about the thickness of a business card.

 

[NM Bonny]

The skinny O-rings should be Amal 622/101, they fit in the small indentation around the exit from the carb into the engine, help to seal when carb is tightened up to manifold or phenolic resin "Insulating block", the latter to stop heat transfer from cylinder head to carb by conduction (vaporises additional fuel causing an over rich mixture).

Neither Amal O-ring nor phenolic resin spacer fitted to 70 on 650 twins because, thrashed, engine vibration through the pre 70 rigid carb-manifold mounting caused the fuel to froth, leading to weak mixture, worst case extra lightening holes in the pistons ...

Fat 70-9711 O-ring between carb and manifold, carb mounted on stepped 5/16" o.d. studs with 1/4"-28 UNF thread, steel cup washer enclosing rubber washer between each 1/4"-28 self locking nut and the carb, if the step is in the correct place on each stud, you should be able to tighten the nuts up to the steps, there should still be a small gap between carb and manifold, sealed by the fat O-ring slightly compressed. The carb-manifold gap stops heat transfer, the fat O-ring and the rubber washers inside the steel cup washers should insulate the carb from enough engine vibration to prevent fuel frothing.


Given your posted intentions for riding the bike, imho you would be wise to persevere with fitting the fat ones, for the above reasons. Stick them in place with sealant; if they move when tightening the carb securing nuts (equally), poke back into position gently with small flat screwdriver? When the nuts are tight aiui the gap between carb and manifold should be about the thickness of a business card.

Well, that's frightening.

Question: why wouldn't I just buy a Square-Profile, High-Temperature Silicone O-Ring from McMaster that will sit in the carb's groove--so not squirt around during installation--and provide adequate deck height to maintain the air gap?

Here's a link to that page. They are rated at -60 F. to +400 F., which should be more than adequate on the intake side.

 

[NM Bonny]

Oh, I think I see why they didn't go that route.

The 70-9711 O-ring is ~.1000" and the skinny one--which sits in the groove--is ~.0695". So, a square O-ring which would fit the groove wouldn't stand proud enough to maintain an air gap--though it would definitely seal better than the skinny round-section, due to the broader contact area against the manifold...

However - this O-ring may well work. It's .134" thick so just .004" narrower O.D. than the 70-9711 (essentially identical) but also .0725" smaller I.D. So, it would provide a much broader sealing area than the round-section 70-9711 O-ring.

The only issue, potentially, would be that the groove in the carb flange sort of might keep the 70-9711 aligned--to the extent it gets forced into the existing narrow groove by clamping pressure. But with some ultra gray or Yamabond to hold it in place during assembly, the square-section should stay put long enough to get clamped in place.

Ideally, if there's room on the carb flange for me to open up the groove to receive the square-section silicone O-ring, I'd undoubtedly have a superior seal and far easier R&R procedure.

So: if I'm ultimately unsatisfied with the 70-9711 O-ring, I'll either try the above square-section silicone O-ring or do what I considered early on: (i) dump the Amals (these are brand new and would sell for a good price) in favor of Mikunis or whatever people favor in lieu of them; or (ii) modify the existing manifolds to attach with a rubber sleeve-and-T-bar clamp setup.

 

[NM Bonny]

Yeah.... to the heck with it. I have been futzing with the Amal 930s because they were brand new on the bike when I got it (new cables, too). But as this is just slightly a modified bike and will never be resold, I'm getting Mikunis!

So: these brand new Amals will shortly be listed for sale, with their new cables, new K&N filters with threaded aluminum mouth extensions to hold the filters securely.

I'm waiting for a reply email from the MAP Cycle tech guy re: whether to buy 30mm or 32mm in view of my eventual step-up to the Morgo 750cc big bore kit. But I'm done with the O-ring nightmare and looking forward to Mikuni performance, as I've ridden bikes fitted with them and they really went.

 

[NM Bonny]

Marino at MAP Cycle says 30mm for either a stock cam 650 or 750, so that's what I ordered.

Again: these brand new Amal 930s will now be removed, drained of fuel and wiped down, and for sale at a bargain price complete with new cables, new cup-and-o'ring nut kits, a new set of fat manifold O-rings, and nifty aluminum screw-on throat extenders (see pic) for the new K&N filters I have fitted. I think their slight extra length also facilitates better OEM air box sealing, too...

Please PM me if interested in getting ahead of the listing...

 

[Rudie]

getting Mikunis

K&N filters

Do not fit the Mikunis?

 

[sikatri]

I absolutely love this project. Looking forward to the upgrade carburetor install!

 

[NM Bonny]

Do not fit the Mikunis?

Yeah, I know... the Amals are part of the bike's original aura that I would've liked to have kept. And they are breathtakingly simple. I love the ability to swap both main jets in 5 minutes.

But as patient as I've become with fiddly fasteners over the past 50 years of auto and motorbike tinkering, the thought of messing about with that carb-to-manifold fitting setup by the side of the road in Monument Valley with miles to go before I sleep tipped me over the edge.

Also, the rubber sleeve arrangement solves multiple problems at once: (i) no sealing woes; (ii) no fiddly O-rings and fasteners; (iii) heat and vibration isolation; (iv) no reduction in performance (from what I've read, anyway).

I dunno if the K&Ns will fit the Mikunis, but assuming it doesn't take MAP too long to assemble the kit, we'll soon see--thanks for the suggestion.

 

[NM Bonny]

I absolutely love this project. Looking forward to the upgrade carburetor install!

I'm so glad it's been vicariously fun for you (and others). Its evolving nature--which sometimes has surprised me as much as anyone (like the fairing and rear-sets)--has truly been one of the things that makes me want to get up in the morning on certain days.

But one reason I am planning an interstate excursion (and ideally several in different directions) per another thread is that I'd like to make the shared fun of this unique bike more tangible. POV GoPro videos are pretty neat but not the same as seeing, hearing, and sitting astride an unusual machine in person. Don't you think?

As for the installation: One obvious bit of simplification is the Mikunis' integral choke levers: in losing the OEM choke control, my period-evocative fairing just lost a bit of vintage charm or became less cluttered and more like a '70s works racer, depending on one's point of view...

As I mentioned to Rudie, it's a loss in one regard--but in another way this bike owes no allegiance to any standard, apart from a threshold consisting of mechanical and aesthetic considerations that's hard to define. I don't think a pair of Mikunis crosses that line, which is one of those "I'll know it when I see it" things, if that makes sense.

 

[Rudie]

The emoticon applied to your "getting Mikunis". As a general rule, I do not like to advise expensive deviations from standard if I do not have first hand experience. However, knowing the Amal-Mikuni history, anything posted in forums about Mikunis on old Triumphs says they are a good idea.

Otoh, "Do not fit the Mikunis?" applied to your post that you intend to sell the K&N filters; I wondered if they would fit the Mikunis?

the thought of messing about with that carb-to-manifold fitting setup by the side of the road in Monument Valley with miles to go before I sleep tipped me over the edge.

Ime, once in place, the 70-9711 O-rings do not move, it is the assembly that is the pita.

 

[NM Bonny]

The emoticon applied to your "getting Mikunis". As a general rule, I do not like to advise expensive deviations from standard if I do not have first hand experience. However, knowing the Amal-Mikuni history, anything posted in forums about Mikunis on old Triumphs says they are a good idea.

Otoh, "Do not fit the Mikunis?" applied to your post that you intend to sell the K&N filters; I wondered if they would fit the Mikunis?


Ime, once in place, the 70-9711 O-rings do not move, it is the assembly that is the pita.

I agree re: the first point. However, a new set of Amal 930s with cables is going for ~$600 these days, so certainly I should be able to recover the $340 I spent on the Mikuni conversion kit by selling my 930s--which are new but for three (3) starts and a total of five (5) minutes of running time (if that). There's just no wear on them at all, so someone will get a good discount for lack of the manufacturer's box.

The Mikuni 30mm kit comes with chrome 'pancake' filters, screw-in manifolds, rubber sleeves with clamps, dual cables... the works (see pic), though it looks like I'll have to retain my big locking nuts for the manifolds. So, as to the fitment of the K&Ns, I'll likely use them if they fit, but if not they're brand new as well, so I think they'll sell, too...

 

[NM Bonny]

This looks like a good tuning guide for these carbs... I'm excited to get them on and running.

Now, to fix the darned kickstand... I've now got three solutions in mind and parts coming, either of which I can return.

Option 1: reinforce the above-mentioned repair mount to reduce the possibility of yet another failure where the 1/2" thick lug meets the semi-circular butting;

Option 2: modify the much beefier coped 1-1/4" mount that comes on this universal kickstand (see pics; made in Ohio) to accommodate the OEM kickstand. The maker said he may be willing to sell me just the mount;

Option 3: just use the universal 'internal spring' kickstand (which is designed for custom Harleys, so is more than strong enough for this far lighter bike) and extend the stand's downward end with some 5/8" 1018 steel rod I bought to make a sissy bar for the '51 FL.

The latter option is well within my welding abilities and my MIG's capacity.

In any of these scenarios, I may just pay my machinist's preferred welder to stop by and attach the butting to the frame, unless I can successfully dial my MIG welder down low enough to avoid blowing through the OEM frame's tubing on some practice material... if I can determine the wall thickness of the bike's frame.

No luck finding that data online thus far...

I am slightly reassured by my success in repairing the fuel tank's aft mounting stud on the '51 FL, as I think that metal is thinner than the wall thickness of the Bonny's frame tubes...?

 

[NM Bonny]

..and... no.

Part no. 83-0035 is coped for 1" tubing, not the 1-1/4" tubing that is used on OIF bikes.

So, I'll have to send it back and default to option 2 or 3 from the previous post. Well, or fabricate my own lug, but I'm inclined at this point to use the LedSled piece pictured above, if it'll work...

 

[NM Bonny]

Okay, did some more hunting around and found out that typically old-school motorcycle frames were made from mild steel DOM (drawn over mandrel) tubing. Ordinarily, 1.25" O.D. tubing like that used on the OIF downtubes is .120" wall thickness.

It would be extraordinary, from what I've read, for Trumph to have used .125" (1/8") wall or thicker tubing because it would've had to be specially manufactured. Unlikely in the '70s, I would think.

So, I found (after much searching) a vendor that not only sells the same stuff at a not-too-terrible price for small chunks but also has cheap shipping ($4.47). I ordered a 1' length to practice on, so I'm at $17.46 in materials for the experiment to see if I can avoid paying a welder.

My sense from looking at the LedSled combo butt and lug is that it's probably adequate out of the box because of the dramatically increased wall thickness over the Triumph part, as marked up in the photo to show where these things seem to always tear. The lug basically acts like a lever on the butt surrounding the frame tube, which of course is yanked on by a much longer lever--the kickstand--until the stress cycles do their thing.

However, I could always take a 'belt-and-suspenders' approach and add a 1/8" or even 3/16" thick, truncated diamond-shaped gusset to the forward edge of the LedSled combo butt/lug--with a 'U' cut out to accommodate the frame tube, of course (see 2nd pic, and excuse the cruddy sketching).

That would be massively strong and simple to do--and should allow either the internal spring unit or the OEM Triumph lever to swing forward far enough to lock in place.

 

[CarlS]

Okay, did some more hunting around and found out that typically old-school motorcycle frames were made from mild steel DOM (drawn over mandrel) tubing. Ordinarily, 1.25" O.D. tubing like that used on the OIF downtubes is .120" wall thickness.

It would be extraordinary, from what I've read, for Trumph to have used .125" (1/8") wall or thicker tubing because it would've had to be specially manufactured. Unlikely in the '70s, I would think.

So, I found (after much searching) a vendor that not only sells the same stuff at a not-too-terrible price for small chunks but also has cheap shipping ($4.47). I ordered a 1' length to practice on, so I'm at $17.46 in materials for the experiment to see if I can avoid paying a welder.

My sense from looking at the LedSled combo butt and lug is that it's probably adequate out of the box because of the dramatically increased wall thickness over the Triumph part, as marked up in the photo to show where these things seem to always tear. The lug basically acts like a lever on the butt surrounding the frame tube, which of course is yanked on by a much longer lever--the kickstand--until the stress cycles do their thing.

However, I could always take a 'belt-and-suspenders' approach and add a 1/8" or even 3/16" thick, truncated diamond-shaped gusset to the forward edge of the LedSled combo butt/lug--with a 'U' cut out to accommodate the frame tube, of course (see 2nd pic, and excuse the cruddy sketching).

That would be massively strong and simple to do--and should allow either the internal spring unit or the OEM Triumph lever to swing forward far enough to lock in place.

You never cease to amaze me with your skills.

 

[NM Bonny]

You never cease to amaze me with your skills.

Very kind of you, but it remains to be seen whether I can actually pull this off.

Well, at any rate, I can certainly cut out and weld the reinforcing gusset to the Led Sled piece. Then we'll see if I can master MIG welding thin tubing sufficiently to make the frame repair myself. It'll be a fun experiment! But if I just melt the practice piece, I'll be calling my machinist's expert welder...

The Mikuni conversion kit should be here by next weekend, so I should be rattling the windows again before too long. In the meantime, perhaps I can figure out how many pockets are needed to sew up the cotton duck tool roll...

 

[grandpaul]

Again: these brand new Amal 930s will now be removed, drained of fuel and wiped down, and for sale at a bargain price complete with new cables, new cup-and-o'ring nut kits, a new set of fat manifold O-rings, and nifty aluminum screw-on throat extenders (see pic) for the new K&N filters I have fitted. I think their slight extra length also facilitates better OEM air box sealing, too...

Please PM me if interested in getting ahead of the listing...

PM'ed...

 

[NM Bonny]

The aftermarket kickstand came in and... well, I'm not even sure gusseting this thing along its front edge is necessary. The first two photos compare the thickness of the butting. I'll mull it over but wow...

The third photo shows the length deficit, which would definitely have to be addressed if I were to use the existing unit. I'll have to R&R it and see if the OEM Triumph lever will work, as the lugs are the same thickness.

One nice thing about using it is that I could rotate the 'foot' during welding, so it j-u-s-t cleared my pipe. Of course, I can drill out the adjustment bung on my OEM kickstand to receive a stop screw, too...

You can see that the new unit has a spring-loaded ball that clicks into detents to hold it extended or up during operation. If I were to use the OEM lever, I'd drill the lug (just barely) to receive a pin that I'd weld on to hold the OEM external spring.

Finally, the coping is close if not perfect. I'll adjust it slightly to facilitate welding (can't have any air gap), but first yucky job is removing the old butting and mounded up welding wire the broker slathered on the frame tube...