classic motorcycle forum

Liking your work so far. My preference is for the Hylomar blue as have seen too much RTV stuck in oil galleries.

Yes, that's one of my concerns, not that there's many oil galleries in this thing!

Quote from: Rockburner on April 01, 2026, 11:04:30 AM

More grinding...

I think I'm getting a little pressured and starting to make stupid mistakes - so need to try to slow down a bit and be thorough.

Yes. What you're doing is not OK; I'm not sure why. Better get some help.

Leon

Care to be a tad more specific?  I did in fact forget the output bearing liner so I know I made that mistake - but have I made any more? This is still my first time doing this sort of work, and part of the reason for describing every step is to make sure that I'm not missing things, even if I have to go backwards again.

So, last night I started out by making up the new base gasket :


I have made myself a set of templates out of some thicker carboard and used that.  I've trimmed the inner circle to be slightly larger, so hopefully there won't be a capillary path from the cylinder base straight out under the gasket this time.

I also made up a quick Mag-pinion cover gasket from the excess paper to avoid wasting it.


I then tidied all that away and got down to the main job of the evening.  I finished stripping down the crankcases again and experimented a bit with the shims just to confirm the crank-touching-the-cases issue.

I'm sure I took more photos over the course of the evening, but it looks like the phone camera didn't actually save them, which is odd....

Anyway: here's a few shots of the same modification that was done to the Output side of the assembly at some time before:



This is, essentially, what I need to emulate on the other side.
Interestingly.... the output side is the nut that was removed when we replaced the big-end bearings: in this photo you can see that the nut has been done up slightly tighter this time than it had been before: you can just see the threads on the crank-pin becuase the nut has been rotated on the pin about 5 degrees more this time.


I decided that the grinding would have to be done.
So I cleaned up the wheels as best I could, wrapped a tea-towel around the bigend to prevent too much grit getting to it:


Protected the timing-shaft oilway:


Experimenting with the best way to clamp up the wheels so they don't wander about.


Then remembered I have a little B&Q trestle that would make life a bit easier, clamped it to that and did some taping to protect other gaps and holes:


I also marked up the approximate area that needed work:


In addition I wrapped some duct tape around the shaft just in case the grinder got away from me!

Work in progress:






I did the majority of the grinding outside (to avoid any conflagrations...!) with a 115mm Ryobi, and it worked very well - nice and controllable.  The light was just enough that I could see what I was doing, but more would have been preferable.




And for some reason, that's where I stopped taking photos. (soz!)

I got to a point where all the marker had been eradicated, then, as the light was fading, I took the trestle back into the workshop and get the Dremel out to tidy up and polish.  I used the Dremel grinding wheel to make the ground-away area slightly concave and to take off the rough edges, then wire-brushed and polished it a bit.

I then cleaned it all up, using meths and paper to try to get rid of as much grit as possible, before removing all the protective stuff and unclamping the wheels.

I tried the wheel in the cases with a 0.023 shim (which is the minimal it would need I think.. I stil need to figure out exactly the best shims to use - more on that later*.

The $%^&&er is still scraping. GAH!

So - I need to take a bit more off - I suspect I just need to "round-off" the ground area so that it clears the head of the bearing-line-fixing-screw.

It's sooooo close!! 


* Something from the conversation I had with the Guru:  Although the recommended end-float in the Greenway book (which is the Speedway "Bible") is 0.012" - 0.015" : The Guru recommends letting it be a little looser : 0.015"-0.020"... and the engine will rev more freely.  Given that my engine is "square" (bore = stroke) and will be wanting to rev more easily due to that: I am taking that advice and giving it strong consideration.  The flip-side is that the Guru tends to be building up engines for actual racing... ie, they'll get stripped down again after a season, and a season is not really that many miles.   So: my thinking is to compromise on this and aim for an end float that takes into account the hopefully longer mileage that the engine will do before it's next strip down:  I'm going to aim for around 0.015", or slightly higher, end float: ie the looser end of the Greenway figures, and the tighter end of the Guru's advice.  The aim is to have the engine in good fettle for a few years of riding around on the road with the occasional classic "parade" track-day.  It's unlikely to get utterly thrashed, but I would rather not be rebuilding it every winter!

"I fitted the 0.060 thrust washers on the timing side, and a 0.023 on the output side..."

I guess this is part of the mis-matched engine thing. It would be nice if there were no shims between the face of the crank and the bearing inner. Usually this is accomplished by shimming the bearing outer in the crankcase. As it stands, your shims are pretty large and heavy, and there could be quite a "hula hoop" effect as they spin around the main shafts (or the shafts spin inside them), which could cause damage to the shafts and/or the shims. In reality, if you're not going racing, it will probably be ok. But it would worry me. Maybe check with your JAP man?

You mention there is not much end thrust when the engine is vertical: true provided the piston is square and centred. You might be amazed to see the inside of an engine that has been running with a bent con rod!

Leon

I took a 0.050 and a 0.040 thrust washers out of the engine when I stripped it, and the internals seemed ok. The engine is pretty unstressed and won't be used for racing or anything.

The thrust washers are part of the design on the engine, it's not possible to adjust the main bearing liners, they're pressed into the cases, and the thrust washers/shims allow for the end first to be adjusted. This IS a 1930's design....

But you're right that a call to the expert is in order.

Oh dear.

Re gasket sealant, I've used Loctite Aviation Gasket Sealanf No. 3 https://autopro.com.au/ap/Autopro-Category/Brands/Loctite/Loctite-Gasket-Sealant-No-3-Aviation-50mL---3JA/p/DI01199 for may years. It's a bit old fashioned, but is has many properties that I like. It doesn't set (surely it's best feature - I hate nothing more than to find bits of sealant crap floating around in an engine), it seals well, it's cheap, and it's a dark-blackish-brown colour. Just a thin layer on any gasket, or machined metal-to-metal faces, wipe excess off with a rag - looks good and works well.

Avoiding things clanking is the ancient art of "fitting". Lots of measurement and care required. Often forgotten is that things expand when they get hot, so clank-free  on the bench is not enough - correct clearance is important. Make sure the rod is central to the crankcase opening, and double check that the piston is precisely at 90 degrees to the cylinder base. (You can do the latter with an engineer's square on the crankcase mouth, remembering that the piston is not round, and probably tapered! If you do a trial fit of the cylinder with no rings, the gap between the piston and the cylinder should be even.)

All good fun!

Leon

I'll have a look at that gasket stuff - The 3Bond seems to have separated in storage, I think that's why it's so runny and not working well.  I'l have to try to re-vitalise it a bit!

Yep - the heat expansion needs to be born in mind etc.  All good points!

Soooo, I hopped and skipped into the workshop on Friday afternoon, full of the joys of spring!

First thing I did was remove the larger half of the head-steady so the bracket that goes onto the head would be easier to fit...
My Dad's choices here are clear... this nut is NOt coming undone!


Then I undid the Rocker  box again so I could document the assembly process properly (as promised).
First: Assemble the rocker arms and bearings into the bottom half of the box like so: Note the "outboard" bearing liners have been pushed "down" out of the box body, so the rocker arms have next to no end-float:


Gently put the top on.


This is what the push-rod side of the box should look like - the rocker-arm bearing liners will be proud of the box face:




Fit and tighten down the "inboard" fixing screws, This will lock the "inboard" rocker-arm-bearing-liners in place, but allow the "outboard" bearing liners to still move: when the cover is fitted on, it won't meet the box edge, because the stubs on the inside face of the cover are meeting the outer end of the rocker arms: 


You can see the gap all around where the cover meets the box.


Tighten up the cover.  This pushes the rocker arm against the bearing liner, and pushes the bearing liner into the rocker box.


Most of these engines have a single-sided wing-nut/bolt for the rocker cover, but I just have a plain set-screw (bolt)


The bearing liners have now been pushed into the box, and the end-float of the rocker arms is limited by the stubs on the inside of rocker cover face.


Note - this bearing liner (exhaust side) is still a little proud.


Now fit and tighten the "outboard" fixing screws to lock the outboard bearing liners into position.


The assembled rocker box: the rocker arms should "flop" about freely, but without rattling around.  With that in mind, it's worth remembering that they only need a small-ish amount of movement  in actual usage.


Fitting the Rocker box to the Head:
The lower valve covers go on first, then the Rocker box:


The Washers on top of the Rocker box are spacers to allow the head-steady bracket to fit easily.


Head steady bracket:


Rocker box fitting bolts - getting these aligned is a bit of a git:


Test fitting the upper half of the valve covers:


Ah - yeah... the oil feed banjo fitting - that would have been easier to fit EARLIER....
I may need to find another one of these, it's brass, and the hex "head" is knackered.


And as for these little gits....


These are the oil feed into the valve-guides, and they are a pain in the arse to fit, so I took the Rocker box off again to fit them!


They're just  a push fit into small holes in the head, so sealing them wo'nt happen. :roll:

At this point I was pondering something and happened to be rolling the crank back and forth....

when I heard and felt a distinct "clunk" coming from the movement of the crank. :wtf:

Video:
https://youtu.be/_VnexesDQKA?si=NvSMuXI4gSz3eD10

So... I started stripping everything down again! GAH!

A rather unpleasant discovery  when I took the barrel off was this oil weep under the base gasket:




To be honest, I'd had a nasty suspicion that I'd seen dirty oil at the bottom edge of the barrel, looks like I was right.   I think the 3Bond had soaked into the gasket, or maybe it just wasn't thick enough??  Don't know: but when I fit the new base gasket (I'm going to make another one because this one is very tight around the barrel base), I think I'll use Blue Hylomar instead of 3Bond, maybe, don't know, we'll see.  I'm not impressed because this was weeping with zero provocation whatsoever, there's not even any crankcase pressure at the moment - the timing side is still completely open so this was weeping simply through capillary action.  It is interesting though that the weep lined up with edge of the barrel base that is broken (see earlier photos).  I think pulling the gasket away from the barrel base may help, hopefully!

This time I took the barrel studs off before the piston - makes it easier to get to the gudgeon pin circlips.


Another shitty video...
https://youtu.be/mW1prhFqC4U?si=zz84myipwydojLNr

(Apoloies about the portrait videos, I set things up in a hurry, will do better next time!)


So - the cases were split again!



I did figure it out though...
THIS:


is scraping on THAT:


I think the big-end-shaft nut is hitting the main bearing liner locating screw:


really not sure how the design would even allow for that.. but, it appears to be what's happening. I can only assume that previously, the thrust washer on this side was thick enough to create a clearance: IIRC the two thrust washers fitted were a 0.040 and a 0.050: because I've fitted a new liner on the output side the clearance in the cases is (I think) now a tad smaller, so when I did the crank end-float I ended up with slightly thinner overall thrust washers fitted.

I played around with the thrust washers: simply moving the fitted ones around (ie, moving one from the output side to the timing side), and this did seem to create enough clearance:

Video:
https://youtu.be/iPZ7o_STyd0?si=gztkDB_r870HtbDh

But, I think I'm going to do some more checks before I start the assembly process again: I'm going to make sure that screw is down as far as it will go, and I will likely do a touch of grinding to take some metal off the top of the screw head, just to increase the clearance a bit more.
Then, I'll fit a thicker thrust washer on that side, and re-do the end-play by fitting the correct thickness thrust washers on the output side.


Funnily enough... the output side of the bid-end shaft has the nut and shaft ground away slightly in a fashion that would indicate that this issue has happened on the other side.  While pondering this over the weekend (I've thought of nothing else), I did wonder if maybe the fly-wheels got swapped over when we replaced the big end bearings, but I'd be very surprised if this was the case, the crank wasn't completely disassembled: the output and timing shafts were not removed from the wheels, (and it's not a reversable assembly), so I am slightly confused.


Output side crankcase cleaned up nicely:


This stuff rocks!



So - all this weekend I've been pondering my options.

I think I'll start, as mentioned, by trying to take some material off that locating screw (won't be much, just enough to make it less of a prominence),
cleaning up the rest of the sealant from the cases,
Re-doing the crank end play with a thicker thrust washer on the timing side to ensure clearance,
Make a new base gasket (maybe with a thicker bit of paper... not sure really)
Then restart assembly.

few steps forwards.... several steps backwards.... hey ho...  it's all a learning experience!

Looking good. I notice there's not too many fins on that cylinder head. Was your dad running it on petrol?

Leon

Yes, the flywheels are 350, so the piston travel is only 80mm, compression is down to about 9:1 (ish), it was put together as a road bike, not a full blood race engine deliberately to make it easy to ride and to use petrol.

Nice going.
Probably an optical illusion, but is that piston circlip fully seated in it's groove all round?
I've been caught out before where the supplier fitted round section circlips in a square section piston groove, and they didn't seat well.

It is yes, i had to look 3 times though...