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MG Midget and Sprite Technical - Picked up my head
| For those not on the FB groups... I dropped in to Peter Burgesses place on Friday to pick up my "new" head. Always fun to stop by and chat geeky engine stuff for a couple of hours.
The head now has: - Bigger inlet valves (1.44" was 1.38") - Four angle valve seats. - Hardened exhaust seats (for unleaded fuel). - Bulleted bronze valve guides. - "Uprated" TR6 valve springs. - Skimmed to give approx. 10.5:1 compression ratio. Should be the last piece of the puzzle on my engine! Booked in for another go on the rollers in May to see what it will do. Place bets now? Huge thanks as always to Peter. Malc. 
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| Malcolm |
Valve seats and backs of valves
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| Malcolm |
Bulleted guides and ports that I DIY cleaned up a few years back.
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| Malcolm |
| Hi Malc I would query what the each of the valve seating widths measure following final lapping as final cut on seat is usually used to control. Also, has level of valve sealing been measured ? Cheers |
| S G KEIL |
| Not sure Steve, but I trust it is right! |
| Malcolm |
| Wouldn't even think of questioning that knowing where it was done---looking good Malc. |
| William Revit |
| Malc, your earlier comment about TR6 valve springs intrigued me. I didn't know they were different to the 1500s usual springs.
I've not heard of doing this before although I have a fair bit of history with Triumphs (albeit mostly the sixes). Do the TR springs have a higher rate to allow for higher revs without valve float or do they allow for higher rocker ratios for more lift? I'm interested because I'm looking to get hold of a used 1500 engine to rebuild with a bit more compression, a livelier cam and a bit of blueprinting and eventually swap for my original which is starting to show signs of getting a bit tired. Edit: and a Peter Burgess head of course! |
| Greybeard |
| Hi Grey,
Peter didn't give me the full details, just mentioned in passing that they were later TR6 springs. Apparently they are less likely to end up with coil bind at high lift (although I never thought it was a problem with standard springs, but I might have been ignorant!). I can see that they are wound a little differently and done away with the the little collar thing under the spring. But know nothing more than that. Sorry! What sort of cam and the like are you thinking of? Cheers, Malc. |
| Malcolm |
| I believe it best to get any "non standard" work e.g. head modifications done by a specialist. I had hardened seats and bronze guides fitted to my MG TF by an "old fashioned" machine shop. The job looked to be fine until the valves started sticking. They had reamed the guides to cast iron tolerances and bronze expands more, hence the sticking. Jan T |
| J Targosz |
| Not sure yet Malc. I think there might be benefits from using an earlier small bearing camshaft and bearings from a 1300 Spitfire as the 1500s cam runs directly in the block. A notorious source of rattles given the engine's fairly crude oiling system.
A set of bushed rockers with a little more lift might help the breathing too, given that the engine was stroked up from 1296cc to 1493. I don't plan anything exotic and anyway it will have to wait until I get chucked out of my job later this year when I get too old; I don't have the time to spare now. Right now it's just speculation. |
| Greybeard |
| Knackered cam stopped play at the weekend (doh! the head has been off for six weeks and never checked until Friday afternoon).
Grey, I bushed the rockers years ago. I can't remember who machined them out, someone on the BBS. Then sleeved them with a standard size bush. Easy and cheap to rebuild. Never found the cam bearing thing an issue. Certainly not the worst part about the engine! For "not too exotic", the Piper 270 cam (similar to the standard mk.3 Spit profile but a bit more lift) makes for a decently punchy engine. 88hp with carbs, dizzy, the mk.3 spitfire (cast but four port) exhaust manifold and minimal head work (three angle seats, skimmed to 9.5:1, dremel-ed off any casting flash in the ports). 
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| Malcolm |
| Malc. not sure if you're aware, but here goes anyway.
You have to be carefull to get cam followers that are compatible with your cam These 1500 engines in std form have the lobes ground, flat (for the want of a better word) and the followers are flat as well with the camshaft slightly offset to the centreline of the followers to promote spinning Most aftermarket cams are ground on a slight taper and the followers to suit them are finished slightly convex to match- It's super important to have the followers the right shape to suit whatever cam you get otherwise the lobes and followers cop it and don't last long at all- willy |
| William Revit |
| Hi Willy, Only one lobe has suffered, seven others are absolutely fine so I don't think anything intrinsically wrong with the setup, but more a "random" failure in a part or the bedding in process. We live, we learn. New cam and lifters ordered and we will move on - it will be a car again one day! :-D Malc. |
| Malcolm |
| As always, good to see you Malc.
The springs are the late TR6 doubles ( most expensive to buy in too!), the brilliant thing is they need no inner collars and seem to allow a little more lift so no messing about hoping you get the correct collar spring combo, get it wrong and knacker the cam or snap the tip off the valve if coil binding occurs! Jan. The new TF valves have 8 mm stems from the suppliers and need the guides reaming to 8.03 mm or they seize up even in CI guides. The original guides only needed to be 8 mm reamed as the valve stems were narrower, the sad thing is there seems to be clearance until measured or when they are run and seize in :( |
| Peter Burgess Tuning |
| I forgot to reply to Steve. I use a 3 angle carbide valve seat cutter in my Mira seat cutting tool, 30/45/60 . In this case the 45 seat was 1.5 mm ( I have cutters which will give 1, 1.3, 1.5, 2, 2.5 and 2.75 plus 30 and 60 cuts depending on the application, I also have 20/25/30/35/45/55/60/65/70 and 75 individual single cutters if need be. Some heads have 35 degree valve seats!) which is fixed so lapping makes no difference to seat width, just confirms seat laps ok in head and on valve. I then use a 75 degree cutter to reduce the 60 degree to around 0.5 mm, I then hand blend the throat to achieve a nice radius into the 75 degree element of the seat and achieve the desired ID of the valve throat.
If need be I have SP Nuway single angle carbide insert seat cutters at 30/31/45/46/55/and 70 degrees for restorative work. For really hard modern inserts I use an orbiting eccentric grinding seat cutter made by PEG. I can dress a stone to any angle I like. On competition motorcycle single cyl heads which rev to silly rpm we use the PEG then blue the seats. The valves are titanium and have a coating which would be destroyed by conventional lapping and only last less than one hour, the blued seats run 10 plus hours. What I find amazing is the inlet valves die before the exhaust valves which is opposite to what we are used to with 'normal' engines. The inlet valve being larger than the ex valve weighs more and it mushrooms before the exhaust valve. This can be alleviated to some extent by fitting ally bronze seat inserts ( used in olde worlde ally heads) The softer bronze cushions the return of the inlet valve to the seat and causes less damage... horsepower costs money, how much did you want to spend sir! |
| Peter Burgess Tuning |
| Now you've got me intrigued Peter---
With the mushrooming of the valve are you saying the head of the valve inverts or just the outer edge turns up-reason for asking is i've got a 6-7 year old chev to reco/detune, it's done a 'lot' of competition and runs 2.3" titanium inlets and 1.75" inconel exh.---it's never shown any valve clearance closing down issues but I guess the valves have got a bit more meat on them being the size they are compared to racing motorbike valves---From what you've mentioned I think going a new set might be the go, just in case. as you say, it's only money----lol willy |
| William Revit |
| Hi Willy, I am not sure if it is purely the revs or the material. I understand titanium reciprocating and rotating components are prone to failure so not ideal for longevity. Light weight short period. Particularly true in titanium valve caps.
The bike we do heads for most is KTM sxf 250. 39.8 hp at 13,400 rpm and 19.1 pound-feet of torque at 8,700 rpm. rev limited at 14000 rpm Greybeard, the springs we use are 67-71 up to engine CP54584. TR numbers 149633 outers and 102564 inners. They aren't as strong as Spitfire doubles 157229 outers and 157476 inners, same coil bind heights, so it looks like trade main reason for fitting is ease of use not having to try and match up inner spring collars and the fact TRs can eat cams with stronger springs. Quite a few companies use std springs in race heads if lift is safe. |
| Peter Burgess Tuning |
| Cheers Peter
When we first got this Chev engine the warning was don't give it any stick cold or the heads will drop off the valves-apparently the story was cold titanium is brittle until it warms through- we've always warmed it right up and never had an issue so will continue doing what works---it'll be interesting to see what condition it's in when it comes apart -i'll be having an extra good look at the inlets now but because of their age i reckon new ones will be the go anyway---the guy that owns it wants it detuned a bit so he can run it in a sealed road rally car, the thing's almost undrivable as is, he's been struggling with traction issues for years and wants to drag 100 or so HP out of it---goes against the grain a bit but his car his money- willy sorry 'bout the thread drift Malc. 
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| William Revit |
| Drift away! It's all way more interesting than my fairly tame old tractor engine! :-) |
| Malcolm |
| "we've always warmed it right up and never had an issue so will continue doing what works"
That took me back Willy to my Alfasud days as they had a warning light which extinguished when the engine was up to temperature, only then you should then give that little flat four some stick. Cracking little engines they were too. That taught me to allow engines to warm up thoroughly and even now I cringe when hearing people rev a cold engine. Enjoying the thread even though I don't understand the half of it🙂 |
| Jeremy MkIII |
| Malc
Great news on the new head from Peter. Rough news on the cam etc It can be what makes these old cars ‘fun’ to work on. Apparently. To cheer you up, finally just got my own garage with power and light. But up and over door does not lock due to u/s automatic opener installed by PO. So I source and retrofit manual lock bars and catches but now I cannot open it - the new catches and bars release, just the central top latch mechanism that connects with the auto opener now seems to function when it did not before! (I thought I had disabled it). This all happened on the first test with new bottom bars and latches, with the light on and my boot of road car tools in the garage which has no side door or windows. ‘My friend’ will be applying a drill/jigsaw/angle grinder to the situation from the outside to remove the offending central top latch attachment and then putting in a repair patch to the the door. Can then move in the Sprite, rest of tools and get on with fixing the car and readying for sprints/hillclimbs. Move forward one space, back three hundred! Aaaargh! Mike |
| M Wood |
| Hi Peter, You have confirmed what I said in my post. The guy who did my TFs head, works on modern engines and probably didn't have data for an EXPAG. I suspect he just used "feel" rather than a micrometer. With a Classic it's best to go to someone who understands them. Jan T |
| J Targosz |
| Willy, your comments about the titanium valves struck a chord in my memory. We tried Ti inlets in the 70s in two valve speedway engines and quickly abandoned the idea because they were breaking up, although I don't remember any heads actually separating completely. Now I wonder if it was a temperature problem as you said. These engines were burning methanol and never really got properly hot. |
| Greybeard |
| Woop, new cam is here (Piper said 7-10 days when I ordered, but it's arrived in two). Have new followers, the uprated sort, tufftrided and with the extra lube hole. Not sure what difference they will make, but I'm going all out and throwing money at the problem to hope it is fixed once and for all! Malc. |
| Malcolm |
| Brill Malc, plenty of time before the dyno session. May I suggest you put some moly paste on the lobes and follower faces? Peter |
| Peter Burgess Tuning |
| Hi Peter, I bought some of assembly lube/grease that Piper sell. I will be using that. https://www.pipercams.co.uk/product/sachet-of-cam-lube Cheers, Malc. |
| Malcolm |
| Malc. just a suggestion- don't know if there's any issue with valve travel but New cam (with more lift i suspect), and headwork together, When you get it together it'd pay to check you have some extra valve travel remaining at full lift, your cam failure may have been the result of a bottoming out situation maybe----or not and check all of them not just one |
| William Revit |
| Cam is in! Timing cams always makes me twitchy, I don't know why. However many times I check everything I am always nervous I have got it wrong! Thanks for the tip Willy. Should be OK, but I will check in due course. I only want to do all this once. It's the same cam profile as I was using before btw. 284 degrees with 0.414" valve lift. Stock 1500 cam is 256 degree 0.35" lift for comparison. Cheers, Malc. 
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| Malcolm |
| >>However many times I check everything I am always nervous I have got it wrong!<< I've had that feeling many times myself. It goes away when you see that everything works as it should but it does keep you wondering. |
| Martin |
| Todays problem/hold up... I have run out of adjustment on the rockers. Seems I need shorter push rods. Oh well, it's only money! I guess I will have to go back to work next week! ;-) Malc. |
| Malcolm |
| Can you shim the rocker posts Malc? |
| Peter Burgess Tuning |
| Hi Peter, Surely this upsets the rocker - valve geometry? As the rockers bolt to the top of the head their relationship hasn't changed. It's the rocker - cam dimension that has changed, so change push rods to suit?! Or am I missing something? Malc. |
| Malcolm |
| With heads skimmed loads and/or blocks we find shimming the rocker posts restores the geometry. |
| Peter Burgess Tuning |
| Malc Don't really want to jump in the middle of this but if you decide to go shorter pushrods the Triumph 1200/1300 pushrods are 1/16" shorter -part no.-111874 Rimmers or someone would have them i'd think. |
| William Revit |
| Thanks Willy, they are already in my basket :-)
Rocker geometry is not something I have particularly thought about before... but pondered over night and came to the following conclusions (which are probably pretty obvious to anyone that has thought about this before!) 1. With a higher lift cam, you are sweeping through a larger arc with the rocker. If your rockers are in the standard position to start with, your arc will end further round, i.e. further toward the rocker side of the valve tip, so shimming the rocker gear up offsets that sweep back toward the centre line of the valve tip. Desirable in my case. 2. The rocker to cam geometry does not change the rocker to valve geometry, but shorter push rods would also be desirable to bring the relationship back to as it was designed. There has been about 90 thou taken off the head from standard. Shims are 30 thou, so there is still 60 thou difference from how it was designed... Oh look... the alternative pushrods are ~60 thou shorter (1/16")! Perfect! I am buying both and going to have a play and do some learning! :-) |
| Malcolm |
| Malc.
Your point 1-- "1. With a higher lift cam, you are sweeping through a larger arc with the rocker. If your rockers are in the standard position to start with, your arc will end further round, i.e. further toward the rocker side of the valve tip, so shimming the rocker gear up offsets that sweep back toward the centre line of the valve tip. Desirable in my case. " 1. With a higher lift cam, you are sweeping through a larger arc with the rocker.-------------correct If your rockers are in the standard position to start with, your arc will end further round, i.e. further toward the rocker side of the valve tip,--------correct so shimming the rocker gear up offsets that sweep back toward the centre line of the valve tip. Desirable in my case. "------------------umm--not convinced----the rocker shaft will be sitting higher to start with and this means the whole arc of the rocker will be lower/further around----unless of course the valves have longer stems which a lot of higher performance valves have The aim for proper rocker geometry is to have the centreline of the rocker shaft, the centre of the ball on the adjuster and the top of the valve stem all at the same height at 50% valve lift |
| William Revit |
| Well... here are the results! Not what I was expecting at all. But this is why we mess and learn. Might need your glasses on to see the patterns. I don't have any blue, but found Sudocrem (nappy rash cream) works well for these jobs! Albeit the colour contrast isn't great. Malc. 
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| Malcolm |
| Seems shims and the long push rods give the most centralised pattern. I was ready to chuck the long ones in the bin without even trying them! Cheers, Malc. 
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| Malcolm |
| Another go with shims and long push rods. This time setting up and testing all eight valves. I am going with this unless I hear any great objectives from the knowledgeable throng! (The pictures are the same, but on the second one I highlighted the witness marks in red). Also, clearances on the push rods seem OK and approx 0.07" between valve spring coils on full lift. Seems like plenty enough? Cheers, Malc. 
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| Malcolm |
| Malc.
All good then with the shims There is a slight misunderstanding of what should be but your pattern is good on the valve stem at that, Just to say---If you have the shims in there for both tests(long-short pushrods)the pattern will be the same, it's not the pushrods changing the pattern on the stem 'it's the shims. The pushrods are a completely different area. but that doesn't necessarily mean the geometry is out but hopefully triumph got the rest of it right and all will be well---------- Just to explain,--To determine pushrod length on an engine like yours with the valves at 90deg to the head face--now that you have determined that your stem pattern is correct with the shims fitted. The method is ----Set valve clearance to spec, then wind the engine over and measure exact total valve lift-then wind it again until you have exactly half lift---At this point the centreline of the rocker shaft and the estimated centre of the ball on the rocker adjuster should be exactly the same height above the flat head surface--- If it's out by any more than say .060" then different length pushrods should be fitted so the adjuster can be moved up-down to correct it- Also while in this half lift position, if the valve length is correct to suit the rest of what you have done with shims etc, the top of the stem should also be at this same measured height. Having said this there's probably not a lot of cars running around with perfect rocker gear anyway but while you're playing it's interesting to check- You have corrected the main issue with the shims making the rocker contact the centre of the stem giving less load/long life for the guides which is probably the most important part for a road car willy |
| William Revit |
| Thanks Willy, always appreciate your input.
Shims are for sure the way to go for a good stem pattern. So it's just a question of long or short push rods. It looked to me like the short rods moved the pattern slightly to the rocker side of the valve, but that might just be variances in my quick test and or the valve I tested on etc. I couldn't visualise how the change in rod length might cause that so just took it at face value. I shall have another play with the shorter ones and my dial gauge tonight. I have come this far, let's get it spot on. Also, part of me wants to find a justification for fitting the short ones just because they are new!! Cheers, Malc. |
| Malcolm |
| Some more messing tonight... and I have come to the conclusion that "it'll do"! I've spent two evenings messing with the rocker geometry, and whilst it has been interesting to learn about I am not that fussed that I need to spend more than the two hours spent already to find the last 0.1% of performance! Added to that, I don't think it will ever be perfect anyway.
So... all the following is SHORT pushrods and shims under the rockers. Most stuff rounded to 0.1mm this wasn't super precise laser measured stuff! Theoretical valve lift: 10.5mm Height of valve tip above deck when closed = 43.8mm Centre of rocker shaft above deck = 41.3mm So... first observation, if I want the valve tip and rocker shaft centre to be level at half lift I theoretically need the rocker shaft to be 38.6mm above the deck. That would mean removing the shims PLUS removing another 1.9mm from the rocker pedestals. Not practical, and also my no-shim test showed up a crap swipe pattern. On to actual measured values: Full valve lift (measured with dial gauge) = 10.1mm I notice this is 0.4mm less than advertised, but I wonder if the advertised value is a theoretical value? So you take the lash off that (12 thou = 0.3mm) I am about there? So valve height above deck at measured half lift = 43.8 - 5.05mm = 38.75mm. Which I set on my digi caliper to try to make observation and pictures easier. Valve and push rod side shown in the pictures. The pushrod side seems a bit higher than the valve, but longer push rods would make this worse, so sticking with the shorter ones. 
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| Malcolm |
| ... and did another check on swipe patterns with the short rods. They seem fine. It's a bit tricky to take a good picture of them with the light in the garage/camera flash, so I messed with the contrast to try to show it better on a screen. I'm calling this done as I have bigger jobs to be getting on with :-) Cheers, Malc. 
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| Malcolm |
| Good stuff Malcolm, I can see you've got a handle on how it's all supposed to work now.
As you say, it's close enough, there's plenty of cars running around way way worse than that. The main thing for a road car or any car for that matter is that nice central pattern on the top of the stem -which you have. You could go ahead and machine stuff to get the rest of it perfect but in reality from where you're at to perfect there'll hardly be anything to gain---It's close and will work fine-To be honest it's a lot closer than i thought it'd be. and with a std. lift cam it would be almost perfect in std road car trim- Random observation-pub talk OK -It's been decided to run as is with the spacers and the shorter pushrods---all good---finished Just a couple of things to add to your list of things to remember sometime at the pub. IF this engine ever got itself some roller tip rockers the current rocker shaft height would be almost perfect(for this lift) without the shims as the height of the rocker is measured at the centre of the roller not at the end of the valve stem, then a set of rockers the correct length to get the touch patern in the centre of the stem. Other thing is even as it is now with the short pushrods, they 'could' even go a bit shorter going by the pic., but there's a balance when using std. rockers (bit of a rock and a hard place thing) as it's not a real ideal to have the adjusting screws poking way out the bottom of the rocker, it looks pretty good as is in that area. The other thing is the patern on the stem. In an ideal world the patern needs to be as you have it now right in the centre, but if one day in the future you feel the need to revisit the std rocker gear then the plan would be as you have noted, machine the bottoms off the pedastals to get that centreline height matched to valve height and shorter pushrods again to get their height matched as well---I can hear you saying that'll screw up the touch point on the stem, but if you were going to all the trouble of machining the pedestals, new pushrods again etc then the fix for the stem is to re-arch the curve of the rocker tip (further out in this case)to get the touch point dead centre on the stem----------The net gain of doing all this would probably be zero all up when it's as close as it is now but I find this stuff really interesting to think about specially when you get into really angry high valve lift cams where everything is critical for performance and life expectancy. Shout yourself a beer ,you've done well, most people wouldn't even bother measuring it up--- willy |
| William Revit |
| mmmmm.... beeeeeer.... |
| Malcolm |
| It's been a while since an update... I have been continuing to work on the car, there have been so many little jobs and tidy ups going on. Slowly slowly chipping away. Too much to list, but a few of the more interesting bits to show off...
Exhaust off, cleaned up and manifold re-wrapped. I put so much effort and hours into the design of it, making it "just right" and making all the runners the same length I just like showing it off! :-D Inlet manifold mods finished off today. With the extra appendage to try to encourage more flow to the back two cylinders. It's not perfect and not "beautiful" but hopefully does the trick. Test fitting it, it also aids the packaging somewhat as it moves the throttle from behind the radiator so it can hopefully pick up some cooler air. Cheers, Malc. 
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| Malcolm |
| Well... it fired up and ran yesterday! :-D
Did about 10 mins of raised rpm for cam bed in before I realised I was on a path to cooking it! Doh!!! 1. I hadn't been paying attention to the coolant and the level dropped quite a way as air circulated out the system and 2. I forgot I hadn't wired in the radiator fan! However many times I do it, the first start sure is stressful and there is a lot for one person to have to do and check! No lasting damage I don't think though, caught it before it went into full meltdown. It had a real "punch" to the exhaust note :-D Malc. |
| Malcolm |
This thread was discussed between 07/03/2023 and 08/04/2023
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