Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Pre-Unit Cam Bushing Question

Happy Thanksgiving. I am looking to start re-assembly of my 1954 T110 engine and was planning on using cam bushings from Kibblewhite Precision Machining in the motor. The original outer bushing has a small hole in the center top. The new ones from Kibblewhite do not have this hole. The new bushings are listed as fitting my year pre-unit engine. Anyone had experience with these bushings and is the missing hole a cause for concern? Thanks.

I think in 50-odd years I have changed those bushes twice, and that’s a lot of engines. I would have to ask why change them? The originals were sintered bronze, no idea what the Kibblewhites are (for the above reason). The special factory tool ( yes, I have one) is a ball pressed through the timing side bush, with a reamer located in the sized timing side to cut the drive side. This relies on the compressibility of the timing side bush. Yes, you need to cut the lube hole too.
Just notches in the bush doesn’t matter, they’re caused by not using the factory assembly tool, and very common indeed.
My advice would be not to change them!

I appreciate the advice but unfortunately the intake side bushing was damaged and needed to be replaced so that's not an option. It would be easy to drill a hole in the new bushing if required. Curious to why they aren't in the new ones if needed. Their website says they are made of certified bearing bronze.

Have you a picture of the damage, and do you have the special tools?
I would buy the original sintered bronze, and if it is just one timing side bush, replace just the one. The sintered bushes hold oil a bit like a sponge, if anything, they need the oil hole less!

the hole isnt there because its easy to drill but hard to line up a pre-drilled hole.

cam bushings these days are a crap shoot, in my opinion. kibblewhite uses high quality solid bronze, not sintered, and they are very difficult to size. hard to get a reamer to bite in the drive side, and the ball goes through the timing side over and over without increasing the size of the hole. ive done it, but it wasnt like the sintered.

some suppliers sell the sintered bushes, like mitch klemph, but they are pre-sized to dimensions larger than what i am looking for. sizing a sintered bush is not hard, but thats not where the market is.

No picture of the damage as the original bushing has already been removed some time back. I would have much preferred to use the original outer bushing if that was an option, but it was not. The bike is a frame up restoration project and has had considerable cobbling done to it over the years. In the scheme of things drilling and line boring a couple of bushings is just another bump in the road on this project.

Thank you for the reply. I figured I probably needed to drill the hole but wasn't sure as most bushings are available with the hole already pre-drilled.

yep drill the hole - also might want more running clearance than the standard stock (sintered) bronze bushings

The reason Triumph used sintered bronze bushings was due to the lack of oil getting to the cam journals

Line reaming may be in order too

hey i forgot

kyle at CBS above has sintered bushes

If the other bushes are still ok, then just changing the one timing side sintered bush would be worth trying, then checking for camshaft fit. The tool that Kevin mentioned is just a steel ball, no alignment used, the factory reamer then just cuts the drive side. A pre-sized bush may well just work, not a lot of cost to find out!

Mick and Kevin pointing toward the original type sintered bushes is no idle personal preference.
You really need to have a sound reason for choosing solid bushes, and the tools and ability to deal with them.

John Healy has posted quite a bit on this subject. In a nutshell, he strongly advised the sintered bushes over solid ones, with the caveat that the bush length and shoulder thickness was carefully checked BEFORE installation.
The reason for this is that the shoulder thickness positions the cam lobes centrally within the case, and the length of the bush must be a few thou less than the cam journal length (or the cam pinion will bind on the case).
John’s warning was that he has encountered bushes from nefarious suppliers that did not match these requirements, and once installed, the problems are difficult to rectify.
He also advised that ball-bearing broaching will not work with solid bushes, as Kevin said, and they will need more clearance, as CBS said.

The original bushes last for many decades and very rarely need replacement.
They store lubricant in their pores and are readily sized by simple broaching with a 0.875” ball to produce the advised clearance of half to 2 thou with a good journal.

It would be worth measuring your journals. If the cams are old, they may well be undersize. If so, by a thou or so, you may not need to broach the new bush at all. It’s worth checking.
I replaced the bushes on my engines without needing any broaching.a couple of times before I even knew of broaching, without problems. Maybe lucky.

If you did opt for the solid bushes, I don’t know how you’d go about line reaming them (as in how to guide the timing-side reamer to the drive-side bush).
I’m sure there’s a way, but it’s beyond my engineering knowledge.
It’s usually the drive side bushes that are line reamed, which I have done.

I have seen "no need to ream" bushes avaiable, but that only saves grief on the driveside. Sintered bushes on the timing side don't need reaming, just broaching.
The drivesde bushes most probably would be happily broached as well, except their closed ends don't allow that option, so they get reamed (and it might as well be line reamed to the timing side bush.

I suspect that if you simply bored or reamed these (sintered) bushes perpendicular to the case parting surface, it would be quite satisfactory.

Just thoughts…

you can use the standard reamer/ball method on solid bushes, although its finicky, difficult, and takes a very long time. but the last time i went looking, i couldnt get sintered bushes in anything other than pre-sized to the far side of the tolerance limits and a bit beyond, iirc. i wanted closer tolerances, but non-sized sintered bushes werent available at that time.

you can eventually work the solid drive side bushes to where you want them, with a lot of care and effort, but the timing side solid bushes dont crush like sintered-- they stretch, and so tapping a ball through them expands the bush as the ball passes through, and then the bush relaxes to its original dimensions. i fussed with the last set i did for a very long time, and eventually succeeded,.

you dont want to use any kind of abrasives, as they embed in the bronze and become a grinder.

but IMO, solid bronze bushes in a triumph cam application is an answer to a question that nobody asked.

I will have more soon

https://www.classicbritishspares.com/products/triumph-camshaft-bushing-reamer-kits

I haven't had to change many cam bushes, but the pre-sized ones have worked for me on the timing side at least.

“you can use the standard reamer/ball method on solid bushes, although its finicky, difficult, and takes a very long time”

You either mean the ball method, or using a reamer?
Whacking a ball through a solid bush dozens of times is unlikely to achieve much, other than perhaps breaking the case. That is not a good way to size a solid bush.

If using a solid bush, you should ream it, if it needs resizing.

I think the sintered bush was chosen for a very good reason, in this application.
It stores oil in its pores so it has lube when the engine has just been started, even after a period of inactivity.
I think it was also very tolerant of crude assembly at the factory (I doubt there was any line reaming there, just boring along with all the other holes).

All the bushes I’ve got from UK suppliers (egTMS) in the the last decades have been sintered bushes, and they have fitted just fine.
Don’t complicate your life with solid bushes.

“you can eventually work the solid drive side bushes to where you want them, with a lot of care and effort, but the timing side solid bushes dont crush like sintered”

Kevin, I don’t understand this. How do you work the drive side bushes?

I agree that abrasives should not go near sintered bushes, but if the op chooses solid bushes abrasives won’t matter (it’s only the porosity of sintered bronze that captures abrasive particles) as long as the parts are cleaned.

There are bushes advertised as needing no reaming. They can only be bushes with the generous amount of ID. It may not matter, you pays your money and makes your choice. Perhaps these bushes are all ready worn out when you install them!

Just thoughts..

Exactly!

Which is why we sell our kit only for sintered bronze bushings

When you install out sintered bushings, you have to size them, no exceptions

The best way IMO