"Kas" 29 Nov-02
hi group ; in the midst of rebuilding my 750 and would like to know
the permissable clearance of the piston lands and piston skirt to the
cylinder bore . i have .020 piston and rings .any info will be of
help. thanks Kas..

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Hello Ken,

Good to hear that you're making progress with your Inter.

Here are the specs you're looking for:

1) Clearance, bottom of skirt to bore: 0.08 mm (0.003" to 0.004" max)
2) Max wear, bottom of skirt to bore: 0.16 mm (0.006")
3) Ring gap in unworn cylinder: 0.015" to 0.020" max
4) Renew rings when ring gap exceeds 0.060"
5) Ring clearance in grooves (land clearance): 0.001 to 0.003" max
6) Nominal standard bore size: 71 mm 2.792" (add 0.020 for yours)

Clearance at the top lands will be hard to measure, and should be OK as long
as the pistons have been made correctly. If not, there's not much you can
do about it anyway ;-) .

Hope this helps.

.. gREgg

"Anders Lilja, Roger, gREgg, Bob. " 3 December 2002

I am going to blast the cylinder head fins since they have become grey,
ugly and dull. How should I protect them to become grey and dull again?

Will a high temperature resistant silver paint do?

Anders,

On my '67 Mk1a I cleaned the fins with brake clean and a bottle brush then masked and spray painted with silver high temp paint. After 5 years it still looks very good. I did this with the motor out of the bike, assembled, on a milk crate out in the driveway. 67REMk1a. dark red tank, in front of a white garage door. RickL 67 Mk1a 60 Meteor Minor 53 500 Bullet 5? trials bitsa project (needs a 350 crank, anyone?) www.ChiVinMoto.com Dear Anders, Bead blasting looks great as soon as it's done but it doesn't stay that way for long. When I lived in England, there was a process known as Vaqua-blasting whereby a soft aggregate was suspended in high pressure water, it had the effect of 'polishing' the surface as it blasted away the oxidised deposits and oil on the head / crankcase etc. If oil or dirt is present in normal running use, you can wipe it off with a clean rag and no stain is left. I did the crankcases on my 1949 RE Model 'G' with this commercial process and they still look good today. Since moving to America, I have not been able to find anyone with Vaqua-blasting equipment, in fact most people look at you in dis-belief when you ask about a source.That would be my re-finish of choice.

Roger.

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One of the auto body shops near where I live does blasting with baking
soda. It avoids the dimpling affect you can get on aluminum cylinder
heads from blasting with harder substances like bead blasting. It also
avoids the problem of having bits of bead or sand etc. stay lurking in
hidden corners and getting into the engine later. When I did my Triumph
cylinder head a couple of years ago, I persuaded a friend with a
blasting unit to try baking soda in it. It worked fine, cleaned the
head right up, but created a huge white mess in his back lane. Oh well,
it was just a non-toxic mess of baking soda. Washed away in the next
good rain.

Bob Cram

Blasting with baking soda is relatively gentle, and as Bob says, does not
present the hazard of leaving glass balls inside your engine. I've only
ever used it to remove oxidization from heat-treated brass stampings, and
found it pretty slow going, but I expect it should work pretty quickly on
alloy.

The system I used mixed teh soda with a mist of water, making teh process a
little less messy than blowing just the powder.

.. gREgg

"gREgg. " 8 December 2002

The trick is not to use more torque than specified, but rather, careful
assembly techniques.

First, with only 20 lb-ft torque on each fastener, you have a lot of
latitude for error. So, be sure you use a relatively small (3/8" drive)
torque wrench, in which 20 lb-ft is close to mid-scale or greater. That
will ensure greater accuracy ... I cringe when I see people using 1/2" drive
torque wrenches that read up to 150 lb-ft !

Next, ensure the threads in both teh studs and tube nuts are perfectly
clean, and check that they assemble with no drag. Wipe on a bit of oil from
a dampened rag onto the stud's threads to prevent subsequent rusting, but do not oil the threads since that may cause over-torquing.

Also, make very sure the studs are threaded tightly into the crankcases and fully bottomed in their threads. This is the most common cause of failed threads in the cases, something more common in the 700cc engines that had 5/16 BSF studs.

Turn your attention to the heads, and check the holes for the studs. Ream
them out with a sharp 25/64" (0.03906) drill bit; I'll bet you will find the top surface mushroomed over where the tub nut bears, so come in via the cylinder seating surface

... this happens when a previous person has not fitted the correct heavy washers to the studs. Look down into the holes
where the washers sit, and if teh seatings aren't perfectly flat, you will
need to correct that ... just about every head I've seen needs attention
from the tube nuts bedding down into the alloy because the washers have
been left out. I have a piloted counter bore I use in my milling machine to
correct the seating.

Something else I see messed up often is the seating surface for the push rod tunnel seal. This happens when the seal has come adrift during assembly, and is not correctly in its recess when the heads are torqued ... result is the seal beds a groove into the head, causing a nasty leak. In serve cases, it may keep the Cross Ring from seating, and subsequent loss of compression. I have a jig for my mill that I use for correcting push rod tunnel seal recesses that have been damaged that way.

Next have a look at the seating face of your tube nuts (also the nut by the
spark plug): their face need to be dead flat, so face them off in a lathe,
and just break the corner with a very fine file.

The "ASCII art" below attempts to illustrate the head nuts, as seen from teh
top, for the timing side cylinder:

A____B

_______C

D ___E

When you assemble, snug up (e.g., to 5 lb-ft) the nuts closest to the center of the engine (A then D), followed by the one near the spark plug (C).

Then do the outer most ones (B, then E). Be sure your push rods are seated correctly. Now your heads should be ready to torque. Torque them first to 15 lb-ft with the same sequence, let things sit, and recheck. If readings are stable, take it up to the full 20 lb-ft.

1. On the studs, you want just the slightest wipe of a film on the male threads to keep them from rusting in use. This film is not enough to alter the torque reading appreciably ... besides, you still have lots of drag caused by the face of the tube nut against the washer, and that will swamp out any reduction of friction caused by the wipe on the male threads.

2. Yes, checking for full torque the first time should be done by the traditional way of backing off slightly and re-torquing to max. After that,
when it comes to re-check after a period of use, I do it by the practiced application of teh torque wrench, without first backing off ... doing it that way gives a better feel whether you've 'lost' torque since the last time you checked.

If you've lost clamping pressure during break-in for some reason, it will cause more loss of torque than the small amount otherwise
eliberated by first backing off the fastener.

Let it sit for a while, and then re-check. If you keep losing torque, something is wrong, and needs checking because it will only get worse in use. Recheck the torque on all the nuts after you have installed the engine ... this is just to be safe: they should need no further torquing at this point. Leave the head steady off for now.

After having put 15 minutes of running time on the engine with the bike standing still (use a big cooling fan to keep the engine from overheating), kill the engine and let the bike cool fully. Re-torque the heads, and now assemble fully. If the torque readings are off more than a couple of pounds, you may have a problem. After you've put on about 100 miles, check the readings again. After a further 100 miles, the readings should table.

Hope this has been of help,
.. gREgg

There is a term, "blue-lining" (which might be called something in your country) which, as a wee young lad, I observed at Kockums Shipyard in Sweden in 1973 (appretince as I was). In the nex hall, I saw enourmous ship engine parts.

They were planned, by painting with very thin blue paint. Then lowering the flat surface down against a wide marble slab. Scuff it around a bit. Rise it, swing it around, and a grey haired old guy with a rare and admired skill, used a sharp instrument to "scrape" off filliments and making the entire half meter wide metal surface flatter (totally plane) to within an hundreth or less of a millimeter. Is something like this ever done on crank case halves.

Naturally we are talking about very small amounts of metal to be scuffed off here (or things won't fit), to make it seal even better.

Who would you expect to find that does it.(pref. in Australia) Which type of workshop. I have a bit of a mania about getting this thing completely oil leak proof.

What are your experiences with sealants. Hylomare? or is there any silicon based stuff one can trust these days?
Regards
Royal and Kickan

My personal choice for crankcase sealants is 'Yamabond' a silicon based sealant, grey in colour which blends well with the crankcase. Available from Yamaha dealers. For paper gaskets, I literally paint on a super thin coat of 'Wellseal' a British product, onto each side of the gasket face. I use a small kid's watercolour paintbrush, dipping it into the tube.
Wellseal also works well on crankcase halves (it never sets) but if there are any blemishes on the faces, Yamabond is a better filler/ sealer.
Roger.

Royal,
Just let me add my own experiances on this crankcase assembly business:
Firstly, scraping. A good engineering company should have the means to take say 10 or 20 thou from the surface of the case and leave you with a really flat surface, but surely this is only necessary if the surface is damaged. I did this some 20 years ago (!!) when I first bought the Series II as someone had levered the cases apart...
Alternatively if you want to do it yourself, use a sheet of plate glass. This is readily available anywhere, relatively cheap and perfectly flat. In the UK the stuff to use was known as Micrometer Blue though may have other names today.

Assembly. Easy, really; warm the drive-side case and enter shaft into race. Fit spacer, sprocket or whatever then tighten using sprocket nut to draw shaft through bearing. When tight, leave to cool down.

Mount on blocks horizontally, mating face up of course, and apply your preferred goo (I use Loctite) to the cold face. Warm timing side case, and gently drop over bearing. It may be worth using string on bearing to retain rollers; alternatively heavy grease on the rollers should help to keep them together.

As for sealants, Enfields used Wellseal which is still available, but there are better ones now. I use Hylomar on the heads and cross-rings; so far, with good results!
Important point;

After torquing headbolts (to 23lb/ft maximum), run the engine for approx. 500 miles / 700 kms gently then remove head steady and re-torque heads (reset tappets of course). If you don't do this you will suffer head leaks once you start to use large throttle openings!

Cheers,
Dave Hollyman

Yamabond #4 which I have found it here in Sweden from the local Yamaha seller. Quite expensive! But very good stuff I am told from several sources...

I have read a lots of warnings to use the silicone based sealant, "leftovers" get stuck in narrow places and engines have seized!

The thin blue colour used during "planing" the halves so the ar flatter in surface is called Machinist Dye in English. "Skavfarg" in Swedish you could get it from the nearest tool shop. An alternative is an ordinary marker pen, to detect where they touch.

Best regards Anders

Scraping mating surfaces to make them perfectly flat is a highly skilled craft, which if done poorly will result in disaster.

BTW, the 'bearings' that were intended to be scraped are quite a different variety than our modern Vandervell-type shell bearings ... which must never, ever be scraped. IN the old days (like Ford Model T days), crank bearings were poured into place using molten Babbitt, which then had to be scraped to get a proper clearance.

The other traditional use for scraping has been on lathe (and other machine tool) bed ways, to compensate for uneven wear from use.

Scrapers come in many sizes, and as George stated, can most easily be made from grinding smooth an old file. As for sources, the need to use scrapers has diminished greatly with the proliferation of precision machinery. I have ones made by both General and Eclipse, and I note from a quick search that at least http://www.csosborne.com/brscrape_1.htm is still marketing them. Note that if you can have only one, a triangular one to get, but they come in as many shapes as you can imagine.

There is little more satisfying than using a good quality scraper. Honed to razor sharpness, there is little you can't cut with one ... while a cheap one isn't worth blazes.

While Royal had mentioned use of a marble surface plate, I think you'd find marble far too soft for the task. There are many suppliers of good black granite surface plates which are quite accurate and very hard. They come mainly from Asia (go figure), and an 18 x 24" plate can be had for about $75 ... well worth the investment for many workshop tasks involving measurement. But, beware, it can get addictive, and you will soon find yourself owning a vast array of measuring tools to go with the surface plate ...

... gREgg