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Head is in the machine shop for a pressure test, 30thou skim and I ended up springing for some +1 exhaust valves.
The reason I went +1 on the exhaust is the extra diameter allows me to form the ideal exhaust seat / throat geometry I have read in Four Stroke Performance Tuning by A Bell. Worth a go, I'm interested to see if it yields any results.
Apart from the chamber deshrouding I just cleaned up the exhaust ports a bit, there were a couple of lumps and bumps in there and smoothed the intake ssr out as much as I could. It's still a tight radius but no longer a cliff edge. I also found that port 1 and 4 had a little step where they meet my intake manifold, only about 0.5mm but still, I took a bit of material out of the port to smooth that out.
I checked valve to piston clearance without the head gasket, simulating a little more than the skim I am having done to bring comp up to 9.5. With the piston at TDC the valves can be at about 4-5mm lift before contact, so the engine is interference but still plenty of room. I blued the valve heads to check they fitted the piston valve pockets nicely and they do, so there shouldn't be any contact issues with it all back together even well outside my normal cam timing.
I've cleaned out the block post machining and filed the ring gaps. Went with 0.45mm top ring and 0.5mm second ring gaps which just very very slightly below the 'circle track / drag race' for an 84mm piston.
Hopefully I will get a chance to pull the rest of the engine out the car this weekend, then I can get the new block built up in the evenings next week for getting it back in the car next weekend.
Errr well I think I have found the oil usage issue
All four pistons cracked on the thrust side skirts. I micced the old pistons and the measured at 83.89mm, then set up my dial bore gauge off the same micrometer and it measured at 0.15mm, or about 6 thou - well over spec. The bores still measure as round, as far as I can tell so far, so I think it is a machining error from when I put this engine together.
Crack in the thrust side skirt Zoomed in, you can see one side of the crack is more worn so the skirt has definitely been moving around. Bottom of the skirt is also worn. Non thrust side, only wear is right at the bottom of the skirt. View of the bore. Marked vertically but you can't get a nail in them.
On the side of the old Supertechs it states 83.94mm, I wonder if the machine shop didn't double check by actually miccing them? I didn't have a dial bore gauge or measure them back when I was doing this engine (lesson learnt - check everything yourself). It does explain a ticking noise this engine has always had - on a balanced throttle, neither accelerating or decelerating it would tick slightly. Worse when cold quieter when hot. I chased this noise through the cylinder head when i first built the engine, got a second opinion and was told not to worry , didn't sound damaging. It was probably piston slap from oversize bores, and 3 years later the rings are struggling to control the oil. The cracks are probably from one of my vac hose issues, giving them a great big thump and the skirts couldn't take it with the over spec clearance, but thanks for not fragmenting pistons!
New pistons mic at about 83.92-93 and the bores in the new block are smaller than the old block - measuring again clearance is between 3.5 and 4 thou.
My micrometer is second hand, so there is potential for it to be out of calibration, but I have used the same micrometer for all measurements and to set the dial bore gauge. As a comparison between each other it should be consistent. Certainly old block / pistons have a ton more clearance than the new piston / block.
I thought I had been a bit silly buying new pistons when I pulled the head off. Apart from a bit of soot they looked perfect from the top and the bores didn't look bad, nothing that your finger nail could pick up. I was worried I was chasing down the wrong avenue and just throwing money away. So it is slightly annoying I can't just return the new pistons and get my money back, but at the same time atleast I have found something wrong, that would cause the symptoms I experience that I have the parts to correct in the rebuild.
Aside from the bottom end I also pressure tested the supercharger gear case, to see if the seals leak. Pressure tested at +20psi in the gear case, so effectively simulating a 20psi vacuum in the rotor housing (6psi over the most vacuum I have seen) and there wasn't a whisper out of it, including when spinning the pulley.
are al 4 pistons cracked @ the oil-squirter notch?
you don't have the calibration bar for it then? (also temperature can alter measuring-sticks & it's been warm here lately - makes a change!)
Rich.
Yes all 4 cracked at the notch.
I realise I was being a bit of a numpty this morning measuring from the wrong spot (sleep deprived). 3 of the new pistons measure spot on 83.94 but one is 83.915 - I am chasing the supplier to see if I can swap that one out, because the machinist didn't measure every piston, so all bores are set for the 83.94 - the saga continues.
But the old pistons are definitely small at the measure points (not too surprising, they are cracked and that will effect it) and the bores in the old block are bigger, all around, not due to wear.
I will see exactly what clearance the old block would be at if the old pistons were 83.94 later this afternoon, but it will be a fair bit bigger than 3.5thou, so I certainly think there was machining error involved.
Whether it was that that cracked the piston skirt or if it was broken by one of the issues I had will be hard to find out, but I would think the broken skirt would destabilise the piston lead to excess rocking and poor ring seal.
The old block turned out to be at 4thou assuming the pistons used to be 83.94mm, which I think is ever ever so slightly loose but nothing mad.
Obviously when I managed to resize the piston skirts this clearance increased. Judging from when the car started drinking oil I think I cracked the pistons with the vacuum hose issue.
Hopefully I can get this small new piston sorted and get the thing back together for a proper hiding on track in mid August
The odd size piston issue is hopefully resolved. The vendor, Bofi Racing here in the UK kindly agreed to swap my set for another set they luckily have in stock.
Hopefully this set will all be spot on like 3 of the 4 pistons in the last set. I'm really happy with the outcome and big thanks to Bofi because I was expecting a long drawn out saga about it and losing all hope of trackday action in August.
I wasn't going mad, one of the pistons was a thou smaller, measured 24mm below the oil control ring as specified in the instructions.
83.94mm as stated 83.915 ish or 1thou under stated
I checked all the main bearing clearances today with the new bearings. All bob on 0.06mm or about 2.36 thou. Bit wider than standard, but same as clearances I have run in the past without issue. Need to check crank thrust then on to setting / measuring big ends. Crank rotates nice and free.
Machine shop is progressing nicely with the head, pressure test clear, skim done, intake seats tickled. Just the 3 angle exhaust seats for the +1 ex valves.
Should have that back by the end of the week then it will be a late night to build it up to check my shims are in range incase I need to have the machine shop take any material off the valve stems.
Been pretty busy so just stealing time here and there on the engine.
I've set up the big end clearances all four between 0.0017" and 0.0018".
I have also shimmed the oil pump to 72psi. This is just to help support the extra rpm that I now spin the engine too.
I got the head back from the machine shop and I'm a bit annoyed to be honest. I must have been speaking a different language about the exhaust seats and the +1 valves because they are not even close to being sunk correctly, and are about 1mm away from the old valve shim thicknesses.
They did the 3 angle but just haven't cut enough to open out the throat and seat to get the valve seat to sit around the outer edge. See pic below the outer edge of the 45deg seat is between 0.7 and 1mm shy of the outer edge of the valve seat.
I just did a quick dab of blue on one bit of the 45deg to see how far out it was. Nowhere near the edge of the valve.
Can't be bothered to take a chance giving it back to them for a week. They said before I knew there was an issue they would regrind the valves rather than the seats to bring the valves up in the head and reduce clearance. Not a chance I'm letting them take a mm off the valves.
I'm going to try to source some Neway cutters quick to do it myself so I can cut the seats and keep an eye on lash and seat width all at the same time.
I'd be more interested in the stem intrusion as this can affect spring pressure
ok, can be shimmed if low but deepening the head if seat pressure is high OR possiblity of coil-binding can be a fiddle...
Originally Posted by Tchaps
I'm going to try to source some Neway cutters quick to do it myself
I'd be more interested in the stem intrusion as this can affect spring pressure
ok, can be shimmed if low but deepening the head if seat pressure is high OR possiblity of coil-binding can be a fiddle...
The other consideration with the current ex valve to seat condition is also the bump in comp it has given me without me having factored that in with the skim I asked for.
I really just want the tip of the stem to sit within my range of shims about, 0.3mm total range because it will set the valve head and spring geometry back to how it was before, just with a slightly bigger opening for the exhaust gas. I wasn't having spring related issues, either bind or float / seat chatter at this seat pressure / spring height, I am adding in the light inner spring just for a small bump in pressure and insurance.
Originally Posted by Zed.
you win the fuckin lottery or summint?
Rich.
Ha ha noooo just the man maths is strong. I could give it back to the machine shop, and get it back still out of range, still have to buy shims and then try to grind them down myself. They won't be properly flat, and I think I would risk some wedge effect at the top of the stem trying to push it sideways as well as down. I don't mind giving them a quick sand to take 0.05-0.1mm off them, there's only so wrong you can get it, but trying to take a couple of mm out of a stock size 5mm thick shim is a different matter. It burns a load of time that I don't really have.
Or I could get a pilot and a couple of cutters from Neway, granted it will likely run me £300 but then I have them forever, or sell them, or loan them out, and set my head up back to how it was, just with bigger ex valves. It brings the issue fully under my control, and it's a couple of evenings fiddling about with the blue and feeler gauges.
The question I am asking myself currently with the head is is it going to be worth it all the hassle? - I should have probably just left it. Put the inner springs in and be done with it. But that ship has sailed.
Equally if I get this thing past 300whp I will be properly happy, learned a load and I have a nice fresh engine to enjoy while the bank account recovers.
The bottom end is built up now and back in the car. Got the new set of pistons on Friday, they all measured within less than 0.01mm of each other, so happy with that.
Before I put it back in I checked that with the head skim I hadn't moved the supercharger support brace so it no longer lines up with the bracket on the block. It's a PITA to try and resolve with the engine in the car so best to take the time now and check. It does line up and it got me pretty hyped on getting the whole thing back together. Looks pretty on the stand
The new equal size one piece pistons looking nice and new. Awww yeah!
The Neway cutters arrived, just need the pilot which was sent separately. Won't have a chance to use them this week, but I'll crack on with gouging away at the seats when I can.
I think if I can sort the head and get it built up in the week after next I should be able to get it fired up and run in for the trackday.
When I first built my head 3 years ago using the Mazdaspeed subs (I think?? I can't remember who I got them from and the email has disappeared, they could be Supertech also but can't confirm), 5.5mm Supertech lash caps and Supertech valves, even though it looked like the shim should sit into the stem of the subs, they didn't fit.
My solution at the time, and don't laugh, was to grind the tip of the valve down to 5.5mm so the lash cap fitted onto the top of the valve.
It worked, didn't cause any issues, but as I have learnt more I have always had in the back of my mind that if I ever dropped a valve, my grinding above the collet area would be the reason.
This time round with the new valves I didn't want to grind them down. I checked the diameter of the subs stem with a caliper at 5.5mm. So I thought it must just be a tight enough fit to have put me off last time, but not this time.
So I lovingly tapped the shims on with a hammer, and now I can't get them off. I was checking the intake lash and of course it needs changing about (not too much, but enough).
Tried a bit of heat etc, but they won't budge, apart from one of them oddly. Anyway, I'm sure can build a puller tool to get them off but I'm not sure I have the time to do that, and sort the exhaust seats. It is increasingly feeling like the best plan would be to clean up the spare BP4W and get that on the car, and take my time getting the new head right, as incredibly annoying as that is.
if so easy to make a crowsfoot adapter to fit a slide-hammer
Rich.
No not a lathe but I can make a puller without too much difficulty. I bet either a slide hammer or screw type puller would have them off in seconds, however pliers will not and I don't have time to make the tool.
Also I found one of my intake lashes has expanded to about 0.75mm, up from 0.2mm. I've checked the valve length, shim, bucket and cam and they all measure in spec. F knows what is going on there but it all just points me in the direction of don't panic, don't rush, run the spare head for a bit while I sort the fancy one. Swapping it back over later isn't a particularly difficult or time consuming job.
It will also be an interesting comparison, get some data from a stock BP4W, boost pressures and power. Then swap on the 'improved' head when it is ready.
Back from hols now so back on getting the car up and running for the trackday on the 19th August, clock is ticking.
I have taken the spare head apart to give it a proper clean up, glad I did it was full of crap from sitting around.
Other than that it all looks fine. I have given the seats a little tickle with the new 45deg Neway cutter. Works so nice and easily.
I got the expanding 6mm pilot, it slips into the guide and expands to form a very secure centre for the cutter.
The cutting tool works nicely with a bit of pressure. I am just using a T bar at the moment to turn so you have to be careful to release the pressure as you stop turning to avoid any gouging.
I lapped in the valves after and they have come out well.
I will put it back together with the Supertech light double springs and retainers, but the stock nb solid lifters. I have a load of shims for these I share with a mate so will be able to a correct some of the slight lash imperfections I measured before disassembly and also correct if the very slight recut and lap has closed any lashes too far.
Should be able to get the head back together over the next couple of evenings, then back on the car for first start sometime over the weekend. Get some miles on it then drop the oil just before I drive up for the trackday.
No pressure
On the fancy head I am going to take my time with it, and probably start again from one of my other BP4W castings. There are a few things I think I could do better with a second roll of the dice.
I also want to get a basic flow bench up and running to step by step see the effects of every change, from stock to modified.
Cylinder head and supercharger are all back in the car, all timed up, lash set ready to rumble. Turned it over without the plugs in and got oil pressure so all looks good so far.
Should have it fired up tomorrow.
However I found today that the clutch hydraulics have given up in the time sat doing nothing the last month
I thought I had gone mad and put the clutch plate in backwards again, despite me checking it a million times when I installed. But I got a neighbour to push the clutch pedal with me under the car and the slave wasn't moving so its the slave and or master. Slave was a little wet but it's not pissing out and when I tried to bleed the system it didn't feel as it should with the master. I've ordered replacements for both, not going to muck about with only a week to the trackday.
No pics at the mo, my phone is broken, need to sort that too.
07-23-2021, 05:47 PM
1
, didn't sound damaging. It was probably piston slap from oversize bores, and 3 years later the rings are struggling to control the oil. The cracks are probably from one of my vac hose issues, giving them a great big thump and the skirts couldn't take it with the over spec clearance, but thanks for not fragmenting pistons!
that's quite a collection of vices!
I was checking the intake lash and of course it needs changing about (not too much, but enough).
