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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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#177 ·
If you take a block to be bored and honed,

Then YOU need to chamfer / radious as needed (to prevent loads of writing stress raisers).

If the above sentance is :rolleyes: :confused:

Then take to good builder and say Build me...

This way everything should work and if it dosent,,

Buy next car with 3 year warantee.

GM stock bottom end now at 109K

> than 2% leakdown any cylinder when hot.

Thats after 65K of TRYING to kill it as an excuse to build it "properly",,

Hummm (44K previous owners) lmao

Get yer stock KKK manifolds polished ON THE INSIDE :D

DOUGAL
 
#178 ·
Rick Draper said:
...And you 2 cnuts are basically saying they shud learn from experience and not be able to check the mig archive for info on ring gaps and bore measurments. Hell i hope your rings break lmao ...
That's what you say
I say follow the correct procedures before attempting something you haven't done before. Do your homework. There are even books on engine rebuilding, I've got a few on my site even.
Someone who doesn't know that there's a critical clearance between pistons/rings/bores is not yet ready to be reassembling an engine.

PS

Using this sort of insulting language only shows your class, and doesn't exactly enhance your credibility.
 
#179 ·
Nicely thought out and well considered answer Rick. You should be proud of that.

I'll first off apologise if perhaps what to me is common sense but to others is not.

I do agree that people need to learn, and having useful information at hand is good.
However the way this thread has been written it should be distilled down to the usefull facts - and those will only take up a few lines.

I would also suggest that before anyone undertakes a re-build they go buy a Haynes manual and actually read it and understand what it's saying (it's a good starting point at least). Then they should talk through what they're intending to do with someone whose opinion they trust, and then when they have work done by other they always make sure that they, themselves, are satisified with what has been done.

Oh and I wouldn't wish anyones newly re-built engine/rings to break - not even yours Rick, but I put that down to me being a little older than you.
 
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