Hitchcocks Forum

Well, this ones been a long wait, I had the engine seizure way way back for those who recall and having had a less than brilliant time of things this past 8 months i've finally started getting the bullet in the process of 'back in one piece'........

Barrel has been honed, piston cleaned, new rings, sizes checked etc, it seems the clearance was tighter than typically recommended about 0.0025" - 0.0035" ish, having had a good ol google around it appears that 0.0060" is a far kinder clearance for the iron barrel classic, given the expansion properties of alloy vs iron, this makes sense.........

Sooooo With that cleaned and ready to re-assemble, I thought i'll just have a check of the main and scavenge pump delivery and ensure they're doing what they should be to rule that one out as a possible reason for the seizing. Using a piece of clear tube connected to the outlet thread and fed into the pushrod hole I worked the kickstarter and verified that oil was reaching the sump and being forced through the pipe, no quantity measurements of course but at least it's working, seeing there was a bit more oil in the sump than should be, I decided the quickest and easiest route to clear it was a syringe and tube, the tube I used first was far too short and I dropped the whole thing down the sump, I retrieved the syringe but not the tube, no problem, I thought, and went to look for my claw grabby flexi tool which i've had for years and used on numerous how do i get that occassions, nowhere to be found, so got another today, (almost a fiver now!), having drained the sump with a longer piece of tube i ferreted about in the sump and everywhere imaginable, I made a 'dislodging' rod from a coathanger and I spent ages trying to find the damn thing, I mean, seriously, where can a piece of clear plastic petrol line type tube 4" long hide in there?.................

Getting frustrated with visions of unecessarily having to split the cases and at the same time doubting my sanity that the tube was indeed in there and feeling like finding the nearest skip to hurl the lot in, I decided to drain all the oil via the drain bolts, front sump one, fine, oil tank one, has been hamfisted and overtightened at some point, lots of nice ally thread slivers coming out with it, a bit of thread left on there but now have to be very wary of overtightening!.......

I then kicked the bike over vigorously to see if I might dislodge said pipe, (bear in mind the engine hadn't rotated since the pipe was lost in there), eventually, it appeared bang in the middle of the crankcase and thankfully I was able to retrieve it.......

Now, I can get on with re-assembly!

Giving much consideration to getting it back together, running, MOT'd and then sell it, it's really trying me this one! The incredibly frustrating bit is, I know it's because it's been in the hands of a bodger and I'm slowly rectifying all the cobbled together half arsed stuff so by the time I sell it it'll be OK! We'll see how it runs after this and go from there.

Hello Matey !!--------- haven't heard from you for a while. Can see why now...Might I just query your clearance figures ?? Are you saying the honing was done "typically" at two and a half to three and a half thou ?? I ask because you don't often see clearances on these "cooking" engines quoted to four places of decimal..........Seems EXCEPTIONALLY accurate for what's needed....And did you mean oil tank rather than sump ??...........Anyway, glad to see you're UP & AT 'EM !!-------------We all do this last item I think ?? ------- Bags of time, money, effort, tears and tantrums to have a fully re-worked bike at the culmination of all our efforts.......................................then sell it ????? WHY ???? Keep it and enjoy the fruits of your labours old son !!------------- Ta-ra..

Hi Alan, good to see you're still patrolling, hope you're well..........

(I really wish there were an easy way to do line breaks on this forum)--------------------
What I meant with the bore to piston clearance was, when stripped and checked (and I emphasise) ROUGHLY as I don't have a dial bore gauge the bore to piston skirt clearance was about 0.003", from my googling and reading it seems that modern engine standards mean machine shops will typically allow between 0.0025" - 0.0035" clearance, which apparently is fine for modern hegh performance motors which are all alloy and liquid cooled etc-----------------
The consensus for the bullet however is that around 0.006 should be considered a realistic minimum, (this from build reports from people who race etc), due to the expansion differential between the iron barrel and alloy piston and that most of the seizures they've known have been running tighter clearances as this is what the machine shops typically work to and consider 0.006 far too sloppy, (the bullet manual states 0.007" as a max permissable)--------------------
After I gave the barrel a light skim with the hone and dressed the piston with some fine wet n'n dry i'm showing about 0.006" (again, this is roughly).-----------------------
Re the sump, I meant the sump, not the tank, the barrel is still off and the sump looked to have a fair wallop of oil in, (it turned out to be just over a cup but with the internal shape it was hard to tell till I drained it, I can only assume that the pipe had gotten itself well and truly wedged under one of the flywheels and spinning it finally dislodged it but I was beginning to despair and thinking was going to have to split the crankcases.------------------
Going to whip the timing cover off today and have a proper check of the pump spindle and such for extra peace of mind, half pondering if I should in case I find more horror bodgery in there! But while it's off I can swap out the oil filter for a fresh one and refill the filter chamber.--------------------- THEN I can start putting it together and think about firing it up for the first time in months.

Hi guys----------- Alas yes, I'm still "Haunting" these threads---------- OK, those figures of 0.006" clearance for our AIR-COOLED Bullet engines seem fine to me....In the main I would expect an air cooled engine to have approx twice the clearance of a liquid cooled one................. Regarding the timing case removal,}---- Take the quill shaft out first so's not to damage the cork or neoprene seal then remove the cover then, if you still have the old fashioned cork insert in the end of the spindle worm I recommend a change to the neoprene "bonded" type....Make sure you completely PRE-SOAK the filter before fitting.....keep the faith, brother !!!

.006" is a lot of clearance. More like racing space. .0035" is pretty standard as you say for a bullet motor (measured at the thrust faces) but what is required is a decent period of running in. I've heard all sorts of horrific suggestions such as starting the motor without oil and reviving it flat out to do a quick bedding in and these may work for racing motors from which you only want a short and furious life. However, 1000 gentle miles at no more than 50mph and no heavy loading with at least one oil change early in the piece is in my experience the recipe for a long life motor.

I'm still going to go with what I have and see how it goes, if i get a bit of piston slap, I can live with it but I know i'm under the 'wear limit' specified anyway, I think also that if 0.0035" is standard on bullets, then surely 0.007" wouldn't be the wear limit, it would be considerably lower, 0.0045" maybe.----
If need be, I have another 2 piston oversizes to go up before having to resort to a new barrel and piston.----
I've never heard of running an engine without oil to bed in the piston rings, that in itself would completely defeat the purpose of honing, which to to help retain small quantities of oil to assist the rings in wearing into the bore, a recipe for disaster without doubt.----
An oil change about 100 miles in is on the cards after the rings have bedded in a little, i'm a firm believer in frequent changes anyway, especially in air cooled engines.----
On another note, I removed the timing case cover and was delighted to find all is well in there, the scavenge pump face could do with lapping in a little as it's mating surface isn't perfect so i'll do that then give the whole assembly a thorough clean, blow through with compressed air and re-lube and re-assembly, i'm just waiting on a timing cover gasket, ordered last night as the one i thought I had, I didn't have!, ( I thought I had a full gasket set in the shed, turns out it was a decoke set)----
New filter is ready for fitment, (old one wasn't too bad as it goes), the cork in the worm gear was just fitted after the seizure as the rubber 'cork' insert had started to perish and split, so being good for now and intending to remove the timing cover for future changes making replacement of the cork, (and filter), a doddle, i'll stick with that for the moment and look at the bonded one after i've got back up and running and am happy with it.----
Now to clean off the gasket surface and clean out the cover so i can re-assemble the oil pump drive.

Hi guys------- I have to say that I'm still chuckling over these sizes that include a 1/2 thou (ie a 1/4 thou cut,) on an old Enfield engine..................Assuming that we are using the Std. 6:1 OEM piston, with it's tendency to seize and/or decapitate itself, and run it in an iron barrel--- a "hot" situation--- then even a split-skirt piston will function better with more than three ( and a half ) thou clearance..............For those not of an Engineering experience have a look on an older 6" ruler that has 1/100's etched on it.... You'll notice that the thickness of an etched black line is approx. the same as the gaps in between... ie the line is approx 1/100" OR 10 thou. !!..... And 3.5 thou is approx 1/3 of THAT thickness........... My Classic 500 has our hosts ACCRALITE 8.5 : 1 CR piston fitted so I've just had a look at its' enclosed instructions which, amongst other things, gave the piston to bore clearance (at 20 deg. C) as}--- 0.0055" to 0.0059" with a honed "Plateau" finish at 25-30 microinch CLA...............and it runs in an Alloy barrel...When starting from cold yes, there is a degree of piston slap BUT, when up to running temperature it is as smooth as silk and NO signs of "nipping-up"...However, I DO AGREE ( hey !! I'm not ALL Mr Nasty, you know !!) with SIMON'S running-in advice... That's almost a direct quote from any riders handbook of the time, and is VERY appropriate to these Redditch-derived rascals that we covet !!!!------------------ So "Come-on" Mk1s, slap some oil on that "6 thou." piston---pop it in the engine and have a nice ride-out tomorrow in the SUN !!!!, it'll be alright matey !!

I would like to know how you could come up with a figure of 3 thou without a bore gauge, my eyes can't see 3 thou

As per my first reply / third post on this thread.----
Measured skirt to barrel clearance at thrust faces (and I do emphasize roughly), with feeler gauge, I wouldn't be able to 'guesstimate' 0.003"----
No, it's not dial bore gauge exact, but it's near enough for me right now.

Still waiting on timing cover gasket Alan, ready to rebuild soon as I get that. Need to recheck timing as I disturbed the distributor gear while checking/cleaning the idler gears, I know I'm only one tooth out if I'm out but will need to be running to check dynamically as it's running electronic ignition, should be near enough to start as the magnet is bang on with the sensor at tdc static just now.