egret Posted October 13, 2023 Author Posted October 13, 2023 I've looked at the rear most big end an it's a little worse than the centre main bearing, but nothing too bad I don't think and again look to be standard size and same vintage as the main bearings. I'm going to try and get a second pair of eyes to confirm the crank doesnt need any work then I can make a James Paddock order for all the bits. A local place called cambridge re-bores have been helpful on the phone and a couple of local area triumph people have given good reviews so they should do unleaded inserts, valve cutting and new valve stems on the big head, but I can't tell them how much to skim until I get the valves an CC the combustion chambers.
Nick Jones Posted October 13, 2023 Posted October 13, 2023 3 hours ago, egret said: but I can't tell them how much to skim until I get the valves an CC the combustion chambers. Get the valves seats done and the valves fitted before cc’ing. Valve heights make a big difference.
PeteStupps Posted October 13, 2023 Posted October 13, 2023 4 hours ago, egret said: I've looked at the rear most big end an it's a little worse than the centre main bearing, but nothing too bad I don't think Hard to be sure from photos but looks good to me. Can you feel any scores or ridges with your fingernail on the crank pin? It does look in good condition from the photo. Now you've taken that cap off I'd be interested to know others' thoughts about re-using the bolts. Personally I replaced with new, which I think is the recommended practice, but not sure how strictly necessary. One other thing I learnt - don't forget your big valve head will want double valve springs. Inlets are heavier than mk3 valves so start to float a bit on single springs over 5250rpm or so, in my experience.
Escadrille Ecosse Posted October 14, 2023 Posted October 14, 2023 9 hours ago, PeteStupps said: Now you've taken that cap off I'd be interested to know others' thoughts about re-using the bolts. Personally I replaced with new, which I think is the recommended practice, but not sure how strictly necessary. I have never used new bolts on a Triumph engine, mains or big ends. Just made sure they were good. Never had an issue even with big miles and big revs . And when skimming the head don't go wild at this stage. You're not juiling the screamer yet so leave some metal in the bank for when you do start adding big cams and the gubbins to go with it.
JohnD Posted October 14, 2023 Posted October 14, 2023 It's moderns that use "tighten to yield" bolts, where they are stretched beyond re-use. Triumph bolts are used and tightened to well within their yield point, and I re-use them. If you buy special conrods etc, they should come with new bolts, but that's not where we are here. John PS appealing as usual to the CR of SU, and its population of proper engineers, metallurgists and generally better educated people, what is the point of Tighten to Yield? Apart from making a market in replacement parts. J.
egret Posted October 14, 2023 Author Posted October 14, 2023 12 hours ago, Nick Jones said: Get the valves seats done and the valves fitted before cc’ing. Valve heights make a big difference. Well that's just saved me a big headache. Of course the valves will move once they are seated properly The machine shop did say they could do this for me, so probably worth while to save a lot of back and forth. Just had dad over to measure the big ends and they are somewhere in the region of 1.5 thou down, so all good for standard replacements. Excellent advice on the compression ratio. The engine number and triumphspitfire.com suggests that from the factory it was 9:1 (FD HE. USA high compression) On a standard mk3 cam, given that it'll likely never see below 98 Ron, is 9.5:1 underambitious, or should I be looking at 10:1? John's very useful post (https://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/ that I'm re-reading) suggests that 9.5 will need 98 ron anyway so 10 is not really much more risky assuming that the discrepancy between cylinders isn't too great. As for torque to yield bolts, I don't know but would guess this might help generate a known clamping force across a wide torque window. Maybe this helps deal with varying thread quality and oiling conditions, and poorly calibrated torque wrenches?
Escadrille Ecosse Posted October 14, 2023 Posted October 14, 2023 (edited) Regards your CR question. It depends on the extent of cylinder filling over the rev range of your engine which is a function of things like port flowing, combustion chamber work, cam lift and duration, carburettors, etc. Not simply RON number. My 1300 with a 40-80 80-40 high lift cam, flowed head and twin 40 Webers runs 10.6 CR and will cope with standard 95 RON fuel without pinking at a push. Although I wouldn't drive full chat to the 7300 rpm red line on the stuff. But that is with a whole load of other pretty extensive and expensive mods (see Spitfire Mk1 Ex-Racer Rebuild). However trying that CR with an otherwise basically standard engine and SUs and it will likely knock like crazy over most of the rev range. What I'm saying is that whatever your final destination with the engine, at this point you need to decide what cam, carbs, etc you will be running NOW and then go for an appropriate CR to match those. If you do end up going wilder in the future then the head will have to come off anyway for porting and chambering and the appropriate new CR can be determined at that point along with the camshaft, etc. Apart from anything, you can skim the head to increase the CR but you can't add metal to lower it if you go too far. If you are sticking with the Mk3 cam profile and SUs at the moment then I suggest that you don't go above 9.25 - 9.30 CR at this point. Edited October 14, 2023 by Escadrille Ecosse 2 1
PeteStupps Posted October 15, 2023 Posted October 15, 2023 On 10/14/2023 at 9:12 AM, Escadrille Ecosse said: I have never used new bolts on a Triumph engine, mains or big ends. Just made sure they were good. Never had an issue even with big miles and big revs On 10/14/2023 at 10:01 AM, JohnD said: Triumph bolts are used and tightened to well within their yield point, and I re-use them. I stand well and truly corrected! Thanks gents. Don't know where I got the idea they had to be renewed, but I shall relax about it in future
PeteStupps Posted October 15, 2023 Posted October 15, 2023 (edited) On compression ratio, my mk3 is running approx 9.5 on the standard cam and carbs. I wasn't entirely satisfied with my volume measurements so accuracy is questionable. It's a mk3 head but modified to take big inlet valves, and with some cleaning up of sharp edges in the valve throat. Edit: worth adding that I run it on 98 or 99 RON as much as possible. Edited October 15, 2023 by PeteStupps 1
egret Posted October 15, 2023 Author Posted October 15, 2023 For those interested in the complexities of bolt tension, clamping forces and how they change under load, I'll direct you to look at this https://www.steelconn.uk/single-post/2017/04/17/Preloaded-bolts-and-external-tension It's a bit counter intuitive, but a bolt in a properly designed system operating within design parameters will not experience any change in tension. So our big end or main bearing bolts should not experience any cyclical forces. That's not what my intuition tells me!
JohnD Posted October 15, 2023 Posted October 15, 2023 (edited) Thank you, egret! I am more educated, if only in specialist words such as faying, plies and exceedance. But it doesn't explain what "prying force" is, so I looked that up, and it's a force that increases the tension the bolt. As a 'pry' would if you wanted to separate stuck-together parts. Which leaves "Tighten to Yield"! Anyone? Pete, Thank you for you courtesy, I wasn't seeking to correct you, just save you and others some money! In evidence, I have suffered major engine explosion more than once, because I stress mine to the limit. It has never been a bolt failure, but the bolted parts - big ends etc, that give up. In this pic you will note the destroyed big end, but the bolts at the right could be undone from their place in the wreckage! John Edited October 15, 2023 by JohnD 1
egret Posted October 15, 2023 Author Posted October 15, 2023 A sobering image, useful for when I'm fantasizing about horsepower! One interesting thing about doing a couple of track days is that my view on what makes a good track day car has changed, it's not a race car, you're not chasing every tenth of a second. So I want a car which allows me to focus on driving hard, not one where I'm having to nurse it the whole time because I'm worried about replicating the above photo!
Nick Jones Posted October 15, 2023 Posted October 15, 2023 47 minutes ago, egret said: So I want a car which allows me to focus on driving hard, not one where I'm having to nurse it the whole time because I'm worried about replicating the above photo! Pete’s Mk3 is a good example of this. Pretty much standard, so parts are all within with original design limits, it’s just properly put together and properly maintained. He certainly extracts the full performance from it and it’s unexpectedly rapid 1
PeteStupps Posted October 16, 2023 Posted October 16, 2023 16 hours ago, Nick Jones said: Pete’s Mk3 is a good example of this. Pretty much standard, so parts are all within with original design limits, it’s just properly put together and properly maintained. He certainly extracts the full performance from it and it’s unexpectedly rapid Haha I'm blushing, thanks Nick @egret Link to part of my rebuild thread in case it's useful. After having the crankshaft etc dynamically balanced, I spent many hours with the Dremel and a set of scales for conrods and pistons. It does seem like it was worth it though, as I don't worry about revving beyond the red line (although the standard cam doesn't offer much more) 2
yorkshire_spam Posted October 16, 2023 Posted October 16, 2023 16 minutes ago, PeteStupps said: I spent many hours with the Dremel and a set of scales for conrods and pistons I took a similar approach with my 1500 engine build, took the masses of the pins, rods, pistons and rings. Then worked out the combinations that gave the smallest spread in masses, then took a small amount from inside the piston crowns on those over mass. A lot of work, but the tuner commented on how smooth the engine was - so clearly not wasted effort! 1
egret Posted October 16, 2023 Author Posted October 16, 2023 I'm hugely tempted to get the pistons out and check their balance against the conrods and swap to make the most even pairs, but I'm concerned I'll have to replace the rings then and all that comes along with that. For now, I'm going to keep focus on what I'm doing and leave any and all balancing for another time, unless anyone wants to pursuade me otherwise? Does removing pistons automatically equal new rings, or am I being silly.
yorkshire_spam Posted October 16, 2023 Posted October 16, 2023 24 minutes ago, egret said: For now, I'm going to keep focus on what I'm doing and leave any and all balancing for another time, Sounds sensible to me, one thing at a time!
JohnD Posted October 16, 2023 Posted October 16, 2023 egret, Wait and see what the bores are like, case you need a rebore. New rings needs the bores to be honed, even if you just swap pistons in the bores, but others may not agree with a perfectionist policy. After ensuring that the pistons and conrods weight the same, the whole rotating assembly, flywheel, crank damper and all, needs to be tested and balanced on a special rig, with vibration sensors and an electric drive. Your machine shop may have one, and if so they will remove metal as required to achieve full dynamic balance. YS, I take a skim on the lathe from the piston skirt to balance them. If it's not an insignificant amount in terms of piston height, then something else is wrong! Ensures that the piston is still balanced on the wrist pin (little end). I've tried and not found much success in balancing conrods, end-for-end. The position and manner of suspending the rod seems to be critical, and the differences very small, even with 'drug dealer' scales!
Gt64fun Posted October 16, 2023 Posted October 16, 2023 22 minutes ago, JohnD said: a skim on the lathe from the piston skirt to balance them An alternative is to take some out of the inside of the gudgeon pin with a die grinder. Steel is heavier than aluminium.
Escadrille Ecosse Posted October 16, 2023 Posted October 16, 2023 Balancing the major engine components is very worthwhile. Crank, flywheel, pulleys, etc need specialist equipment so you need to strip the entire engine down and pay someone to do it. Which all adds up. Conrods and pistons can be done at home with basic equipment and really just takes time. And stripping everything down. However, while all this is good fun and all, we come back to the question. What do you want from this engine NOW? 1
JohnD Posted October 16, 2023 Posted October 16, 2023 (edited) 2 hours ago, Gt64fun said: An alternative is to take some out of the inside of the gudgeon pin with a die grinder. Steel is heavier than aluminium. Weakening the pin? Never! Even if you only take a gram or two, you are leaving stress raisers in there! Unless you polish the extra weight off, but the advice was "with a die grinder". J. Edited October 16, 2023 by JohnD
Nick Jones Posted October 16, 2023 Posted October 16, 2023 3 hours ago, JohnD said: Weakening the pin? A little bit from inside each end where there’s almost no load? Nah! Anyway, the gudgeon pin is the most indestructible engine component - they emerge (sometimes through the block at high speed) from the most enormous blow-up without so much as a scratch! In my experience, factory built engines have pretty good balance. It’s the ones that have been thrown together with a random mix from several engines that are rough.
yorkshire_spam Posted October 17, 2023 Posted October 17, 2023 18 hours ago, JohnD said: YS, I take a skim on the lathe from the piston skirt to balance them. If it's not an insignificant amount in terms of piston height, then something else is wrong! I'd happily do that... if I had a lathe or access to one! We do the best we can with the tools/facilities available!
egret Posted October 17, 2023 Author Posted October 17, 2023 My brief for right now is something that I trust to get me the 50 miles or so down the M11 to get me to North London and back without excessive anxiety about being stranded. This will go a long way toward it getting used much more regularly which is the actual goal. Any easy wins I can do along the way to increase driving enjoyment and/or engine longevity will be enthusiastically undertaken, but I believe the balancing work extends this project beyond what I'm prepared to undertake at this point in time. It's still an unknown engine, so a gentle run for a couple of years to check there's no hidden issues seems sensible anyway. However, when the time comes, balancing conrods and pistons, sending the rotating stuff off for dynamic balance , checking/drilling oilways, hotter camshaft, etc. etc. will all be fair game, but will require sufficient £££ to do! 1
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