Pre-Unit Case "use or not"

1765 Views 15 Replies 8 Participants Last post by latte hardtail, Jan 1, 2012

latte hardtail

Discussion Starter · Dec 30, 2011

Well..., I had posted a few weeks ago about my purchase of a 1960 Pre-Unit and now after taking it down to nothing, find out the case has a couple pieces missing. An experienced semi-local guy to me said from the pictures it could be used, but if I'm already this far into it that maybe I should look for another case. There are no cracks that stem from the break or pieces to be found inside; so it must be from a previous rebuild.

I have attached photos for you comments, experience, and expertise.

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Tony the torch

· #2 · Dec 30, 2011

that piece that is missing really has very little to do with the operation of the engine. the tappet blocks are held in place by the barrels and does not need the case support there. the Triumph factory even eliminated the stitch bolts that used to be there on the T140's.
In my opinion you should be ok to put it back together and run it the way it is.

Tommo

· #3 · Dec 30, 2011

I wouldn't have a problem using them,I'd probably just check the surface is flat and true.

redasphalt3

· #4 · Dec 30, 2011

Run it!

whittiger650

· #5 · Dec 31, 2011

I might clean up those breaks but otherwise they are good to run as is. I would say preferably I would like to have the support of the rear of the hole for the tappet guide block but I wouldn't stress over it.

SixFingerJack

· #6 · Dec 31, 2011

I'd run it mate, grind off the sharp/rough bits and don't worry about it.
There's no great stress in that area.

harleyd4me

· #7 · Dec 31, 2011

Dig deep, you might be lucky and find missing chunk in the bottom some place and prep and TIG it back in. Could even mill something to fit ??

'59

· #8 · Dec 31, 2011 (Edited)

interesting comments, that's my job today to get those stitch bolts out.

i've been hammering the bejaysus out of one with an impct driver and my worry was i was i was going t inflict the same damage.

i've all but moolerd the screw head so it's last stop shop for me today using a bit of heat.

i may end up wishing i have a set of cases in the same condition as yours, anyhoos bsed on the comments of the knowing and knowledgeble above i'd say run 'em; all the best.

latte hardtail

Discussion Starter · #9 · Dec 31, 2011

Thanks for all the comments. I have more confidence in proceeding with what I have.

The guy I am dealing with locally has years and years of experience with Triumphs, and has the same sentiment. He also told me to look at the condition of the head as far as hairline cracks from the bolt holes inward towards the valves...... sure enough I found cracks. He said all of the 8 bolt heads end up developing cracks eventually; so I am in the process of gathering parts to change over to the 9 bolt later model cylinders and head.

On that note do the Pre-Unit rocker boxes mate up to later model heads at all?

whittiger650

· #10 · Dec 31, 2011

No, the rocker boxes will not bolt up to a Unit head 9 bolt or 10 bolt.

You probably don't need to use a 9 bolt top end either. You can sleeve the bolt holes on your Pre-Unit head or if they are just fine cracks as they usually are, run it like is.

Ace Classics in London, England has featured some articles in the past and seem to be in favor of sleeving those holes and I believe they make them too.

latte hardtail said:
He also told me to look at the condition of the head as far as hairline cracks from the bolt holes inward towards the valves...... sure enough I found cracks. He said all of the 8 bolt heads end up developing cracks eventually; so I am in the process of gathering parts to change over to the 9 bolt later model cylinders and head.

On that note do the Pre-Unit rocker boxes mate up to later model heads at all?

Tommo

· #11 · Dec 31, 2011

No,I don,t think it'll be as easy as that,think you'll need matching boxes and push rod tubes....have a look at this earlier thread.
I was lucky,I had a friend who gave me a full unit top end and crank for my pre unit engine.
http://www.jockeyjournal.com/forum/showthread.php?t=93415

The cracks go to the valve seats usually.

latte hardtail

Discussion Starter · #12 · Jan 1, 2012 (Edited)

Here is a '65 single carb head (9-bolt). It seems like my Pre-Unit rocker boxes match up. Will this work?

Will a certain year set of cylinders make it so I can use my push rods and tubes from my Pre-Unit?

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Tony the torch

· #13 · Jan 1, 2012 (Edited)

the reason the pre unit rocker boxes won't work is apparent in the last picture here..look down the head bolt hole and you'll see the head bolts were moved further out in an effort to cure the cracking that is common in pre unit heads and thus the head bolts won't go through the rocker boxes into the spread out head bolts of a 9 bolt head. it's really apparent when you compare the 8 and 9 bolt head gaskets.
there is easy a way to fix the pre unit head... if you order 4 of the head bolt sleeves from the head bolt holes next to the intake valves on a later 66-7? unit head, (they used these steel sleeves because the intake ports often went through into the head bolt holes), so then you drill out the pre unit head bolt holes and press in the sleeves it stops the air leaks form the cracks and you can keep on running the 8 bolt pre unit head even with the cracks in there.

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latte hardtail

Discussion Starter · #14 · Jan 1, 2012

Thanks for the insight Tony. I can not believe I didn't see what you saw right away. So in your experience by implementing the fix you suggest that the small cracks will not impose an issue down the road?

I just want to build something solid since I have it taken down this far.

Tony the torch

· #15 · Jan 1, 2012 (Edited)

that's the way my bike is and many others I've done before. I've got the exact right size drill bit at the shop I'll measure it for you later, all you do is freeze the sleeves and heat the head up put a little anti-seize on them and press them in, I made up a press tool on the lathe that keeps them straight, I've done about 6-8 heads and never had any problems.

latte hardtail

Discussion Starter · #16 · Jan 1, 2012

Good deal.

Still learning.

Thanks again.

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