phylo_roadking

I'm putting this here, although it's as mch about artillery as it is about tanks! I'm chasing down information on the Close Support tanks in the british Army in WW2 - the couple of howitzer-armed tanks attached to squadron HQs to provide smoke and an occasional HE round for self-protection... Up until certain later marks of the Churchill, and the Cromwell - various British tank types were occasionaly fitted with a low-velocity QF 3in howitzer in place of their 2-pdr tank guns. Up until the middle of the war, these were primarily (supposed to be!) used for throwing smoke for the squadron they were attached to to manouver in...and their "ammo" load-outs reflected this, several dozen smoke rounds vs. a couple of H.E. rounds for self-protection if an antitank gun came a'knocking! Now - in 1939-1940 a low velocity 3in howitzer replaced the old Vickers 3.7in howitzer that had been used in some Vickers' designed tank types until then, specifically the just-prewar Cruiser A9s and A10s...and the Matilda MkII C.S., Tetrarch C.S., Churchill MkI and II C.S. Crusader C.S. and Covenanter C.S. all mounted the new 3in weapon. The Churchill MKI "gun" tank ALSO mounted it in their hull front glacis for infantry support... And in THIS application mounted the No.30 tank gun Sighting Telescope....the same crosshair telescope sight as the 2-pdr high velocity gun! In fact - its muzzle velocity was four times higher than the 3in howitzer! I also have learned that the standard "gun tank" Matildas, Covenanters, Tetrarchs and Crusaders all used the No.30 Sight for their 2-pdrs...what I'm trying to find out is did they use the SAME No.30 sight for their C.S. howitzer-armed versions??? The 3in howitzer in the C.S. tanks has a pathetic anecdotal reputation for accuracy; apart from the low muzzle velocity and short range...just over 2,000 yards...I've recently begun to wonder if that reputation was "helped" by trying to use the same sight for a low-velocity "lobbing" arcing-trajectory howitzer as a direct-fire, high-velocity, flatter trajectory tank gun??? :shocked: Can anyone help fill in the blanks???

Hi Richard - THIS is particularly intersting... Does that mean there was a contract of 500 with the increased-clearance pistons in them straight of the production line...in addition to the 1,400 that were modified for wading with the new pistons in May '44? Looks like the new pistons in Wellworthy's proprietary cast iron alloy grades provided a longterm cure then! Piston slap, yes...but no accelerated wear

Richard, here's what I mean; Tom has since been back to the "big" D.M.E. file and found THIS regarding the pre D-Day issue... Now - that WOULD indeed make it look as of only one set of vehicles, those for the assault companies, were intended to be waterproofed for wading...to wade...and need the increased-clearance pistons, as you say... ...but some time AFTER that something at Austins seem to have changed... ...and the NEW Wellworthy rings in DTD 485 and DTD 233 were going to be out into NEW 6-clyinder engines on Austin vehicles on the production line. So do we read that as Austins fitting the new-spec rings (or the War Office WANTING them to!) to vehicles that weren't intended for wading and didn't have the New "May" spec increased-clearance piston...and didn't need them..."are not having their engines re-workedas the defect is only experienced when wading"...and had been running happily on HD30 for some two years... OR... In the interim....SINCE May and the resolution of that earlier problem... had Austins at some point settled on a single piston specification - the increased-clearance one...for ALL their K5/K6 engines? I hope that explains better what I'm trying to find out

Hi Richard... No, what I meant is that from the comment from December... ....and... ...do those mean that from May on Austins were using the increased-clearance pistons for ALL K5 production??? Even vehicles that would never see any wading? If they didn't have the increased-clearance piston, they wouldn't need the new rings - the OLD spec K5 engines had been fine for several years! :-) Until the seizure-on-wading problem had materialised... EDIT: Just had a minor Eureka! moment :-D Surely we should be able to tell this from the manuals??? There should be one single part number for pistons for both GS K5s....and all K5 variants...from May 1944 on??? And this should be different from the piston part number from BEFORE May 1944 :-)

Hi Richard - that certainly makes sense! Are you aware of anywhere where this particular aspect of the problem was recorded? Or possibly - when K5s were first waterproofed for training prior to D-Day?

All - between myself, Tom O'Brien and a number of members at HMVF, we've managed to produce a VERY good timeline for the legendary problems the Austin K5 "Screamer" 4x4 suffered in 21st Army Group hands beginning in September 1944...until its resolution with new-specification piston rings in December. The BRIEF version is that the famous problems the K5 came to suffer....very accelerated piston ring wear, leading to burnt and contaminated oil; very worn valve guides and bent/damaged valves, and heavy carbon/burnt oil desposits in the combustion chamber...ALL arose from a combination of the following; 1/ a new piston fitted to the K5s prepared for "wading" in May '44; these had increased clearance for the piston skirt because (possibly) of an earlier overheating issue - which led to the pistons "rocking" and the rings wearing far too fast - in turn because... 2/ Austins used old-spec rectangular-edged piston rings on these new pistons, and they gave marginal sealing; certainly not enough to prevent accelerated wear and oil contamination, or cope with the pistons rocking; 3/ There was very fast valve guide wear, leading to BOTH oil in the combustion chamber and badly damaged valves - both because of the contaminted, heavily graphited oil AND because of local overheating - the latter possibly because of... 4/ The changeover to 80 octane "MT 80 Pool" iin service just before D-Day....which was KNOWN to cause local overheating and hotspots in some older engines, particularly ones designed to run on a lower octane rating fuel - and finally... 5/ that new, increased-clearance piston fitted in May? It very possibly led to problems with the new, low viscosity "HD30" high-detergent oil grade that had come into common use , along with other HD grades, in late 1942; this oil had prviously given no problems - but the new pistons and fast wearing rings meant that the oil film wasn't being scraped off the cylinder walls properly - leading to oil drag, increased wear in turn AND burnt oil due ti blow-by on the worn rings. The whole problem - after various attempts to find other cures - was put right at the start of December by the fitment of a new specification of piston ring that would fit in the existing, increased-clearance pistons; these rings, in a much harder grade of cast iron alloy that was a patented product of Wellworthy's, the piston ring specialists....had a tapered edge for better support of the "rocking" piston and of course wouldn't wear anything like as fast. Both the compression rings AND the oil scraper ring was revised - and because of the taper they were "one-sided" they could only be fitted one way up - and THAT side was marked...."HD30"!!! And thus the famous problem was resolved - or at least the Director of Mechanical Engineering at the War Office thought so! Obviously...any overheating due to the MT 80 could be coped with once all the piston ring wear and dirty/burnt oil issues were removed from the equation. BUT HERE'S THE PROBLEM... In May, 1,400 K5s were "recalled" and fitted with those new pistons at Austins; these lorries had ALREADY been waterproofed and issued to assault companies....and REME had to waterproof them AGAIN! So this particular activity - the fitting of the new pistons LESS THAN A MONTH BEFORE OVERLORD - must have been a rapid reaction to some OTHER problem!!! And given that it was "solved" by increasing the piston skirt clearance to allow for more thermal expansion - this problem must ALSO have been something to do with overheating... So my question is very simple - is anyone aware of, or ever heard of, problems with the Austin K5 4x4 BEFORE D-Day?

....THIS; ...this reads to be a test of a number of possible workrounds that REME in Normandy came up with to deal with the valve/top end aspects of the issue. But it was a failure :-( It looks as if none of the kludges held up to the rigours of the test...and they had tested them in the face of the worst deeds of the culprit -"this vehicle had been fitted with new standard pistons and rings". And the piston/ring problem beat the best efforts of REME with what they had at their disposal in Normandy. So...the affected vehicles REMAINED "at present frozen in V.R.Ds" until the end of the testing period on "..3.12.44..." - when "new and interchangeable piston rings of improved material and design should be incorporated into production now, and fitted to the 3,000 vehicles at present frozen in V.R.Ds". The "test period" itself had lasted from some time before the 8th of November 1944... ....to the 3rd of December 1944. And THAT was the official end of the Austin K5 problem in Normandy, as far as the Director of Mechanical Engineering at the War Office was concerned. Having found a cure that involved "new and interchangeable piston rings of improved material and design". Less blowby to contaminate the HD30 oil...which could therefore carry on being used; as could the "standard" (standard that is for the "assault" K5s) increased clearance "wading" pistons. No contaminated, heavily-graphited "dirty" oil circulating around the engine creating high wear rates in the top end. No coking up of the valves or the combustion chamber, no oiled-up plugs. And just to square the circle on the above - I doubt there is much coincidence to the fact that there were 1,400 Austin K5s in "wading" kit provided for issue before the start of June '44 to assault GT companies for D-Day according to other details that Tom found....and 1,400 Austin K5s in Normandy affected by problems of faulty parts and accelerated wear three months later; some with as little as 2,000 miles on "new" engines. It's also worth noting that Tom had also discovered and recorded on the lorry thread on ww2talk that 1,400 K5s were pulled and prepared for issue to the assault companies in May '44...by Austins themselves...I wonder if THIS was when the increased-clearance "wading" pistons were fitted??? Finally - the issue of the change to MT 80. We know from various locations and histories that this change on the eve of OVERLORD did cause problems for many british vehicle manufacturers...and that litany of valve problems on the REME "test" K5 does mention two symptoms of overheating/poor cooling of the valves - the pitting of the valve faces and the "definite signs of leakage" I.E. the valves not sealing on their seats. It's a bit "chicken and egg" whether the SECOND of these would be down to the valves burning OR the valves rocking around due to the guide wear ....but pitting on the valve faces would be a sign of overheating/poor cooling all right... One of the British Army veterans on ww2talk confirmed that the Austin manual for these engines (in 1946 at least!) DID contain instructions for advancing for retarding the ignition timing to match the fuel used...so as a problem this one was easily dealt with. But it IS interesting that Austins (and I presume the War Office!) thought it essential to fit "wading" pistons with increased piston skirt clearance to deal with extra thermal expansion A MONTH before D-Day! THAT is definitely "last minute" stuff!!! So - one set of problems brought on/complemented the other??? Need for increased piston skirt clearance due to overheating in waterproofed engines -> fast bore/ring wear 'cos the new pistons used the old design/grade of rings -> high oil consumption AND carbon blowback contaminating engine oil -> worn valve guides...which are ALSO going to be hit by overheating issues anyway because of the MT 80... It's worth noting that from everything I've read, and comments from several members on ww2talk - that while altering the timing on internal combustion engines to prevent pre-detonation etc. with higher-octane fuels is one action that's necessary...it doesn't ACTUALLY make the engine run any cooler! THAT is a problem that an engine still has to cope with....or in the case of the K5, exhibit overheating valve issues as well as worn valve guide issues. However, looking at that final closure of the book on the K5 problem as of 3/12/44 by the War Office - I think we have to assume that the overheating issues brought on by MT80 were "officially" thought to be by far the lesser issue involved compared to the damage done by the fast-wearing piston/rings issue. Once THAT was addressed, the K5s could handle a little overheating...???

Courtesy of Richard Farrant on HMVF It's not the oil scraper/oil control ring that REMOVES oil from the cylinder walls as a piston goes up and down; it's the edge of the piston skirt. The "oil control ring" makes sure a certain metered amount REMAINS on the bore! The clearance between the piston skirt and the cylinder wall was increased I.E. it was a sloppier fit from the factory - to allow for overheating and a greater expansion of working parts due to the "wading" regime on the K5's engines making them run hotter than normal In layman's terms - they arrived NEW from the factory with a what we would interpret/regard as a degree of wear already present! Within a short time, the increased "sealing" load put upon the "standard" rings would result in premature wear...and increasing carbon "blow-by"...contaminating/absorbed by the high-detergent oil, leading to the high wear rate on the valve guides...in turn leading to oil in the combustion mixture and in turn the combustion chamber I.E. "the heavy deposit of carbonised oil and the sparking plugs were heavily oiled". Richard Farrant had one more thing to note up this thread that applies to this scenario... the - So...the new rings sealed better (due to the extra pressure - I'm guessing the change in material was to make the increased-pressure rings last longer ...)... AND were specifically designed to cope with HD30 oil and its effects/attributes . And it's these modified rings - particularly I would assume the oil control ring? - that had to be fitted the correct way up as indicated by the "HD30" mark. That must therefore have been one of the "design" changes to the modified rings - whatever was changed about their design, they became "single faced", only useable/fitable one way round. And finally...

Well, first of all - ...forgive me for wondering if the K5's 3,990 cc motor was actually a two-stroke! Obviously they wanted to check the efficacy of various possible repalcement strategies depending on the results of the test; it's a pity they didn't specify WHAT cylinders each type was fitted to .... HOWEVER - what I'm seeing here, now....I should have asked before, right at the start of the thread when you first found this, Tom...is signs of ALL THREE of the problems we've been discussing! Unfortunately, the one thing I HOPED to see from the account was missing - quite literally the colour of the smoke the engine was undoubltedly puffing out by then! Blue smoke= valves and guides, white smoke = rings! As sadly THAT section doesn't specify where the oil was coming from...above or below! But THIS is the most interesting section... THIS - bu t the exhaust valve heads were distorted in all cases, and there were signs of pitting. One of the built-up valves was showing definite signs of leakage - is valves burning. That looks like the octane rating vs. ignition timing issue rearing its head... THIS - T here was excessive oil present on the guides of Nos. 3 and 4 valves - is a high wear issue I.E. the engine oil was dirty/carbonised/graphited up...I.E. the high-detergent oil was carrying blow-by on the rings around the engine, causing wear at the valve guides. There's the smoking gun all right - but it's more like " Murder On The Orient Express ", there are signs of several culprits ALL working hand-in hand Now... There's one more VERY interesting sentence in that report It's THIS ... The 1,400 "wading" Austin K5s didn't have "standard" pistons and rings fitted! To be exact - it had rings of THIS specification... ...and that was the same spec in 1943 as in 1945! So those details didn't change... But I know from Tom's work early in the thread - at the very least the material used did! AND... ...it ALSO looks like the "design" of the rings themselves changed - not only have we that comment from above..." new and interchangeable piston rings of improved material and design should be incorporated into production now "...but we have THIS from the HMVF thread - ...from - the " Austin Service Journal - War Department Issue " !!! So - THIS " Ring gap ·008/·012-in. Groove widths: Compression ·1265/·1270-in. Oil Control ·1577/·1582-ins. Groove clearance, ·002-in. to ·0025-in " remained the same, but other design aspects of the rings themselves were changed as well as the material they were made from. ***But what was it about the "wading" K5's engines that MADE these changes necessary to stop carbon "blowby" past the rings heavily contaminating the HD30 oil, that in turn was being circulated around the engine and causing the high wear visible on the valve guides???***

Guys - I might just have come up with the answer! And it turns out ot be courtesy of Some of Tom O'Brien's earlier hunting trips to Kew... Early in the history of the AHF thread where he and I did the bulk of our digging, he noted that he had come across a REME workshop report from September 1944 detailing some tentative mods done to a K5, and that lorry being tested....and failing. At the time i didn't think to query that....but two nights ago I got him to post up the DETAILS of the test and what REME found after the test concluded...and when put together with some OTHER stuff Tom has found over the years, and some of the stuff contributed to this thread by various members here - put together in the right time order! - I believe I've got an answer, and very possibly THE answer! First of all - here's the core of the REME test report - ...and here's what I THEN posted up on AHF...

Wally, thanks for that! I'll pass it on to Tom O'Brien for his next hunting expedition!

Recoverable???

In the meantime - I can move the oil issue along a bit! I've been shown a couple of pages from the REME Official History...and - There WAS a formal agreement...the Paul-Pryon Agreement - in October 1942 by which the British would move over to U.S.-equivalent "HD" detergent oils! Up to them the British were indeed using a range of straight mineral oils in the "M." series. A temporary "changeover" regime was put in place to handle the switchover period...and although it was indeed feared that the "flushing" effect of the HD oils in pre-used engines WOULD cause carbon deposits to break away and circulate round the said engines....there was no sign of it happening in practice... BUT as we now know - Austins did experience problems with their existing piston ring specifications when used with new HD oils Certainly with their car engines post-war...and from the revised-spec piston rings in the Ks being specifically stamped "HD 30" I would guess during the war too.

Hi Wally, did you you have any luck turning up anything more?

Richard, thanks for that. There may still have been a problem with the "wading" types issued to the GT companies for D-Day despite those changes...because from what Tom O'Brien has found they were replaced quite sharpish in the GT companies "this may have caused panic at the time and all K5's were considered a problem as it may not have been known how to identify which engines were wading types" I wonder if this could have been mistaken for premature wear??? OR...could wear on top of the increased clearances have led to problems faster than comparable "B" vehicles? But THIS is real bingo...! Do you know if the new rings were specified to match the HD 30 oil specification??? (Or were the "high pressure" rings used in the "wading" engines with the looser clearances???)