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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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#54 ·
I guess the best thing i will achieve from this is that when i quote the "its a good'un" factor on the spec sheet for my engine, i will be able to prove that i am telling the truth, LOL


Chip
 
#57 ·
lmao

No, im going to sling it into the back of a nova with an enormous bottle of nitrous and go and waste some blue ovals and japs up the quarter mile :beer:


Chip
 
#60 ·
I will get it rehoned by hand (still on a machine but operated manually not on a program) by someone i trust to do that sort of thing, then ill measure it again, if all the bores are not measuring up as 4thou larger the pistons +/- .25 thou all over then ill throw the block in the bin and start with another one and repeat the process until i have a block that is within the range i consider acceptable for this application.


Chip
 
#61 ·
Fair play to the bloke who takes that job on, putting it right once its wrong wont be easy. Done a bit of boring and honing in the past and its much easier to get it right first time than trying to fix it afterwards. Not saying it cant be done though. :)
 
#62 ·
Agreed, i certainly couldnt do it, but ive seen this guy rescue stuff before pretty well, although 2 thou is a big old difference.
Luckily the bore that is worse in terms of ovality is also the tightest bore, so at least he has a fair bit of metal to take off in order to correct it, and the ovalality isnt as bad as the tightness in this block, its far harder sorting that as obviously the honing takes it off all the way round.

Annoying thing of course, is ill be paying for his time wether he can save it or not, so i might be throwing more money at it just to throw it in the bin anyway, but its worth a go.

Chip
 
#63 ·
A load of good points well made Chip... but like Gary, i can't understand why there hasn't been a massive arguament!...

Cheers to all for great advice on the engine inspection front, esp Chip and Chris H42 lots read, and lots learnt.

Now i know who to ask for help in the future! But with my engine, think i'll leave the bottom end alone, no need to start messing with something with only 60K on the clock. I'm in the process of replacing valve stem seals, and complete gasket set.

Time is running on, i've been building the car for 6 months now, and the aim was to get it on the road for this summer... been spending many midnight sessions in the shed and garage working away. So for these reasond i've decided to leave it alone except for the seals and gaskets.

cheers, Scott.
 
#64 ·
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.
That's like saying a builder was a cowboy because he didn't bother measuring the brick sizes with a micrometer. Cowboy engine building would involve not cleaning the parts, not using new rings, wrong bolts not properly torqued, bearing caps on back to front, whatever. Cowboy suggests an deliberate intent to cut corners, not a naievety in expecting parts to be in tolerance.

The ring in that cylinder would have either broken or suffered excessive wear. This would have revealed itself at some stage. It would have been a learning experience.

As to cleanliness, everything was spotless during the rebuild. The marks on the crank were due to storage. The engine had stood in a previously rebuilt condition at Richard's place. It was re rebuilt due to concerns about dust contamination. The shells were the shells that had sat for a year in Richards place. Cranks are hard, shells are soft.

Anyway, I've just reread your first post whilst I'm sober.
but the assembly was obviously done by someone who REALLY doesnt know what they are doing, i would strongly suggest that whoever was given the job of building it should never be allowed anywhere near an engine EVER again.
I think If I'd bought an engine off someone and then found tolerance issues I would have sent them an email politely pointing out that they were lucky and in future they should check things and not assume them to be alright.
That would be regarded as sharing of knowledge rarher than the unnecessarily shoutey, slightly arrogant tone of your posts.
 
#65 ·
Tom, im sorry but you are just showing your ignorance here (oh god i feel that argument coming on now if we arent careful as thats a personal comment but i dont know how else to phrase it really), of course a brickey doesnt need to check brick with a micrometer because bricks arent subject to 8000rpm rubbing up and down against the plasterboard in the house.

To me a "cowboy" in any trade is someone who is cutting corners, simple as that.

That corner cut could be:
not cleaning
not torqueing
not measureing
using substandard components


you have to get EVERY SINGLE one of those things correct, if you dont, you will get a failure, in the case of this one, its possible it might have been spotted fairly easily yeah, because it would have almost certainly written off the piston and bore on that cylinder, so i would then have to remove the engine, strip it down, buy a new block, rebuild everything into that and then had to order a new piston from the states (custom made so nice long delay and lots of expense) and rebuild it, thats IF i was lucky, worst case is it would cause damage to the crank as well if the piston really went tits up in a big way, at which point basically it wouldnt be worth rebuilding and i would just throw the thing in the bin probably as 3 rods and 3 pistons with no crank and no block arent very useful.

Every time you post you are just confirming more and more that you simply dont understand enough about the process of building an engine to ever really undertake it in my opinion, i think you should probably ask someone who knows what they are doing if you can watch them do it, and question them the whole way through, thats how i learnt in the first place years ago.

As i said, if you dont have ALL of:
Skills
Time
Tools


You should NOT be building engines of this spec in the first place, its NOT just a cause of bolting it together, for a start, why the hell have the tops of the bores still got sharp edges from where they were machined?
Answer: because none of you involved actually know enough about building engines to understand the fact they should have been smoothed off slightly with a very fine file.

This post was not in anyway trying to put you down, i was just trying to point out potenital pitfalls, as i said, im not feeling ripped off or anything, im still perfectly happy with all the bits i bought at the price i paid for them, i was always intending to build it again anyway as i had previously read on here about the problems with the rings and i pointed out to you all when i was there that they had marked the bores from being too tight, but none of you had seen it, and when i showed the marks you all just said they were "nothing to worry about" its just "one of those things that happens with machining", well sorry but that is a complete nonsense, freshly honed bores do NOT have those sort of marks on them unless someone forces overly tight rings down them.

Chip
 
#67 ·
Cavgsi, No in this case the error with the ring gaps and the bores was so extreme that even if i were to run it N/A with only 100bhp at 4Krpm max it would STILL have failed.

I will be using it for about 450bhp probably, it was rob who was talking of possibly 500bhp from it when he had it.



Chip
 
#69 ·
Is there any chance we can get back to the technical discussion in this thread now that it has been re-opened? I was following this with great interest until it vanished - BTW this is just a bump to see if it does indeed bo back to the top?
 
#76 ·
I'm not going to fuel any futher argument, I hope while I am slumbering the night away we can be civil and return to a non personalised technical discussion surrounding the merits of checking a bought in engine before sucombing to any potential pitfalls of running it reliably as this in the past has cost me a lot of money/inconvenience.
 
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