Valtra
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 posted on 8/11/08 at 06:34 PM |
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Compression
On a real downer this afternoon . been out for a blast on the first decent opertunity for ages ....all good ...cars ignition behaving ... no fuel
issues... then I thought must check compression while it's warm ...not too good 
When I rebuilt the engine last century I replaced the rings and thought it not vital to hone the bores , I just gave them a good rub down with emery
paper ..... I can see jaws dropping , and hands slapping foreheads as I write
When I first started the engine there was a lot of crank case smoke and oil seeping out the dipstick tube where it meets the block . I contacted Guy
Croft the Fiat TC Guru and he said it may bed in ...or more likely it wouldn't and said leave it for a few hundred miles then check the
compression and if it was 180-200psi it was fine .
Car is now running so much better following serious ignition problems initialy and there is much less smoke from the crank breather and less oil
seeping out .
BUT compression test showed around 100psi  . supose my question is how long should I give it to bed in before I rip the head off (ARGHGHGH) and try
to remedy what should have been done in the first place . car has done 330 miles so far and everytime it goes out it feels a bit livlier and cleaner
running . Problem is winter is coming and the chances of me getting many miles in before the spring are minimal but if it gets to March and then I
still have no compression I could be all summer getting the engine back how it should have been in the first place
If nothing else take this as a lesson not to cut corners , but any advice would be greatly apreciated.
Ian
"If it looks like it works and it feels like it works, then it works"
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Howlor
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| posted on 8/11/08 at 06:37 PM |
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I'd have thought about 2K really.
Steve
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Valtra
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| posted on 8/11/08 at 06:44 PM |
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bout another year then .....
"If it looks like it works and it feels like it works, then it works"
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mr henderson
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| posted on 8/11/08 at 06:51 PM |
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Are you running a PCV system? Did you seal the dipstick into its hole? Is the engine running well otherwise?
John
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omega 24 v6
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| posted on 8/11/08 at 07:09 PM |
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You did check the compression with a wide open throttle didn't you??? Not trying to teach you how to suck lemons but it's an easy and
common mistake.
If it looks wrong it probably is wrong.
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mark chandler
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| posted on 8/11/08 at 08:30 PM |
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Nothing wrong with scratching around with a bit of emery, once its all back together you need to do a number of full power bursts to break in the
rings at different engine speeds.
Full power applies maximum pressure on the rings to the cylinder wall, so 5 seconds of this then foot off the loud pedal for 20 seconds, rings relax
and oil lubricates, you just repeat this for an hour or so.
That aside if the compression is the same on them all you are okay.
Regards Mark
[Edited on 8/11/08 by mark chandler]
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oldtimer
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| posted on 8/11/08 at 08:32 PM |
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If all the above suggestions get you nowhere is it worth swapping the oil for some running in oil and run it in under load to see if the rings really
will seal?
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02GF74
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| posted on 8/11/08 at 09:02 PM |
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for olding engines, crossflow, pinto, rover v8 there is nothong wrong with doiong the honng by hand - applying crosshatch to cylinders with 600 wet
'n' dry.
more modern engines e.g. zetec are built to much closer tolerances so need a 2 stage hone with proper honing stone tools.
pitson rings shold be replaced but I am not convince this is necessary since the roughed up bores will bed the rings in - the rings will get a bit
smaller but I cannot see that the change in size is significant - waiting for someone to say that this is significant and can orivide some data.
runnning in - search my post aboiut the US geezer - but basically you need to give the engine more and more load within teh first few hundred
miles.
if rings are gone, squirt oil into the bors as this will form a temporary seal and measure compression again. it could be worn valves.
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rusty nuts
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| posted on 8/11/08 at 09:06 PM |
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Give it a bit of wellie , running in doesn't really do engines a lot of good with modern oils . I remember reading an article in CCC or some
other mag suggesting that pistons/ rings should be fitted dry to aid bedding in. Tried it once on a hot Mini lump that pulled like a train and
didn't use oil so maybe it works? Did you get the bores measured? compressions should be taken with the engine hot and wide open throttle as
already suggested. Cylinder leakage test may be better than a compression test.
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ashg
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| posted on 8/11/08 at 09:49 PM |
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compression tests on a fiat tc should be done with a teaspoon of oil down the spark plug hole!!!
i have a copy of guy crofts tc engine manual if you would like to borrow it but i want it back or i will hunt you down as its worth about £300 now its
out of print!!
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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rusty nuts
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| posted on 8/11/08 at 09:53 PM |
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Testing compressions with a tea spoon of oil down the bores will raise any compression readings . That is why the correct procedure is to do a
"dry" test first followed by a "wet" test. If the readings increase by over 10% (IIRC )the bores/pistons/rings are worn.
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owelly
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| posted on 8/11/08 at 09:55 PM |
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I have a low mileage Fiat TC that I could be persuaded to part with if you need it!!
http://www.ppcmag.co.uk
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Valtra
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| posted on 8/11/08 at 10:40 PM |
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Hi all
Just realised that indeed I didn't open the throttles so all may not be lost as my readings were so low the engine shouldn't be running
very well ....stuuupid boy ....I even read the instructions and got it wrong  I'll praps give it another go tommorow and report back .
The car sounds so sharp I was gutted that something was wrong . I did try the oil down the plug hole test and it didn't much improve ....which
you rightly say is a good sign.
What a pillock ....and so pleased I am
"If it looks like it works and it feels like it works, then it works"
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NS Dev
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| posted on 9/11/08 at 10:53 AM |
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you are probably worrying too much.
if the bores looked ok and the bore to piston clearance was ok then it almost certainly will be ok.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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britishtrident
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| posted on 9/11/08 at 03:48 PM |
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With new rings you need the bores to have a pretty rough surface texture or the piston rings will never bed in --- I see nothing wrong with the way
you prapared te bores..
A few thoughts
If the 100 psi is roughly equal across all cylinders it says to me this isn't any thing major wrong with how you fitted the rings.
(1) are you doing the compression test with the engine warm, all the plugs removed and the throttle held full open ?
(2) Are the valve clearances OK -- ie are the valves closing fully and sealing.
(3) Valve timing --- ? it would have to be quite far out.
A wild cam can also have a serious effect on compression tes pressure but not as much as a 100 psi drop.
I would sugest if nothing is obvious doing a cylinder leak down test --- you will find DIY instruction on how to maker a simple leak down tester out
on the web or you can buy them off ebay.
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Valtra
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 posted on 9/11/08 at 06:11 PM |
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Hi all tested this afternoon
fully warm and throttles fully open this time
results
no1 177psi
no2 185
no3 185
no4 173
no5 happy bunny. car running better all the time. soon be time for high rev blast !
I even got my recently sick 500 running sweet as a nut , the LT lead from the coil to the points was earthing on the dizzy body. double result !!!
thanks for all your comments
"If it looks like it works and it feels like it works, then it works"
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