Big Inch Shovel - Build Thread


Club Member
I think Alex at fast lane may have the formula for the calculation for the dome as he uses it in his head working and may be able to give some valuable input as to redoing pistons and heads ect to keep compression in a sensible range for pump gas (especially in some parts of Europe when travelling) and giving the starter an easier time (y)

the formula for the dome is given above, you can re-arrange the equation to get parameters required.
or much easier go here and use the online-calculator, as i used. (y)

Screen Shot 2023-11-19 at 13.36.55.png

alot of this build will beased on my experiences building my 98" shovel. just larger capacity.
starter-relief is being taken care with compression-release, as on my 98".
mechanical-cr on the 98 about 9.7:1, cc'd. i'm upping it a little on this due to a slightly longer cam to help fill the bore bleeding a little off.
plus it'll hopefully have better combustion; squish, higher VE, less full-advance and less likely to knock etc.
this is all conjecture, somewhat theoretical of course, but methods are tried and tested, i'll just try and implement as much of it, as close as i can (y).


Club Member
so with the piston-copy in the bore.
i measure out 100g of water, dyed with blue food colouring.
the scales compensate for the measuring-cylinder, which weight 40g


i then fill the cylinder-void. i use a piece of perspex with holes to help expel air to get it completely full.
you can do it without the prespex, get the cylinder level and fill it right to the top. you do get a little extra, maybe a cc or two due to water-tension.
thats why it's best with the lid.

i first bulk fill it, find it easier than filling through the lid. i don't have a burette so use a combination of 100ml syringe and 5ml syrings. it's bit of a phaff, hence the bulk fill first.

bulk fill

capped off, lid is smeared with grease at edge to seal and stop it floating up?

remaining fluid 28g = 28cc volume.

just for curiosity i filled the valve reliefs with plasticine and cc'd the lump inside the 5ml syringe to measure the displacement.
it worked out at 1.2cc. they look like they'd be more, but it is what is is.


so this concludes the piston dome.
measuring the dome it has a height of 10.94-10.97mm, lets split the difference 10.955mm
a diamter of 83mm
the radius that gives this 'cap' is 84.08mm.

theoretically that gives a volume of 30.325cc, remove 1.2cc for the valve reliefs, giving 29.125cc.
so we're about a 1cc out. thats close enough at this stage.
the machining will be precise in comparison to my compass-drawn arcs and hand-crafted dome.
i suspect it'll bebetter than this on the actual piston, but a 1cc deviation is negligable to c:r at what i'm dealing with.

more important is that both pistons are the same value rather than the specific value itself.


Club Member
right, i'm coming close to the end of what i've done so far on this build. this has all been in retrospect.

so, not that i have found my dome dimensions i need to makre sure there is enough material left in that piston once it has been machined.
i tried taking internal measurements and external measurements but it wasn't working out. i obtain a photo of another JE 3 13/16 piston, but for an evo that had been cut in half. the piston-die looked identical underneath. i hoped it was the same piston, just without the dome, but it wasn't subtle differences rendered it unusable. contacting JE for a possibel cross-section drawing was met with no response.

so i modified the mould enabling me to take a full copy. the previous copies were 'solid' slugs. i needed the internal structure too.
i basically placed the original piston back into the main mould.
cut some circular and square recesses to act as locators.
built a wall around to contain the silicon.
and filled it up.
result was an additional half-mould that has the internal structure.

copy came out excellent. detail is amazing. even the numbering etched into the ally come out.

so now that i have full piston copies, i can slice them and measure material thickness.
i re-shaped a piston as close to possible the final model. it ended up slightly smaller, butthats ok. i know my actual material is more.
plus it's only significant at the very top of the dome. as it falls off the deviation in size becomes negligible.

obviously reshaped piston the lhs and original on the rhs
the thinnest area of the piston are effectively the same being untouched in the reshaping process.
these are the valve-reliefs, as expected.
the red-line on the rhs piston shows the arc the re-shaped piston follows.
you can see the largest impact is pretty much central only, once you get into some serious material.
discussion with builders/racers that know alot more than me, to say the least regard what i have as plenty of material.
0.3" is considered safe for moderate fuels and compression.


now a piston dome/crown isn't just there for structural integrity and compression.
it's mass is important to transfer heat for cooling. i think conversations about that will be just too 'academic' for my concern.
but, the pistons once machined will be getting coatings. certainly lubricatingn ones on the skirt, not sure about thermal ones for the top.

i think i'm good here.


Club Member
OK, this is the last update.
got an email from Paul, my machinist.
i ask him to photo the process fo all he does for me, so i have a record for my build logs.
he has completed the cylinder heads regarding cylinder fit and plugging up the oil-dran.
they will get more work later, requiring machining for external oil-drains and possible valve-seat/pocket work depending on what cam i opt for.
these ultima heads should handle 0.6" lift, well see when i measure it.
but some cams are in excess of that.

welded up the oil-passage

check trueness for skim.

check concenticity for bore

machining done

test fit

so thats it, everything done up to date.
i'll pick these heads up next week and get a mock-assembly going to start checking clearances, limits etc.
i'll take the piston-copies, so Paul can start experiemnting with machining those to required dome.
it's all starting to come together!


Club Member
Hi Julian, what's the advantage of external oil drains over the standard internal and will you feed the oil back into the bottom of the cylinders to lubricate the piston skirts?

Thanks again for taking the trouble to post all this.


Club Member
Hi Julian, what's the advantage of external oil drains over the standard internal and will you feed the oil back into the bottom of the cylinders to lubricate the piston skirts?

Thanks again for taking the trouble to post all this.
Ron, traditionally external drains were used to remove the potential 'weakness' of having the draining-oil passing through gaskets. Also oil is apparently 'cooler' as it hasn't past through the cylinders. commonly returned into the engine case around the timing hole or through the timing-hole itself for simplicity. some prefer elsewhere; tappet-blocks, case-primary-return etc as to limit the amount of oil-drag on the flywheels. but this all gets somewhat 'academic' and meaningless in a street-engine i.m.o.

personally i'm not keen on them, it can easily make a motor look untidy or 'clutterred'?
likely completely unneccessary on a 'street' engine? possibly if you are super hi compression, racing, blah blah.

in my case with this build, i have no choice. due to the larger bore, the cylinders don't have the provision for draining oil through the cylinders. i'll be looking to return the oil into the engine case, likely either side of the timing hole and plummed in as neat as i can. but will conclude that lot come the time.

John, regarding the quin, possibly, condensed version, main aspects etc. we'll see.


Club Member
Thanks Julian, I did find on my Pan/Shovel the first time I took a head off that the oil drain hole in the head gasket was much smaller than the holes in the barrel and head.


Club Member
thats a fine looking motor. (y)
i think once you get to crap all over the place, more IS more.
i look at the above engine and don't think in any instance it looks cluterred or untidy?

hoses can look a mess, they're sort of uncontrollable compared to hard lines, but have the advantage of way more flexibility/repairability out on the road. but, i've never seen hoses with 'banjos' fitted to the ends, that looks neat, more 'in-keeping' than say AN-fittings.

for me, its to do with visual balance and symmetry, i'm a little obsessed with it.
whatever ends up with my external drains they'll need to be a mirror image.


Club Member
Just thinking aloud here but if your oil drains went in either side of the timing hole wouldn't there be a lot of pressure blowing oil back up them. A friend had the timing plug blow out taking part of the thread with it. On inspection it was already damaged but it's still a fair bit of pressure.


Club Member
Ron, no, if you think about it, it's not that dissimiliar to venting through the cylinders, it's still kinda sucked out/down by case vacuum.
you just need to makes sure the bore of the pipe/drain is sufficient.

i suspect your friends engine was sufferring leakage past rings or maybe other venting issues creating excessive c-case pressure?
there shouldn't actually be that much pressure generated within the case, several psi maybe?
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Club Member
Impressive work, not just in the engineering, but the time taken to photograph and describe the work. I've worked briefly with resins and silicons in a sculpture casting workshop and know some of the pitfalls in moulding and casting. Great stuff, thanks for posting.

I think my shovel will be staying stock!


Club Member
I have made a little progress on this.
i got the heads and remaining cylinder back from paul, the machinist i use.
first job is the initial mock-assembly of the rotating mass to see if there are any issues and take it from there.

first job is to assemble 'half' a crankshaft with conrods into one-half engine case.
This enables me to examine clearances of rods, pistons, flywheels, spinning clatch to makesure it has enough room.

mmmm, first thing i notice is that the crank-pin thrust washer is sitting proud in the pinion-side flywheel. Some of these parts, this is the first time I have actually seen/inspected them properly. Just goes to show, you have to check everything, no-one is infallible, not even reputable suppliers of quality parts.

if i'd have bought an assembled crankshaft, that could have been like that and gone unoticed.
waiting to possibly come out and cause whatever catastophe down the road.
take nothing for granted, check everything, trust on-one.


likely, this has been caused when securing the washer with the dot-punches, lifting one side.
it's poor workmanship really, even if it happened, it should have been corrected before going out the door?
maybe it dislodged during transit? but that just demonstrates insufficent security in the part, also poor workmanship?
anyway, i use my sprocket shaft bearing tool to clamp either side of the flywheel to press the washer down into it's counterbore properly

sprocket shaft bearing tool. normally used to check tapered-bearing endplay.

I only use the M12 bolt and two heavy-discs plus additional large washers to distribute load better and press it back in.
didn't take much.


after checking it's all good around perimeter,
i add another x4 further punches to add integrity to the security of the washer.


happy with that, i move into the pinion-shaft.


Club Member
i fit the pinion-shaft hand tight only to make sure the taper is seated.
now, with this build i was investigating the use of a late-evo pinion bearing.
my thoughts are that a longer-roller bearing will be better than the shorter rollers as used in shovels.
i have previously sized the rollers and concluded what i neede to do to obtain the necessry clearance.
but i was concerned about the overall 'length' of the bearing, it looked like it would be too long when i was measuring rollers.
not i can investigate properly.

TnO flywheels are machined as early to mid 80s flywheels and have a small shoulder machined into the pinion side to accept a thrustwasher.
shovels typically have a 0.070" thrust washer either side of teh bearing cages, but evo bearings are used without thrustwashers.
you have to simply determine what will work, if it infact will?

the pinion-shaft mounted into the flywheel sits proud of the shoulder, it doesn't sit flush.
the amount it's proud i guess is determined by the machining of the tapers?
nothing concerning, just somehitng inevtible whem matching parts from different manufacturers?


so, if i place the evo bearing simply over the shaft, the rollers will overhang the pinion race, somehting i do not want.
i must place the bearing so the rollers are centralised as best as possible on the pinion-race.

here you can see the rollers would sit low and overhang at the base of the pinion-shaft.
not ideal.

if i place a 0.070" thrust washer under the bearing, it centralise it nicely on the pinion race.

but the problem with doing this, is that it doesn't leave enough clearance to get the retaining-clip in the groove.
the retaining-clip used with evo-bearings has a wider O.D than sovel clips to retain the bearing.
shovel clips can't be used, unless a thrust-washer is used to retian the bearing.


it looks like the evo-bearing can't be used in this build, which is a shame as i wanted to give ot a go.
on a different combination of pinion-flywheel-taper, the shaft might sit higher and allow it to be used.

i worked out that i'd need a maximum of 0.040 to 0.045" thrust washer under the bearing to allow the retaining-clip to be used.
this would place the rollers dangerously close to the edge of the race i.m.o, not something i want to do.
i know guys that have done this, numerous times, so it is possible, just not in this case?

come the time i will simply fit shovel cages and rollers, we all know they work,
i just wanted to expand my knowledge and try somehting different. you can still get OEM evo bearings and i'd rather use those in a bottom end rather than the potential poor quality third party parts. especially in somehting as importatnt as this.

i have some NOS OEM cages and rollers that i sourced for this build, as a backup incase this evo lark didn't work out.

so anyway, canned the evo gubbins and fitted shovel rollers for the mock assembly.
fitted the conrods, pistons with top-ring fitted and slipped over the cylinders.
i now have an assembly i can check clearances.

rotating assembly fitted in case-half to expose workings.
under the pistons are 'delrin' plates i made to slip over the base studs and stop the rods clashing against the case-wall and pistons aganst case-tops.


Club Member
assembly with cylinders slipped over.
i don't like the gaudy axtell badges on the cylinders.
i'm going to remove them and either leave them off or get some 'old style' badges made up?

so onto clearances.
when i rotate the crankshaft, the pistons just 'kiss' the flywheels.
it can still rotate, but they do touch.

here you see the front piston touching the flywheel at the period of BDC

same with the rear piston.

these pistons are stated to work with a 5" stroke, but they clearly don't, or not without issued down the road anyway?
again, check, check and check.
no biggy, i'll simply file the pistons in the area to clear.

going through piston-to-piston clearances at bottom-centre they look fine.
i'll measure them for my logbook, but eyeballing there is plenty of room.
the obligatory clearance is 0.060", about 1.5mm and after a while you know by eye if you are easily under or over this.

you'd get a 'bagger' through there?


Club Member
OK, onto those fouling pistons.

first i take everything apart.
there's gonna be a lot of assembly, disassembly, assembly, repeat on this build.
it's the way it goes. you spend hours and hours and hours of fitting, checking, adjusting etc untill all is good.
and then spend a trelatively short amount of time putting it all together.
it's no work at all to put a shovel motor together, it's all the work beforehand to make sure it goes together right and stays together.

so, i scribe the pistons with a 0.060" line from the edge in the area they are fouling.
i then scribe a perpendicular line at the point the pistons touch. flywheel has conveniently left a 'kiss' mark at the spot.
i then scribe a line from that tapering off to the edge of teh skirt to where there is enough clearance.
i'm left with a small 'triangle' that needs removing.

on the left is the piston scribed up.
on the right, masked off to identify the area needingn removing more easily, and protect the immediate area.

so here, on the left is pistom marked up, ready for filing.
on the right, filed.

here finished skirts, should be ok now.
but i have to assemble it all again and check.
i left it at that for today. out of degreaser and i need to clean the pistons properly to get all the filings out.

rest of it seems pretty good. as intended.
with no base gasket i have effectively zero piston-deck. this was intended and specified with cylinder length at manufacture.
this is so my base gasket will dictate my squish-band.
i have 0.032" copper base-gaskets, so that will give i.r.o 32 thou squish.
my experienced has shown me copper gaskets crush very little, if at all.

also, my fire-ring is 0.225", again specified at manufacture.
typically cylinders have a 0.200" fire-ring and subsequently the same counterbore in cylinders.
so when you fit a typical 0.032" gasket, possibly crushed to 0.020" if it's one of those blue cometyics or msl ones,
you get this gap above your fire-ring.
to optimise quench and combustion i want to close everyhitng up as much as possible.
so, that 0.225" spigot, in the 0.200" counterbore of the heads leaves a measured 0.024" gap between gasket-faces.
i have 0.026" copper gasket to fit here, effectively closing that gap down to 0.002"

effectively zero piston compression height at TDC, as intended.

mock up with the ultima heads.
starting to look strong.


Club Member
Wow! And here's me struggling to cut a bolt off square, yes I do dress it up with a file after.


Club Member
Ron, if you can cut a bolt off, square or not. you can file pistons or whatever else come to that.
it may seem daunting to take a file to some brand new quite expensive pistons, but it's just metal?
take your time, think it through and don't balls it up is my approach?

Anyway, i did some more today, i had to fettle the pistons as clearance was quite enough. also did some preliminary checks with the ultima heads. i'll post that lot up later. i digress a little, had a delivery today.

for years i've been using a small chinese bench drill that was given to me. it has served me very well over the years for all sorts of drilling shenanigans. but i always was going to replace wit with somehting more substantial, have been looking at older british bech drills; foboco, startrite mercury, stuff like that. a descent one can cost a fair amount, many hundreds of pounds.

my small chinese drill.


After lots of reserach, thoughts on it all, i've taken delivery of this...


It's an Alping RF-25, effectively a re-badged taiwan/korean 'RongFu/Naerok' bech drill/mill.
A brummy base company grahem engineering imported them from the 70s, as did many others.
now, i'me very aware of these machines, there limitations, capabilities and disadvantages. Bridgeport it ain't.
But for a home workshop, small-footprint, they are a very capable machine. major big stuff, highest precision can always be farmed out.
These 70s-80s machines are better made than the equivalents of today. it weighs 200kg.
This one, a relatively little used machine from a reputable source hopefully serves me very well. just gotta learn to use it.
Now looking to make space in my workshop for a Boxford lathe in the near future. I should be sorted then for all bu the major stuff?