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#868429 01/08/22 3:54 am
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I'm building a motor with a big bore kit recently purchased from a reputable dealer and am having some strange issues that may be attributed to mis-machining of the barrels.

The main symptom is that once the barrels are on the cases, and the cams' gears are tight, both inlet tappets hit the drive side lobe of the cam. Only the timing side tappet hits the timing side lobe.

After checking, double checking, triple checking all the variables i can think of, it really seems the inlet tappet block bore is off center.

The (new) tappet block is straight, measured to the outside of the barrel skirts with a straight edge off the tabs on the block.

New cam bushings. Everything fits well, with no gap under the shoulder of the bushing in the timing side case. The cams turn really nicely in the bushings with no binding.

With the inlet cam gear loosened .010" and the cam pushed to the drive side, the tappets move separately, with a bit of a scrape feeling through the tappets, but move completely independently at .015", with no scrape.

The inlet tappet block looks a bit off center in the fins, but everything fits on the case studs. I know the machining accuracy can't be judged on the casting, but still, it's off the same way that makes sense for the symptoms.

I had to machine the cases to fit the slightly larger barrel skirts, but that doesn't seem to be the issue as the barrels seem to fit fine on the studs. A bit snug, but goes on just fine with the barrels' holes centered on the studs.

Is there something I'm missing?

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Who made the big bore kit?

Maybe yours isn't the only one with he problem.

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You should be able to measure the centering of the tappet blocks to the inner stud holes, but note that the drive side holes in the barrel are slightly larger than the rest, as they mate up with the alignment sleeves on the studs. Anyway, the inlet and exhaust distances should be the same. The gap between the cam lobes should also be centred on the crankcase tappet holes.

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Yea. I'm hoping someone else has run into this and has a solution other than blindly trying another one...

It's an Aerco 750 kit.

The barrels have been somewhat disappointing. I had to shorten the shoulder on the exhaust tappet block because that side of the barrel flange is .020" thicker. The threads for the head bolts were very rough and needed to be chased to the point of needing a new bottoming tap. The cases needed to be bored out .030" for the barrel skirts.

Any of the things individually are not a big deal (and some, honestly, expected), but collectively are a real pain. If I didn't have a mill and lathe (and a surface plate and a lot of measuring tools), this rebuild would be all but completely impossible. A shop rebuild would be shockingly expensive with all the measuring and machine work.

This much massaging of a new part that is advertised as plug-and-play is worrisome. The bores are seemingly parallel to each other, and perpendicular to the base flange, so (so far) the basic function is correct, but I may be remeasuring everything very soon.

Other variables I didn't previously include are: new LH Harris cams check out ok (as far as journal and lobe placement - lobes even a bit narrower than stock Triumph), barrel base studs are square in the cases, breather disc and spring are correct (problem same with or without), stock reground tappets, new Kibblewhite tappet blocks, a straight edge across the faces of the inlet and exhaust gears lines up perfectly,

The cases were skimmed on my milling machine, but everything was surprisingly nice and square, and a minimum of material (.004" max depth cut) was removed. Most of the material removed was to square up a fore and aft discrepancy, not a side to side.

I really hope it's just something else I'm missing, or at worst, an out of tolerance part that snuck through.

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Yes. The tappet block bore is visibly off center from the casting, and when measured it's about .030" from center, between the nearest stud centers (taking into account the sleeve on one side). The cam lobes are not exactly centered between the case halves, but both are the same and the exhaust tappet blocks/cams have no issue.

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The tappet block should definitely be centred to the studs, so time to send the barrels back!

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Todd- I don't think I'm allowed to post photos here because I don't pay to be a "sponsor", but I will email you an engineering drawing of the cylinder and tappet block locations. There is a lot of stuff I don't sell at my shop because I know that I will be the final quality control and a lot of parts won't make it out the door. Check your email for the drawing. Hope it helps you, Dan

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Yea. That's what I'm afraid of.

Hopefully the supplier will waive the 30 day return window. It was gathering dust while the crank and pistons were at the crank shop getting rebalanced for 3 months.

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In the worst case, you are stuck with the barrels, the lifter bores can be relocated... It will be a project but you do have the tools.. Good luck..


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the tappets fit with just 0.015 camshaft relocation?

can you fit a shim behind the thrust surface of tbe timing side cam bearing , or will tbe cam pinion rub on thecase?

a 0.015 valve spring shim might solvethe problem.


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Or take a little off the tappet. Even saying that makes me cringe, though.

kevin #868528 01/09/22 2:01 am
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Well, yea. the tappets clear the other's lobe, but at approximately 10 rpm. I'm not sure I trust myself to come up with what I feel is safe for the motor (and rider) at 5k+ rpm with a shimmed cam/bearing. I really thought about the shim, and couldn't shake the thought of what happens next time someone goes in there and gets a DPO moment. I don't intend to necessarily own this motor forever.

I'm optimistic that the supplier and myself will come to an agreeable conclusion.

As Hillybilly bike mentioned, yep, I've got the tools should it come down to it. Thanks for the perspective and might actually be cheaper than redoing a bunch of work to the associated parts. Never done an interrupted cut on cast iron before. Hmm....

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Hi ingermanso, Sorry to hear about your woes.

Do you still have stock cylinder you could trial fit & see how it aligns. Then compare tappet block side to flange holes on both. If it's possible to determine cause of fault & photographing problem, it makes it a lot easier to return defective parts. Also the seller can forward photos to vender so show indeed it was not machined correctly.

On the other hand if old cylinder has same problem, you know it's not the Aerco cylinder.

I feel for you. Spare parts that actually fit are a huge problem for us owners. These bikes are very time consuming to work on & any sublet work often takes weeks to months. They seem especially busy during these covid days as owners have a bit more motivation to get the project bikes moving forward with lockdowns & all.
Don


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Probably not relevant, but I noted that you chased the barrel threads - you do know that they are BSCY 26 tpi, not 24 tpi UNF? I got caught out by that one in wanting to change to a stud fixing for the head instead of bolts a la T140.

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Yep. BSC. Thanks.

Gotta find a new bottoming tap. I was really afraid the tap was going to lock up and break off in the last hole!

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Well this is interesting as I just ordered an Aerco 750 BBK for my 70 TR6R, I have the same kit on my 1970 TR6C with Mega Cycle street/ Strip cams and did notice the thicker base flange which was corrected with a set of adjustable PRT's. I did not notice an alignment issue though with the tappet block bores or an issue with the piston clearance. I was already figuring the tappet block area will need some machining so this go around would not need the adjustable PRT's but now will double check the alignment as well.


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Originally Posted by TR7RVMan
I feel for you. Spare parts that actually fit are a huge problem for us owners. These bikes are very time consuming to work on & any sublet work often takes weeks to months. They seem especially busy during these covid days as owners have a bit more motivation to get the project bikes moving forward with lockdowns & all.
Don
Sublet? do you mean a repair business run out of your home garage? Just curious, how many bikes do you work on in a year? What work takes months, do you mean waiting for parts.....Lock downs? must be a totalitarian govt where you live, lol..


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He lives in California. Isn't that now a totalitarian government state?

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To get back to topic, it would be possible to machine the barrels for Thruxton tappet blocks, but that would mean different followers, cams etc. I have this stuff in my stock, but I'm on the wrong continent

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Blown Income, I had heard about piston clearance issues, so I checked that immediately as it came out of the box. Had good clearance. Checked barrel flatness; good, but it was .018" taller than stock. Didn't even think to check the tappet bore placement, since it seems like shooting fish in a barrel (as it were) to get that placement right, but here we are. The .020 discrepancy in barrel base thickness on one side was an annoyance, but no biggie.

TinkererToo, that's a great idea (!), but I don't have any of that stuff kicking around, and just spent a good deal of money already replacing it all. Would be cheaper at this point to make a new tappet block of bronze or iron, if I'm going to adapt something.

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Hi Irish Swede, California is where my Grandparents on both sides moved during the depression in search of work. It worked out good for all of us. Got good jobs & did ok. So I'm used to the political climate. Thing is our location means thousands a day pass through our state for lots of reasons. We have a very diverse population for lots of reasons. The state is very populated so there is easy transmission of any disease that is going around, locally or worldwide. So things are not so simply & many points of view. I'll just give some personal observation from my life where it's at today. Take it for that. My point of view.

Covid is very rear here. I personally have loved ones that perished after catching covid. None that died were vaccinated. I know several non vaccinated people in my greater social circle at church & in the ballroom dance community. Yes, I'm a dancing mechanic. Do country dancing also. We've danced from coast to coast. Too bad I've not had the Triumph out of state. Back to subject, Of all the unvaccinated we know, now all but 2 have gotten covid & several have died. There are now many break through cases of vaccinated friends we know. So far thank God none of the vaccinated have perished. The funeral home down the road from me is quite large. For many months they had refrigerated semi trailer for dead body storage in parking lot. If the diesel engine was running it was occupied. It ran 24/7 for some months. In these unique conditions what are the health regulators to do?? Let it go & have more deaths or lock things down & restrict our free movement. No easy answer is there? When you personally begin to see your loved ones pass & the disease run rampant through your community it changes things. The problem is there is no easy solution. On paper herd immunity is wonderful option. All that catch it will either die or gain immunity. With no vaccine & total freedom to not mask or do what you will indeed is total freedom. We certainly cherish freedom, that is never to be disputed, but sometimes in special times such as a pandemic is it responsible to voluntarily put our freedom & rights to side for the greater good of the nation & world's health?? Not easy is it. The rule makers are damned if they do, damned if they don't.

So back to bikes the lock down meant many were laid off, shortened hours, or working from home, giving more free time for hobbies such as Triumph Motorcycles. It certainly did me & I'm retired! All the dance halls were closed too you know. However motorcycle parts sellers & machine shops are considered essential businesses. So.... even our evil government knew we needed our bike parts during the pandemic!!

Sublet work is repairs, work on the bike you can't do yourself, so you have someone else do that work for you. Cylinder boring. Valve guides, cutting valves & seats, Paint work, etc. I can't do C630 guides or bore my own cylinders. I can't do professional paint job at home. Sublet work can be to some home mechanic like me, or to a real shop like machine shop or paint shop etc. So many bikes were brought out of storage the parts venders sold out, the distributors sold out, the manufactures fell behind on production. They have to be careful about expanding as after this unexpected demand is satisfied they will have to lay off the extra workers & cannot pay for the extra machines to make parts. Gets complicated doesn't it?

Funny how things have panned out in my area east of San Francisco. The businesses that restrict a client's freedom by demanding vaccination & mask wearing have become busy & successful. Patrons have learned vaccinations help, masks work. Do they really? I don't know? Numbers show that to be true, but in patron's minds it is true. They want to do what they feel is safe, so they go to businesses that make them feel safe. That's a very true reality in my area.

One thing that is totally undisputed.... West of the Sierra Nevada & south of the far north of state the weather is pretty darn nice! Allows for riding year round. Sure a little hot in the summer, you have to bundle up a bit in the winter, but sure beats watching TV. I spent the winter in Fort Lenardwood MO. In the Army. I got there the ground was frozen. Me too!! I didn't warm up until spring. Of course then a tornado came through. A few miles from us. We were safe. Next day went to survey the damage. Wow is all I can say. I was speechless. Maybe that's why the population in California is so big. The weather! Hardly ever humid here either. Everything is a trade off, that's for sure. Many points of view, that's for sure.

For sure, never any hard feelings!! Our binding connection is motorcycles. That's way bigger than politics.
Don


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Do you have a spare cylinder to trial fit?
Don


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I do. The old 650 barrel is at a worn +.060", so what to do? Jump to 750!

Spoke to someone at the dealer today on the phone. He quickly mentioned the 30 day return policy, but I'm having trouble imagining anyone being able to turn a complete engine rebuild with any farmed out work in a month. Hopefully it's a CYA scenario that can be overlooked when needed. I filled out an online return form and crossed my fingers. Still optimistic.

Worst that happens is I rebore the tappet block bore just oversized enough to get a centered circle, make and fit a steel top hat into the barrel, then refit the tappet block into the top hat. I'm a little worried about the recess that the shoulder of the tappet block nests into as it seems under the bottom fins. It would be a long bar in a boring head to be able to get in there to perform an interrupted cut. Chatter city...

Maybe a giant t-slot end mill? So many ways to ruin a brand new part!

The thing that has struck me lately is how much I miss my local shop that closed a few years ago. The Internet is not the same as your actual friends that work behind the counter smelling of old tires and exhaust, giving good reliable advice, and talking loads of [***] to your face when you ignore it. RIP Raber's.

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The law is very likely different in the USbut in UK, retailers sometimes try to hide behind limited time period guarantees such as 30 days etc, but they only get away with it with customers who aren't aware of their legal rights. Here, it is the law that goods sold by businesses have to be "fit for purpose" and "of reasonable quality". There is no set time limit on these requirements, though it is usually at least a year and can be a lot longer, depending on the item. In this country these laws come under the Consumer Rights Act. As I say, things may be very different where you are but if you aren't already absolutely sure, maybe it is it worth checking out?


If anything other than a blank space is visible here, something's wrong.
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Sublet to me refers to property leasing and not necessarily services. As an electrician contractor I used the term sub contractor or subbed when I paid others to do excavating, setting power poles etc..Or Farming it out
Dancing? Yes, Rock and Roll 50's style. A Rockabilly steady beat and it's go cat go...
I live in a rural area, other than a mask requirement in certain places at certain times, it is business as usual
In the hot rod car world we called the installation of aftermarket parts as needing TLC, as in Torches, Levers and Crowbars
This is the reason my LSR bikes are made up mostly of modified stock parts.. But big bore kits have been around for a long time so there should be no problems..


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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