Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Where do these hollow dowels go?

First to explain why I don't know where they go. I bought two engines for Project 39-1/2. The first one, a '68 650, disassembled, was crappy but I found a nice '72 650, partially disassembled. A few years have passed and I'm assembling the good engine. Sorting through everything and labeling everything. Then I came across this bag of cylinder base nuts and hollow dowels. The base nuts are good. But where do these 4 dowels fit?
They will slide over the cylinder mount studs - but on the cylinder base there is only one enlarged hole that a dowel would fit into. The parts diagram show a hollow dowel #13 (E8751 or 70-8751) and a quantity of one. Why do I have four? Should I disregard the other three? I don't see this part number anywhere else in the parts book.
Thanks
Al

Hi Al, You should have 2 dowels to locate cyl per motor. Look closely, is there a dowel forced up in the cyl base? Which means you’ll have 5 dowels total.

Even the 1973 parts book shows 1 dowel, but there are in fact 2. I’m sure you noticed your crank case is bored for 2.

PM me your email & I’ll send you detailed photos, you’ll see 2 cyl dowels.

I have no ida why Triumuph continues to keep errors in parts books for years. Oil pressure switch is another one. There are several others as well.
Don

That error on the dowels came in 1969 and continued until 1974-75, the co-op finally put it right. Talk about learning quickly. The two studs with the dowels are the inner drive side ones, and as Don says, will often be found stuck in the barrel flange

Apart from the cylinder base, they are also used on the gearbox. Two are are used to locate the inner cover to the gearbox casing and and another two between the outer gearbox casing and inner gearbox cover. The holes where the 3/8" studs pass through have counter-bores to take the hollow dowels.

Hello Shippy, I think you'll find that the gearbox dowels are 5/16" ID, not the 3/8" of the barrel studs. The barrel one was used on the pre-units (with a different part number) as one of the crankcase half locating dowels.

Thanks for these replies. Will head out to shop later. Tinkerer - I looked at the 68 parts book and yep it says quantity 2. Don - sent you my email address in PM.
Al

Interestingly, the 2 studs for the dowels are the same length, but a shorter coarse thread to ‘68, but they didn’t bother thereafter, so you can’t screw the late studs all the way in. Just one of those foibles!

Next question - if I may - the smaller hollow dowel(s) in the timing cover. The '72 parts book states quantity of one. But the cover and crankcase has space for two. Does it use two dowels, and if it uses only one does it go in the forward or rearward hole?
Al

My parts book calls for two (T989) and the blow up drawing shows where they go. Bottom holes of the timing cover.

Thanks desco. I looked in a 68 as well as 72 parts book and they both only called for one. I did try the cover with two dowels and it seemed like it would go.
Thanks everyone. That should keep me busy for a while.
Next task is actually start engine assembly!
Al

My 72 parts book was published in August 1971. Part # 99-0953. I've had it since 1986 and it's pretty accurate.

Hi, Rember certain years with non timed tappet feed, meaning the exhaust tappet oil feed with wide flats on stems, must retain the metering dowel in front dowel hole or you'll have very low oil pressure hot idle.

I've personally experience with only one metering dowel. Visually it looks different with a thick wall & mine was threaded inside for using a bolt as a puller when removing.

This dowel was installed on '69 Bonnie with timed tappets. It effected the oil feed to PRV on this motor. Cold oil press was over 100#. Hot pressure at 4000 rpm was right at 100#. Installing the proper hollow dowel, pressure returned to the expected pressures. 17-20# hot idle, 70# around 4000.

How this effected pressure on the earlier motors with non timed tappets I don't know. Could be drilling in case passage to PRV on these early motors was different?? I don't know.

If the later timed tappets are installed the metering dowel should be removed & replaced with normal hollow dowel like the rear dowel.
Don

Thanks everyone for progress so far, including all vendors,especially British Cycle Supply, Jim at Jim's Motorsports for advice, and all who helped so far here at Britbike.com. First time using Threebond sealer. Easy to use and I expect it will work great.
Al