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SO glad i pulled the engine apart.

8K views 179 replies 42 participants last post by  MWF 
#1 ·
I recently bought a very nice spec bottom end off another migweb user, me being me, if im doing anything fairly hardcore i like to make sure its done right cause i cant afford to spend the money twice so i thought id strip the thing down over at a mates place where he has an excellent selection of dial guages etc i can borrow to check everything.

My god, it would have been a total disaster if anyone had tried to run it.
The actual components its made from are superb, the pistons for example i couldnt even find a fraction of a ten of a thousandth of an inch inconsitancy across all four and the biggest difference between the widest part of the largest journal and narrowest bit of the smallest journal on the crank was less than 2/10 of a thou, so i was completely chuffed to bits with the quality of the components,

Havent fully finished measuring every single thing yet as time got the better of me but as an example of the sort of extreme problems present, here are the stats for cylinder 3:
Top ring gap measured 20mm or so down the bore = 7 thou
Piston to bore clearance at top end of bore = 4 thou
Piston to bore clearance near bottom of bore = 2 thou
Those measurements taken at 7 degrees C

So that means that the ring gap at the bottom of the bore would be 7 - ( (4-2) * pi) thou, ie ZERO

ZERO ring gap and thats at seven bloody degrees, imagine what would have happened if this engine had ever been allowed to run, bearing in mind that the rings expand more than the bore does as temperature rises.

Just goes to show that no matter how much money you spend on an engine, if the person bolting it together for you is a cowboy you are only going to end up with scrap metal at the end of the day.

Thankfully the block should hopefully be salvageable as im planning on running around the 4-5 thou mark in terms of piston to bore clearance to make alloweances for the amount of heat that will be present due to the level of tune it will be ending up at, but obviously if it isnt going to come good then ill just start again with another block and can still use all the superb quality components still, so all in all im still thoroughly happy with the bits i bought, its just such a good job it was someone paranoid like myself that bought it all and not someone else blowing a couple of grand on it and then assuming it was built properly just cause it had been recently rebuilt.


Got to be a lesson in there about how important it is to check and double check everything when building a high spec engine. :beer:


Chip
 
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#27 ·
well, if its down the machining then the finger needs to be pointed in the direction of some1 who i wont drag into this but was responsible for all the work on the car up to a point. The block has NOT been machined/honed/bored/molested in any way whilst in "our" immediate possession.
 
#28 ·
Chip, this is a very interesting thread.. you've opened my eyes up to the fact that many factors which need checking when rebuilding an engine.

I have access to surface plates, various dial guages, etc... can you give any advice on how to measure what? ie: a step by step "non-idiots" guide for someone with engineering experience, but no engine rebuilding experience.

Scott.
 
#29 ·
i cant really be arsed commenting properly as its nowt to do with me, but i would possibly suggest measuring rather than calculating ring gaps since i dont get the same 0 thou answer chip does
agree with the theory of bore needs to be parallel all the way down the bore stroke tho obviously, but theres a ring gap for a reason and other rings expand for a reason too
hey ho
 
#30 ·
I would also suggest measuring. I did an initial fit and feeler gauge with my Omega rings, and got great results. All four bores consistent and top to bottom all the same.

I get an end ring gap of 0.72 and 0.75 thou gaps for an 86mm and an 88mm bore respectfully from your readings. The change in bore size makes hardly any difference to the results, but I didn't trust your first equation ;) Seems to work it out fine though. It's NOT zero, but it is less than a thou which is too tight IMO.
 
#32 ·
I was partially involved in the block rebuilding and I think the choice of words is a bit extreme TBH.

What you are saying is that ideally you should measure everything to make sure that it's right. Well, hey ho, I didn't personally measure anything. I just ensured that everything was kept very clean, properly lubed and torqued to the factory settings. I think we did a good job in that respect.

I don't think not measuring everthing immediately classifies anyone as a "total cowboy" who will turn pristine engines into "a pile of scrap". This engine is probably more special than an average rebuild in terms of clearances. I rebuilt my XE block without measuring anything except the ring end gaps. I don't feel like an engine rebuilding criminal as a result. It's done 10K since with no problems.
 
#33 ·
The ring gap at the top is just under 7 thou on cylinder 3, and the dial gauge shows a more than 2 thou difference in diameter between the top and bottom, 2*pi is extremely close to 7, and bearing in mind this was all at 7 degrees C at the time, its a very safe bet brian that the ring gap would be zero, obviously i didnt actually measure the ring gap itself at that point as it would have meant forcing the ring down there and then fishing it out again, plus its not possible to bury a feeler gauge down a bore to try and read less than a thou anyway.

Sorry if ive offended any of the people who were acsociated with the engine build, and im sure my choice of words was crap as usual, subtle isnt something im any good at to be honest, but its obvious from some of the other comments from people like Scott that the "dont make assumptions" message is coming across clearly and thats the main thing, im certainly not trying to take any sort of moral high ground or put anyone down, ive made plenty of mistakes myself over the years too, its a learning experience for us all at the end of the day.

Scott, to summarise, the main things you need to consider when building any engine are:
Things should go together easily, if they dont then there is a problem, if you snap one ring its unlucky perhaps, if you snap 2 or 3 its cause there is a problem somewhere.
EVERY SINGLE ring must be gapped individually to the bore its going down, no two bores are the same and no two rings are the same, so you cant measure one and make an assumption, and in most cases rings will have too tight a gap as manufacturers lean that way so you can loosen them with a file as its not possible to do it the other way round and add metal back on.
The best method for checking the bore is:
Get a micrometer on the piston (the one for that bore, in most cases pistons vary too), then keep the mic in place and insert a bore dial gauge (they have wheels on one end to allow easy movement) to the micrometer and zero it.
Run it down the bore, the reading on it is your piston clearance, and if it varies by more than half a thou on a serious rebuild then its unacceptable and needs to go back to the machine shop to be corrected.
Measure every journal on the crank, as these will also vary typically, check that the clearances between the journal and the bearing you are fitting to it are within the tolerances they should be, often some selective assembly where you swap rods around from one journal to another can correct slight errors here, and is in fact what most manufacturers do, ie they dont rely on machining everything equal they just machine it all fairly accurately and them measure and fit the appropriate sized rod/piston etc.

When the crank is fitted up before the pistons are in it should spin very freely (especially if you remove the end seals to check it, in which case you should be able to spin it with your fingers), once the pistons are in it should be fairly stiff but still not tight as such, sadly this is soemthing that only experience can give you a feel for and its not really possible to explain exactly what it should feel like.
When you fit the pistons, first the top of the bores should be radiused slightly when you get it back from the machine shop, they will leave it with a sharp edge, which in this case no doubt contributed (along with the ring gap) to snapping the rings during assembly.

AND FINALLY AND MOST IMPORTANTLY, keep it all clean!
If its not clean you will get scores on the bearings like ive found on this and also you wont be able to see things well enough to spot potential problems.




Chip
 
#34 ·
tomstickland said:
I was partially involved in the block rebuilding and I think the choice of words is a bit extreme TBH.
You are probably right, and honestly no offence was intended, I was just trying to get a point across bluntly enough so that we dont get threads with other people spending thousands of pounds building their engine and then never getting to enjoy it.

What you are saying is that ideally you should measure everything to make sure that it's right. Well, hey ho, I didn't personally measure anything.
Assumumption is the mother of all fcuk ups sadly.
Measure everything, then measure it all again, then start the build

I just ensured that everything was kept very clean
the bearings were full of marks from unclean assembly, nothing significant enough to cause a problem particuarly but still not ideal, and moisture has got to the journals etc so the crank needs a polish, but thats more a storage issue than an assembly one in the cause of the moisture no doubt

properly lubed
yep, correct lubricant was present on all the rod bolts etc, only minor problem was that on some of the external bolts like holding the wate pump on excessive amount of lubricant had been placed on the end of the bolts, you should only ever smear the threads not put a blob on the end, or when you tighten it up you can end up getting problems with the fact the bolt bottoms out on the lubricant and can punch a hole through if its a bit thin there, in this case although a few bolts were like that though, no damage had been done thankfully.


and torqued to the factory settings.
yep, everything was torqued up lovely

I think we did a good job in that respect.
it was "assembled" rather than "built" in my opinion, which i dont class as a good job i class it as half a job at best, it would have been fine for putting together some snotty old XE you are throwing back together in a hurry after replacing a damaged component and where you know nothing is tight cause its already done 100K miles etc, but its not fine for thousands of pounds of components that are going to be subjected to over 8 grand rpm and 500 odd bhp potentially and havent ever been together before.

I don't think not measuring everthing immediately classifies anyone as a "total cowboy"
we'll agree to differ on that, because in my opinion building an engine in a way that will guarentee almost immediate failure despite having all the very finest bits available is a perfect example of cowboy workmanship.

One final point about the engine, whoever chose the parts suppliers made some great decisions, the pistons in particular are absolute works of art, im still gobsmacked at just how perfect the parts themselves all were, its the least variance in size ive ever seen on a set of pistons or journals on a crank as far as i can remember, my friend who's tools/workshop i was borrowing made similar comments and he is the fussiest git i know. lmao

Chip
 
#35 ·
PS

The darwin award for stupidity on my engines this month so far has to go to myself still though, ive had 380 quid of maching done on a head in the last couple of weeks and then discovered i'd lost the bloody cam caps in the mean time and obviously they are not interchangeable between heads unless you start doing a lot of extra machining.

Thankfully C20LETMINI found them lurking around at his place in the end, but for a while i thought i had a very shiney expensive paper weight on my hands!

Chip
 
#37 ·
oddball, THIS engine would have failed in less miles than that for certain, especially at 500 odd bhp, i cant comment on yours as i havent stripped and inspected it, its perfectly possible to throw an engine together and get lucky, but of course it also depends on the parts used, if its standard sized pistons then fitted to standard bores honed out they are invariabley too lose not too tight if anything, which wont do anything dramatic, just shorten the life a bit.
Finally turbos are more prone to ring problems anyway due to the extra heat involved, so again the margin for error is much smaller than on yours which is in a very low state of tune indeed by comparison.
 
#42 ·
Ive no idea who built it, im just commenting on the results, 2 thou is completely unacceptable variance in a single bore on such a high performance engine, and whoever honed it should have used a dial gauge on it and then realised they had dropped an almight clanger and done it properly the second time or started with a new block if needed (not sure yet if the block will come good and still be in tolerance in terms of piston to bore clearnace or not)

the block wasnt honed by hand, its done on a machine (at 30 degrees which isnt common), so not sure if that narrows down who would have done it, but thats not really relevant anyway, like i said i was trying to point at the problems to avoid others getting the same issues, not point at individuals involved.

Also bore number 1 had 1 thou of ovality in it, ive just concentrated on bore 3 in this thread cause its the worst one.

Chip
 
#43 ·
I agree with Chip on this one.

The ring gap would be zero, in fact with that sort of power like he said the engine life could be measured in minutes not hours.

In some engines like v8's etc you may strip it down and notice the rings ends have been touching by the sign of light polishing. In fact some pistons may have cracked rings on them. The engine may seem fine but its not being pushed hard enough to just seize.

the minute you are pumping double of more power though the engine the heat goes way up and those rings gaps would close up so much the ring may break in a few places of it may just gouge into the bore. If it was driven after this had happened eventually a piston would pick up in the bore and thats it.

The bore seems to have been badly machined or honed. Dunno who done it etc but I doubt a deck plate was used.

Any engine that has had time spent on it, everything measured and built properly will last a long time, be very reliable and provide consistent long lasting power. Many engines get thrown together and they make good power, it lasts maybe 40k miles then its lost 20bhp. Ones that are built properly will give out more power and this power will not drop off, it will be long lasting, oil will be nice and honey coloured for quite long periods of time due to good ring seal etc.

Chip may be seen to be an arrogant arsehole, people who know what they are talking about on a certain subject tend to be like that. I'm like that. To me hes just annoyed by the fact the job was rushed and not done properly. What furthers gets on our wicks is so called tuning houses and other engine builders who do crap like this. Faults like these give engine builders bad names and people would rather get a new car or go down to the dealers for a new one. This takes business away from us, no business means no income which means no food on table.

Anyway hope it all gets sorted (it should) and hopefully it will be a lesson to others :)
 
#44 ·
I'm not sure lack of a deckplate would cause a tapered bore tbh - ovality or bananering (I've just made that up, now it's my word, lol) is more likely.

anyhow, seems we've avoided a big argument somehow, despite really really good odds, that is a more surprising achievement than chip being even slightly circumspect in his views.

now Chris reappears and is likewise quite unsarcastic!

wtf is going on here - see my website under 'gobsmacked' lmao
 
#45 ·
Bananering is indeed a good word gary, you seem to be the owner of that, I persoannly use bannanad.

Tapered bore would be more likely caused by a re-bore that wasn't done properly or big enough.

no point in arguing, its all facts. theres finger pointing to an extent but no one is saying 'you couldn't babysit a tree' etc.
 
#46 ·
It's not zero ring gap at 7 'c though, I only worked on the figures given, although these have now changed to greater than 2 thou change apparently. You can't afford to just round things in equations working out thou because if you round of even 0.1, that could be 5 thou. In this case you have rounded of 0.75 thou. That's not zero.

Though it doesn't matter anyway, because it's still far too tight clearly...

You see, Gary started the arguement! :p lmao
 
#48 ·
Any engine that has had time spent on it, everything measured and built properly will last a long time
Yep the building is FAR more important than the expensive components really, if you arent going to get things exactly correct in terms of tolerances etc then there is no point putting more expensive components in, they still wont perform/last as well as proeprly fitted standard gear, my mate is one of the best engine builders in the country for minis, and he reguarly outperforms other peoples engines who have far more expensive components in them PURELY because everything in his engines is "bang on" in terms of tolerances, he spends at LEAST 10 times as long on each of his engines than most "performance" mini shops do on the engines they assemble, he's bloody expensive to get an engine from, but unlike most of his competitors his engines dont end up back on the bench after a couple of thousand miles.

What people need to realise is that (all the competively priced) companies who churn out "fast road engines" etc are doing them to a price and a profit margin, not to a standard, if you want an engine built correctly you have two choices basically, you either phone up someone like SBD, and tell them that cost isnt an object at all and you want everything measured 3 times before its bolted together, or you do the same thing yourself instead, as soon as you start even considering the price of this sort of work in terms of labour, you are onto a losing path, things take as long as they take and cost as much as they cost, thats it, end of story, if you cant afford the tools to check it with properly (or borrow them from someone), then you simply shouldnt be attempting to build a high performance engine in the first place, because you are almost guarenteed to produce something worth nothing.

"Spec lists" have a lot to answer for in terms of where people want to spend their money, people want to see shiney new pistons and rods etc, and thats far more important to them than wether or not there is a difference of less than the width of a human hair in terms of bore straightness, because most of us dont work in engineering type jobs we dont realise how critical these tiny little measurements are, it all sounds so tiny that we think it doesnt matter.

You wouldnt try expect a head gasket to last if you didnt torque the bolts up properly, or expect a wheel bearing done up too tight not to eat itself in no time, and likewise you shouldnt expect rings to last if the bores arent honed straight and/or the rings gapped correctly.

Basically the moral of all this is that, if you havent got the skills/tools/time to do it properly then dont do it at all, its such a false economy to save a few hundred quid in labour and then wreck a few grands worth of components.
You cant just bolt a 500bhp turbo engine together and just hope it will be alright purely cause it has all the right bits in it in terms of pistons and rods etc.

Chip
 
#50 ·
Brian_S said:
It's not zero ring gap at 7 'c though, I only worked on the figures given, although these have now changed to greater than 2 thou change apparently. You can't afford to just round things in equations working out thou because if you round of even 0.1, that could be 5 thou. In this case you have rounded of 0.75 thou. That's not zero.

Though it doesn't matter anyway, because it's still far too tight clearly...

You see, Gary started the arguement! :p lmao

Brian, most people can see that 7 - 2*pi is nominally zero, certainly compared to the sort of numbers it should be (ie in the 10-15 thou ballpark at least) the exact numbers arent what counts really, its the fact its just plain wrong, like you say, its far too tight, it would certainly be less than zero once the temperature rises and thats the really crucial thing, going too small on rings gap is going to lead to problems fairly quickly, going negative is going to destroy it straight away.
This was actually the worst engine ive even seen in terms of the bore straightness and ring gaps at the worst point, in fact my comment at the time was that if my mrs was as tight as those rings, i wouldnt be in the garage in the first place :beer:

For the record, its the honing not the boring that causes this generally, and it will be via an exceptionally skilled friend of a friend and a hone done by hand (still on a machine but operated manually not just programmed) that i will hopefully manage to correct this not by a rebore as it would end up far too sloppy then, and if i cant correct it to exactly what it should be with this guy honing it then i will take the nice shiney new block and i will throw it in the bin where it belongs and ill start with another one.


Chip
 
#51 ·
I can see that 7- ( 2*pi ) is nominally zero, I can also see that 7-(2*pi) is not zero. lol

zero is zero and !zero is !zero thats all. You can conclude straight away that it's going to be too tight without actually following through with the math, but someone may be wondering how you got zero....

Anyway, my hats off to you for measuring it all up in the first place and posting the results! :beer:
 
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