compression worry

PostPost by: phatmendus » Wed Oct 12, 2005 8:28 pm

Hi, Can someone give me some advise (hopefully goodnews)

After buying my elan I am now running/tuning it after about 12 years of it sitting around doing very little.

I have done a compression test on each of the cylinders, with the first 3 coming in at around 140 psi (10 bar ish) however cylinder 4 came up as about 110psi (8 and a bit bar). Also the plug in this cylinder is slightly oily when taken out, (although not too bad) The last point to make is that by shining a torch down the spark plug hole, the piston crown is VERY coked up and dirty.

The questions are: Is the compression of cylinder 4 at 110 psi something serious to worry about as it is around 30 psi lower than the others? If it is something to worry about do I need to do something about it now and also will it effect the running of the engine?

Lastly is the oliyness of this cylinder related to the low cylinder pressure (piston ring gone perhaps?)

One more point is that there is slightly blueish oily smoke out of the exhuast whilst revving it, I thought this normal on a TC engine but now Im worried! Oh yeh, the engine has done about 27k mile since rebuild.

Any advice?

Thanks

Simon
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PostPost by: 1964 S1 » Thu Oct 13, 2005 2:48 am

Hello Simon, I'll guess cracked piston ring at the worst and carb prob at the best. Do you have Webers? A Lotus sitting still for years ???? Can you drive it 75 mph down the road and if yes does it smoke at that speed?
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PostPost by: triumphelan » Thu Oct 13, 2005 6:41 am

Hi
I have a 1969S4 with Webers. On start up there is a little smoke ,no smoke at normal running BUT on a blast I leave a black cloud.
Regards John 1969S4DHC
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PostPost by: types26/36 » Thu Oct 13, 2005 7:47 am

[quote=s) Is the compression of cylinder 4 at 110 psi something serious to worry about as it is around 30 psi lower than the others? If it is something to worry about do I need to do something about it now and also will it effect the running of the engine?Simon[/quote]

As the engine has not been used for a number of years I would just use it for a couple of thousand miles, I have seen engines that have also smoked and with had uneven compression improve with use. I doubt anything dramatic will happen with use, if it gets worse then an engine rebuild may be reguired in the future but dont be in a hurry to pull it apart.
Just change the oil and fill it with a stright SAE 40 grade (you can use a multi-grade at a later stage)
Check the compressions again later and monitor the oil consumption, if it has to be rebuilt you may find there is other work that can be done at the same time.
Brian
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PostPost by: phatmendus » Thu Oct 13, 2005 8:17 am

thanks for the info everybody. Brian that is the kind of thing I wanted to hear! I shall leave it for a while and see how things go.

To answer the other questions. I finally had some success at tuning the carbs last nght. (they are delorttos) So in theory I could drive it a 75mph now as it seems to be running alot smoother, however I need to get some decent tyres before I attempt that as the original ones are falling apart!

The smoke issue really isnt that bad, and didnt concern me until I found out what the compression in 4 was.

On a last (and strange note) I posted a question a while ago about my headlight pods dropping REALLY slowly, it was a mystery. Anyhow after turing up the carbs to the best of my abiltity, not only does the car run better, but the headlights work exactly how they should! strange!

oh yeh, the reason why the lotus sat still for years was not because of me but due to previous owners who didnt have time,money etc to rebuild the body of the car, although the engine has been complete but not running since 1992.
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PostPost by: ppnelan » Thu Oct 13, 2005 8:36 am

Simon,

You could leave a little Redex to 'soak in' to the low compression cylinder. If it was a sticking piston ring, this should help.

If your headlamp vacuum system suddenly started to work properly, maybe it's a leak in a cracked pipe. I had a perished rubber hose connecting to the one-way valve on the manifold which leaked if it was moved around.
The one-way valve itself can get dirt in it which makes it leak - do your headlights stay down for long after the engine is switched off (I assume they are fail-safe type) ? Also, check for the original very cheap & nasty plastic T-piece on the front of the chassis vacuum tank - they go brittle & crack, leaking excess air into the manifold....

Best wishes,
Matthew
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PostPost by: phatmendus » Thu Oct 13, 2005 10:04 am

Hi Mathew,


My car is not the fail safe type it is the type that drop when you loose vacuum. It was a stange phenomonon as, before I played around with the carbs the headlights would pop up but a bit slowly really, then if i pushed the lights switch back in they would take litterally about 4 mins to drop, and when they did they went very slowly suggesting the vacuum was not be openned up to atmosphere when switched of.

When I tuned up the carbs last night I touched nothing else, and after doing so the lights went up much faster and drop down actively with the assistance of the spring loading. VERY ODD! I can only assume that my carbs were so far out of tune, that the butterflys were stuck open at idle, thus little vacumm build up in the manifold, but thats just a guess.

My worry is the compression, as to me even 140 psi (10 bar) on the 3 'good cylinders' seems low on a high compression engine (10.3:1), and frankly the 80 psi on the 4th really worrys me on an engine that is supposed to be on 25k since rebuild!

If anyone else knows there cylinder pressures using a standard compression tester etc, I would love to know.

Simon
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PostPost by: john-c-elan+2 » Thu Oct 13, 2005 11:35 am

Hi, the compressions on my engine (rebuilt big valver) are all between 160/180 psi. Don't forget to have the carb butterflys fully open when you take it ! The other possibility re no 4 low reading on your car, wud be a sticking valve or burnt valve/seat ? As Brian says change oil & filter and if its the valve sticking, a little use may free that up too. Good luck. jc
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PostPost by: theelanman » Thu Oct 13, 2005 1:21 pm

mine on the std twink were at about 130psi when it was running fine.......then it started runneing a bit rough....had it tunned....was only slightly better.......mine had coked up the plug on number 4 a bit too!!! thought it might have been a burnt valve or something....anyway head off...all ok.....looked down into number 4 cyl in the block to see a hairline groove in the cylinder wall!!!....doh!!!
havent done anything with it yet but as I have a second engine I'll be putting my head and block on ebay separately.....I dont have the time or mechanical inclination to bore and line a cylinder.....or to bore them all and go for +40 pistons or similar!!!
hope yours isnt the same........
cheers
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PostPost by: phatmendus » Thu Oct 13, 2005 1:39 pm

I HOPE NOT TO!

Simon
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PostPost by: elansprint » Thu Oct 13, 2005 5:23 pm

Simon do as brian says & give it a run for a while it may improve with use. My sprint was bought after a long period of inactivity & while compression was not as bad as yours it improved with running. When i converted to 5 speed i did the head etc & found the top ring on three cylinders broken into 3 pieces & was amazed to find the bores not scored. I think the rings must have been stuck & when previos owner got it started to dispose of it this caused the problem. Hope it is just inactivity in your case

regards

Ian
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PostPost by: stuartgb100 » Thu Oct 13, 2005 6:36 pm

Simon,

IMHO, you may/may not have cause for concern.
Your concern is not proven yet..... so persevere, but with caution.
Treat it as if you are running it in, having spent donkeys hours worth of
time/money on it. With luck ......

Suggest you change that oil and filter (and prime filter first!!)
Filter the used oil, and inspect!
Slowly, as useage/mileage increases, increase the revs.

Again a personal opinion:

Those compression figures seem generally to be low at that mileage, and obviously No. 4 is low. Perceived wisdom would suggest figures should be in excess of 160psi (hot) for a standard, or +170psi for a big-valve (hot) engine. All cylinders within a 20 psi range.

Personally, would not use Redex-type additives (at this stage).

FWIW ....... HTH.

Regards,

Stuart.


At worst you will only confirm fears.
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PostPost by: M100 » Thu Oct 13, 2005 9:52 pm

Without pulling the head the only way you can be sure is to get an endoscope down there and have a look if there is any damage to the bores, valves or piston. With ring damage the only thing that is going to isolate the problem is a leakdown test.

If you carry on running it could all end in tears. What might now be just a set of rings on one bore (20 quid) could turn into a rebore or resleeve (?????)

I'd check with another compression tester first though!
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PostPost by: bill308 » Thu Oct 13, 2005 10:30 pm

Of course the other trick is to ensure the engine is warm prior to taking the compression readings. In addition to ensuring the throttles are blocked open for the compression test, I remove all the plugs to ease the load on the starter when taking the pressure readings. After you take a reading on a cylinder, take a second one with a little engine oil squirted or fogged into the bore. The oil should help seal the rings. If the compression reading goes up significantly with oil in the bore, you likely have a ring problem. If it only goes up a little, then the problem is likely with the valve seats.

Bill
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PostPost by: 1964 S1 » Fri Oct 14, 2005 1:11 am

I'm with Brian and Ian, and others, oil change, drive it. No high revs, one day it may cough and be fine for years. Here in the states even Buick LeSabres coke up if not used for only four months.
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