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Question on 2 1/2 litre main bearing bolt strength..

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tjt77
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Question on 2 1/2 litre main bearing bolt strength..

Post by tjt77 »

Does anyone know the metallurgy on the original main bearing bolts in the 2 1/2 litre V8 engines?
The ARP brand in both stainless and black( chrome moly) steel is +/- 170,000 psi.. given that almost every one of these engines Iv'e pulled down has main bearing wear and there is often evidence of main bearing caps 'chattering' on the block face (ie..the cap is moving) .. I think, minimally, its prudent to upgrade the hardware.. the original bolt design is a shouldered 'stretch' bolt.. the ARP in close sizes is NOT.. stem width same on shoulder to threads..
Any 'hands on' advice greatly appreciated..

Ive been using ARP straight shoulder (non stretch) bolts on the con rods of BMC B series engines for several years..(ARP 742-2000..12 point 3/8 -24 X 2") never any problems so far.. I did once get a breakage on an original BMC bolt though.(and have seen the same issue numerous times on failed engines) which destroyed the cylinder block. Hence the 'upgrade' has become incorporated on all non standard (increased power) engines...

daimlersteve
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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by daimlersteve »

Denis and i have replaced the rod bolts with ARP. The centre main is usually the weak point.
steve

tjt77
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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by tjt77 »

thanks Steve..my question was not about Rod bolts..but the bolts for the main bearings..the choice for ARP seems to be either 2 1/2" or 2 3/4".. factory bolts are 2 5/8".. and the longer ARP bolts (654 -2750..stainless.. or 613 -2750, back chrome moly) may not have sufficient thread lengths. to use as replacements.. but the 2 1/2" (654/613- 2500) most likely do..
I've been replacing the 'external' pair at the back that go though block to far main cap with 2" grade 8 'flange' bolts for sometime..wider head base should help..and grade 8 whilst not the toughest, are likely more than adequate..
Unsure what the original spec of main bearing bolt metal is.. they are shouldered with narrow shank and seem to be really thin compared with other engines..mains are always worn, and there is often evidence of the cap chattering.. so there is obvious movement in a part that should NOT move going on.. much on these engines seems to be 'minimalist'..and barely up to the job.. coarse thread bolts everywhere.. not at all like normal 'Jaguar' practice whereby decent sized studs and bolts are used throughout.. coarse thread bolts require extreme care when torquing to get them to correct specs..probabaly not enough metal in block and cap to go up to fine thread 7/16 studs.. which would be my preference..

Ian Slade
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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by Ian Slade »

Be extremely wary of main bearing bolts, they can bottom and not achieve a clamping torque even though the torque setting is achieved on the wrench, found this out many years ago when one bolt sheered whilst replacing a bearing, strangely the centre one, on checking there was about 2mm difference in length on the bolts, if the engine has been stripped and rebuilt or you don't know it has then screw in the bolt and ensure that it bottoms below the main cap bolt head surface.
Owner since the 70's, Genghis is slightly to my left.

tjt77
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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by tjt77 »

Ian, I am extremely wary of the main bearing bolts.. that is the reason for these questions.. Im very careful with building engines.. all threads are chased and all bolts checked for 'bottoming out'.. whilst the Turner 2 12/ v8 gave good power for its time , I'm not impressed with the strength of the lower end ( or the rapid wear rates commonly found in that part of the engine) I dont know the reason behind the holed sections on the main bearing webs cast into the cylinder block.. but it certainly is not good for overall strength.. I note that some engines (earlier) have extra bolts holding the cam gallery cover, that are secured in the cam bearing housings.( two 1/4" bolts) . others have holes drilled in the cam gallery of cylinder block to allow oil to drain back into sump ( seems to be mostly on later engines) and its a messy nuisance on the earlier engines to get all the oil ( and the crud that sits in the bottom) out when doing initial clean up and inspection.. close to a pint of black oily mess can reside in there.. after some measurmnst I do believe that 7/16 studs can be fitted to secure the main caps..for more improvement, billet caps secure by 4 bolts would be wise.. but overall the expense of building a stronger engine defies rationality or common sense..

Ian Slade
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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by Ian Slade »

I don't believe there is any specific problem with the bottom end, especially on the main bearings, we are now talking about 60+year old engines that have had many fingers playing with them. I admit that the centre main does tend to wear more than the other four but not that much and is a good point to check the engine condition when loss of oil pressure occurs. Referring to the cam box, all the engines I have had did not have the drain, when changing oil I always left the sump drain open until clear oil exited the sump, for about two years when commuting 70 miles three times a week the oil was still green (Duckhams) at the 5000 mile stage, so no grovelies in the cam box. The only engine I had a problem with was a rather tatty SP I bought that had been imported from Singapore and the engine was completely black inside the crank and cam case and required thorough cleaning with a brass wire brush on a power drill, it needed a regrind on the crankshaft but strangely not a rebore, having rebuilt it it revved happily to 7000 rpm and was continually run at 6500 rpm in competition until it picked up on one of the crank journals on a right hand 170deg bend at 90+mph during a sprint meeting, and it still drove home some 30 miles. So weak bottom end? sorry but no.
Owner since the 70's, Genghis is slightly to my left.

tjt77
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Re: Question on 2 1/2 litre main bearing bolt strength..

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Ian, these engines hold up far longer in the Sp250 than they do in the saloons..(less weight to pull and taller gearing the most likely reasons) which gave numerous problems from the get go..(the first of which,was rectified by increased clearance on valve guides to prevent the catastrophic effect of valves sticking in guides) Ive been building engines for over 45yrs.. the Daimler V8 2 1/2 lower end is, IMHO, weak, and consequently, suffers from rapid wear ( unquestionably, there are a myriad of weaker engines out there, from same period and earlier.) the primary issue being lack of rigidity in the block, inadequate mounting or strength in the main caps and narrow bearings which wear rapidly due to nominal surface area exacerbated by crankshaft whip) and low gearing in the saloons resulting in high rpms at normal cruising speed..( btw..the 'normally accepted' oll pressure for most engines is given as 10lbs per 1,000 rpms.. most of the 2 1/2 litre saloons will limp up to 40 or 45lbs if fresh..at maximum velocity the engine is spinning in excess of 5.000 rpms..often with less than 35lbs of oil pressure ..or 5,800 in the early cars.. who's engine failure rate was deemed 'unacceptable' by Jaguar, and hence the diff ratio was made taller from 4.55 to 4.2:1 by '64 )
Its also a very expensive engine to re-build properly to boot.. and original specification bearings are not currently available (OEM vandervell VP2 rated for 12,000 psi.. County/King reticular tin alloy 'bi metals' good for just 5,000psi) Ive had to replace both cylinder block and heads on one of the current builds..( total stated mileage +/- 85k) and have a good number of cylinder heads that are beyond economical repair.. part of the reason being the 'minimalist' design and tapered, cast in valve seats which were not designed to be replaceable... I doubt any of the daimler V8 engines i have possession of have covered more than 100k miles... in the saloons the intermediate main bearings are often shot by 60,000 miles .. sometimes well before that point.. (its quite common to find the much wider, rear main bearing shells in excellent serviceable condition however..and little wear anywhere else).. excess oil consumption as a result of a piston designed with just 2 compression rings and a one piece cast iron oil control ring running in Glazed bores is another common issue that reveals itself at relatively low mileage. Blown head gaskets another very common problem..
Conversely the 2.4 litre jaguar ( same gearing, similar overall weight and power output in the final versions) rarely gives any lower end problems before 100k miles and will often run to double that amount on lower end before overhaul becomes necessary....both the 2.4 jaguar and the daimler 2 1/2 tend to burn up an exhaust valve or two by the time they have covered 70-80k miles..about the same as cheap simple engines such as the BMC series .. made in the millions and most common in my part of the world in MGA and MGB..
no question its a unique, nice looking and beautiful sounding engine that produced good power for its size in the late 1950s....but it also has a lot of shortcomings that could have been improved upon and eliminated by smarter design and more development..

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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by Ian Slade »

We must agree to differ, the engine for what it was designed for is perfectly suitable, the problem is Jaguar put the wrong engine in the saloon, Jaguar has always had problems with their low capacity engines 2.4-2.8 were never as good as the 3.4-3.8 and they had problems with the 4.2, the XK engine was designed as a 3.4 and stretched to a 3.8 fairly well but either side of that it had problems. The 2.5 V8 was designed by Turner for the 1ton SP the 4.5 V8 for a 2 ton car, basically Jaguar not Daimler got it wrong, wrong engine in the wrong body, the 4.5 would have been ideal in the Mk10 or XJ6, Jaguar didn't make a body suitable for the 2.5 V8. Taking the average UK engine of the period a rebuild at 60000 miles was run of the mill, and cheap as was the V8 in its day, with our weather and 12000 miles a year the body was well on its way to dust without considerable care or replacement parts, for the USA with its better climate, greater miles covered most UK engines were unsuitable except as town cars, The USA V8's were big lazy engines and geared to cover the distances, with a V8 you could almost guarantee getting home on a long distance journey albeit may be not all cylinders. The UK exported cars to many countries and not all cars were suitable for those countries but profit was the object, had more thought been put to the suitability of the vehicles then the UK car industry would exist today instead of a foreign owned assembly plant, as I said before you bought the wrong car, it's ideal for running around with the occasional 100-200 mile run with a rebuild every 5 years as it was conceived for with cheap labour and reasonably cheap parts, however the world moved on and parts now are a fortune due to an original low production volume and labour is expensive due to very few can rebuild the engines due to lack of education in the mechanical skills
Owner since the 70's, Genghis is slightly to my left.

tjt77
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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by tjt77 »

Ian..good points made.. the 2 1/2 is not really powerful enough for the Mk2 body.. and has to work hard as a consequence.. to move the car 'off the line' the gearing was set unacceptably low for relaxed cruising on all but the manual/overdrive cars, which as we all know are very rare. ( and far more enjoyable to drive than a 3.4 jaguar whilst being similar in performance.)
The Mk10 flagship whale ( as 'project zenith') was actually designed to take the 4 1/2 litre daimler power train ..and gave significantly better performance at a considerably more 'relaxed' gait than with the most powerful version of the 3.8 inline six it was initially produced with. The Daimler v8 engine was not utilized, primarily due to economics.. high build cost and it was deemed the production facility was not large enough for prejctd volume required ( mis calculation..the Mk10 was a soft seller..particularly in its intended market , USA) .. the XJ6 was also designed for a new jaguar designed V8..but there were too many development issues, mainly relating to vibration.. which were not resolved by the time the car was about to go into production.. hence the old 1948 designed twin cam 6 was retained..and had premature failure rates when equipped for US smog regulations.. I believe there are more GM V8 powered early XJs remaining here in Ca than those with original engines.. ( I recently sold one on.. a superb '87 VDP version with an injected GM 5.7 and 4 speed overdrive auto box.. out of a '94 Camaro .. absolutely superb driving car.. 1800 rpms @75mph.. excellent pick up at any speed and improved handling due to better wieght balance with the lighter V8)
A 3 1/2 litre version of the turner V8 would have be ideal though, and could probably have been made in same dimensions as the 2 1/2..( an unusually small displacement V8.. another 40-50 bhp and accompanying extra torque would have made it spectacular) I still stand by my comments on the weakness's of the smaller Turner V8..which produce :- premature main bearing wear.. and excess camshaft and lifter wear.. both of which could be eliminated by improving the design.. I'll also state the bigger engine has exactly the self same issues.. and is even more costly to rebuild.. average 60 k mile lifespan did in fact beat the execrable ford 1172 cc side valve garbage.. which commonly managed 40k miles or less before needing rebuild.. I also recall the post '62 minor minors with the 1098cc engine getting very growly on the lower end..often at under 40 k miles.. but they continued to run another 30k miles even when 'loose'... I often dropped the sump and replaced just the centre main shells to keep them going.. Not so the tuned version in the sprite/midget.. which got a stronger crankshaft with larger diameter main bearings, pronto due to excess warranty claims.

tjt77
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Re: Question on 2 1/2 litre main bearing bolt strength..

Post by tjt77 »

Just to add on the 2.4 and 2.8 jaguar engines:- rarely, if ever any lower end issues..rarely any cam or lifter issue below 100k miles either..but it was geared same as the V8 2 1/2.. the 2.4s common weak spot was same as the 'other' larger displacement jaguars.. the first issue is usually burnt exhaust valves.. and upper timing chain tinckle, which often has a stuck adjuster, so gets left 'as is' after chewing up the verier wheel with blunt instrument...not unusual for the oiling hole for timing chain idler when to get choked up either ( time consuming to fix a it requires head removal to access) the 2.8s initially had piston problems when driven hard..exacerbated by weak fuel mixture.. resolved with an improved design piston and revised carb needle profile .
The 2 1/2 litre turner V8 had significantly more torque than the 2.4 jaguar .. but the final versions of the latter were fairly close in BHP output ( approx 7 hp less) and was vastly improved when the SU carbs and straight port head were added post sept '67.. a light clean up of porting and a little more cam lift and duration really helps improve power output.. easy to obtain 150hp + without any loss of flexibility..
As with the Turner V8, the jaguar inline six needs to be rebuilt with close attention to detail if one desires it to last.. 'short cuts' are not recommend if seeing reliability and longevity..

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