Motor Mystery...

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Spacenut
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Motor Mystery...

Post by Spacenut »

The Nova has been increasingly difficult to start when I head off for my weekly grocery trip, so I decided to investigate. I suspected fouled plugs, but after removing them all (NGK B7ES) I found nothing much wrong with them - gaps are all 0.75mm (NGK recommend 0.8mm), no soot or other contamination. The rear cylinder on each bank (3 & 4) catch a lot of muck from the rear wheel arch, which has led to some corrosion on the outer body, but after a clean-up they were good to go again.

So I ran a compression test on each cylinder, and the results did not look promising:

Cylinder Reading #1 Reading #2
1 145 psi 148 psi
2 105 psi 100 psi
3 125 psi 132 psi
4 130 psi 140 psi

The LH cylinder bank is the one that I couldn't successfully tune up when I rebuilt the carbs. Anyway, I poured a little oil down the plug hole of #2, and repeated the compression test - 200+ psi.

According to the books, this means I have a broken piston ring on #2, but I wondered if there was another explanation? Once started, the engine runs fine, although it has a tendency to fluff a bit when accelerating from low rpm, I assumed that was down to carbs or possibly my somewhat insensitive hydraulic throttle.

No smoke from the exhaust (the oil that I put down #2 burned away within a couple of minutes).

No coolant loss, no oil film.

There is a bit of mayonnaise around the oil filler neck, but I put that down to condensation.

The LH bank has had a replacement head gasket as the cam carrier gasket leaked badly on that side. I did remember to re-torque after a few miles of driving, as per recommendation. It is clearly not blowing between #2 and #4.

Thoughts anyone?

Lauren

alfadave
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Re: Motor Mystery...

Post by alfadave »

What mileage has the engine done?

Did you hold the throttle open when doing the comp test?

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

Hi Dave - the engine has actually only done 25,000 miles from new. It was a service replacement engine, and was confirmed as never been run when I bought it, although weirdly one of the inlet valves was cracked and had to be replaced.

Yes, wide open throttle when testing.

I can't believe how well it runs with only three-and-a-half cylinders, but even if you assume the absolute accuracy of my Brand X compression gauge is not great, you can't argue with the consistently low result coming from #2... I am fearing the worst :cry:

Gary Orchard
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Re: Motor Mystery...

Post by Gary Orchard »

A cylinder leakage test would be worthwhile if you have access to a gauge & compressed air supply.
That will prove if it's rings or valves

Sud 145
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Re: Motor Mystery...

Post by Sud 145 »

Hi Lauren, I had a low comp' reading on one cylinder prior to my engine rebuild and that turned out to be a snapped ring. My Indie said he'd never seen one before - luckily no damage to the bore.

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

Sud 145 wrote:
Mon Apr 12, 2021 8:18 pm
Hi Lauren, I had a low comp' reading on one cylinder prior to my engine rebuild and that turned out to be a snapped ring. My Indie said he'd never seen one before - luckily no damage to the bore.
That was lucky - I have had broken ring before on another engine which scored the cylinder wall. If it had been anything more exotic than a Vauxhall 1057cc it would have been curtains, as it was I got another couple of years out of re-ringing the piston...

But a busted ring seems like the most likely explanation to me too :(

Thanks Gary for suggesting a leak-down test. Not a facility available to me, sadly. In the current situation I can't really afford to be without wheels, so I might bring forward my plans to get the Alfatune engine commissioned. The current engine was only ever a placeholder, although it would be a shame to damage it beyond repair. Plus the Alfatune needs a Trofeo sump to fit around my gear linkage, and an ignition only ECU plus a rolling road map, none of which is straightforward :?

I still can't get over it though - I still get 28-32 mpg on short local runs, 40+ on longer journeys, oil consumption is virtually nil (unheard of in one of my cars), enough ooomph to get me to naughty speeds when joining the A3, happily revs out at 5,000 rpm... it's a mystery all right.

Lauren

alfadave
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Re: Motor Mystery...

Post by alfadave »

I did wonder if there was a DIY version of a cylinder leakage test available to those of us home mechanics? Get compressed air into a cylinder using a 12v compressor?

I would whip the head off and check valves/springs/head gasket. Lap the valves back in, and check the head is flat. Then it would be fairly quick to drop the sump and take no 2 piston/rod out, and check the rings. Fit a genuine new head gasket. Not a massive outlay of time and money.

Get Tesco to deliver in the meantime!

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Re: Motor Mystery...

Post by LooLooSud33Spider »

I didn’t know Tesco delivered Alfa head gaskets and piston rings ?? Good to know
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alfadave
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Re: Motor Mystery...

Post by alfadave »

Brisket with onion rings

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Re: Motor Mystery...

Post by LooLooSud33Spider »

That make sense now Dave. Does the Head gasket hold torque ok when using the bovine head gasket material ?? I’ve used lamb in the past and it Works well and smells lovely. But you have to remember to add mint sauce to your coolant !! Never tried piston onion rings before as the lesser known Calamari ring mod (Theyre tougher) has served me well over the years as an emergency “ get yer home” fix. As for emergency gaskets I find under done lasagne sheets work well .
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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

Hmm - thanks for those suggestions :?

It really is amazing how quickly you become reliant on motorised transport - I was without a car for 7 years while I redesigned the dashboard, wiring, swapped out the gearbox and rebuilt the suspension (and brakes!), now I am all in a tizz over losing the car for week or two. What kind of lightweight am I???

Lauren

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Re: Motor Mystery...

Post by junior »

That's the Covid experience for you, I had three tasks to do monday as i got out and made a mistake on each one.

Just not in the right frame of mind at the moment.

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

OK, thanks for the suggestions - lasagne, calamari etc. Very helpful :roll:

So I have noticed no change in performance before or since the compression test. Fuel consumption is the same. Oil consumption virtually nil. No excessive smoke from the exhaust. So I have concluded that I must have been living with this for years, and that got me thinking - I have only had the chokes connected for the last couple of years, prior to that I had to pump the accelerator to prime the carbs and it would always take a while to catch, particularly on a cold morning. Also, the reason why I rebuilt the carbs 2 years ago was because they were prone to float chamber flooding... I think I must have been over-fuelling the engine, leading to bore-washing. Leads to excessive piston and bore wear if allowed to continue.

As confirmation of this can only be obtained from a full engine stripdown, and may require re-bore/oversize pistons etc. to fix, I am advancing my plans to swap in the Alfatune engine, but before I can do this I need to resolve a clearance problem between the LH camshaft belt and the water pump (due to the amount of metal that has been shaved off the block and cylinder heads) - the belt runs too close to the water pump casting.

I have noticed that the 16v boxer engines run their cam belts very tightly around the water pump, and some units that I have found online appear to have no reinforcing webs and a solid cylindrical shaft housing.

Is there any difference between the original 8v pump and the 16v unit? If there is, and the latter has a narrower body, I could be saved, as there appears to be no other appreciable difference between the two.

Sensible answers please!

Lauren

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Re: Motor Mystery...

Post by Veesix75 »

Before you do any major changes, is it just me that is questioning why no smoke or oil usage if you have bore wear ?

When I had a broken bottom ring on one bore, it blew oil into the catch tank / breather so used it, it was down on power.

Are you doing enough miles to notice oil usage ?

One of the qualified engineers on here can correct me as I’m not one but I’d honestly expect power loss, burning oil or oil usage if you have bore wear.

Also, if the fuel wash was enough, then white smoke from over fueling out of the exhaust ? Contaminated oil ?

How many tests did you do, and can you borrow another compression tester to compare.

alfadave
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Re: Motor Mystery...

Post by alfadave »

A competent garage could carry out a cylinder leakage test on no2 .

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

Veesix75 wrote:
Sun Apr 18, 2021 7:45 am
Before you do any major changes, is it just me that is questioning why no smoke or oil usage if you have bore wear ?

When I had a broken bottom ring on one bore, it blew oil into the catch tank / breather so used it, it was down on power.

Are you doing enough miles to notice oil usage ?

One of the qualified engineers on here can correct me as I’m not one but I’d honestly expect power loss, burning oil or oil usage if you have bore wear.

Also, if the fuel wash was enough, then white smoke from over fueling out of the exhaust ? Contaminated oil ?

How many tests did you do, and can you borrow another compression tester to compare.
Hmm. All very good points. Perhaps it is down to valves after all. I know one of the clearances is out, I can hear it ticking. I didn't think that valve clearances could result in such a massive drop in compression pressure though.

Obviously with the lockdown my mileage has reduced - but I haven't had to top up the oil for the last 3 months, and I have covered maybe 200 miles in that time.

I did a repeat test on each cylinder, which you can see from above are reasonably consistent. The relative difference between #2 and the rest appears to be real if nothing else :(

I will continue my investigations. Forget about the 16v water pump by the way, I've had a good look at the Alfatune today and it won't work. However, a fabricated idler pulley extended by 12mm should do the trick. More news as it happens...

Lauren

Veesix75
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Re: Motor Mystery...

Post by Veesix75 »

Valve not seating, closing, bent should cause quite a compression drop surely ? Even the slightest leak is going to reduce pressure.

Hope you find it and it’s not too drastic.

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

Veesix75 wrote:
Sun Apr 18, 2021 2:55 pm
Valve not seating, closing, bent should cause quite a compression drop surely ? Even the slightest leak is going to reduce pressure.

Hope you find it and it’s not too drastic.
Thanks V6 - I hope that you are right.

rsfruitbat
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Re: Motor Mystery...

Post by rsfruitbat »

Many yrs ago I over revved an engine and a afterwards had lots of issues on tickover. Normal running no problems of when competing. Eventually got fed up and took the head off. What had happened was a valve had touched a piston and very very slightly bent it. The lower the revs the worse the leakage. Higher re vs and more acceleration into the valve seatby the valve would cause the valve to seat correctly and run clean.
All the best Lauren

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

rsfruitbat wrote:
Mon Apr 19, 2021 8:10 pm
Many yrs ago I over revved an engine and a afterwards had lots of issues on tickover. Normal running no problems of when competing. Eventually got fed up and took the head off. What had happened was a valve had touched a piston and very very slightly bent it. The lower the revs the worse the leakage. Higher re vs and more acceleration into the valve seatby the valve would cause the valve to seat correctly and run clean.
All the best Lauren

Rsfruitbat
Thanks Fruity, that's really interesting - and a little worrying too, seeing as I have been steadily extending the rev range to 5,000 rpm or more, now that I have a working tachometer. Perhaps I might have gone too far? Either that or the valve isn't seating properly, which is also possible given the noisy tappet. I will continue my investigations in parallel with preparing the Alfatune, although I am quite excited about the latter - it has a 1700 stroker crank in a 1500 block, lightened flywheel, skimmed heads and deck, 45 DRLA Dellortos, reprofiled cams and has a trigger wheel and TPS for a 3d mapped electronic ignition. It really is about as maxed-out as an 8v can get. It could be good for 150 bhp which is probably twice what I have right now 8-)

Lauren

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Re: Motor Mystery...

Post by rsfruitbat »

That sounds like good spec. I can definitely recommend mapped ignition and if you ever went down that route throttle bodies.
My old 1600 sounds similar and that had 96 at the wheels
5000 revs is nothing for a boxer. For a while I can a std bottom end. We would rev that to 7500 all day. My over revving scenario was 7500revs in second and went into first instead of third😧
Didn't like that.
You know what they say?
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Re: Motor Mystery...

Post by Mufasa »

Wise words Fruity
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alfadave
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Re: Motor Mystery...

Post by alfadave »

I'm interested to know if you have diagnosed your low compression problem on no2 ?

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

alfadave wrote:
Mon May 03, 2021 8:59 am
I'm interested to know if you have diagnosed your low compression problem on no2 ?
Not yet - but all the evidence points to a poorly seating valve at the moment. Reason being, I can detect no noticeable change in performance before or after the compression test, so my conclusion is that the problem has been there all along (since 2006, 25,000 miles ago). I had to have one of the inlet valves replaced before getting the car roadworthy because it was cracked. Replacement came from my tired 1978 1.5 Ti single carb engine, and may have been bent or otherwise not seated properly.

Using the car too much at the moment to take it off the road for further investigations, but the cambelts are due this Summer so I will continue investigations then.

Lauren

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

So I think I have finally solved the mystery of the low compression on the LH cylinder bank.

I checked the valve clearances as you know and found that the inlet and exhaust clearance on the LH bank were all too small by 0.05mm. I made up an adjustment tool as per your advice and readjusted all the valves on the LH bank. The valve clearance on the RH bank were measured and all valves were within specification.

So why was this? I believe the reason is because I have replaced the paper camshaft carrier gasket on the LH cylinder bank with one of those white plastic ones, without checking or adjusting the tappets afterwards. If the plastic gasket was 0.05mm thinner than the paper one this would explain the uniform change in valve clearance across all the tappets.

OK, so what about the cylinder compression? Having reset the tappets, I ran a compression test on #2 and #4 this morning, and can report that both are now back to the same levels as the other bank, around 146psi.

So it would seem that valve clearance was the only reason for the low compression on the LH cylinder bank.

But wait - there is more news! Because I stripped, cleaned and re-tuned my carburettors when the valve clearances were all wrong, I needed to re-tune them again, starting with a check of the ignition timing. This revealed that I had dialed in too much advance. Because I am a numpty.

I dialed in 8 degrees advance on my strobe light, and then adjusted the timing against the 8 degree mark on the flywheel :roll: This means I had 16 degrees BTDC!!! No wonder the engine was difficult to start :roll:

So, now the timing is fixed, on to the carbs, which had previously shown an imbalance between #2 and #4 that could not be adjusted out. This time #2 was showing signs of running lean (which I suppose is consistent with being tuned for a lower compression), so that was corrected, and a couple of turns on the #4 air bypass screw brought that cylinder into line with #2. My synchrometer now shows the same reading at idle for all 4 cylinders.

A quick run down the road suggests that all is now well again, the engine is noticeably smoother with fewer exhaust pops on the overrun, and no pops at all when at idle..

Thanks for your patience while waiting for me to complete this investigation!

Lauren

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Re: Motor Mystery...

Post by Kegsti66 »

Well done Lauren for persevering with the search.
Great to hear the problem was nothing too serious and your engine is now sound.
You should be able to enjoy your motoring green style again.

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Spacenut
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Re: Motor Mystery...

Post by Spacenut »

Kegsti66 wrote:
Sun Sep 05, 2021 7:49 pm
Well done Lauren for persevering with the search.
Great to hear the problem was nothing too serious and your engine is now sound.
You should be able to enjoy your motoring green style again.
Thanks Keith - yes, hopefully it will still be running well when I go to Brooklands next month for Auto Italia (ticket booked, and display car box ticked 8-) ). Looking forward to it, but will still keep a mask and hand sanitiser handy... and of course the weather in October can be a bit dodgy...

Lauren

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Re: Motor Mystery...

Post by KevJTD »

An excellent review of doing things in a methodical order and getting good results.
These are things that used to be commonplace to do on service whereas now it's little more than an oil change as the modern ECU sorts everything out. Even spark plugs often last for 60,000 miles!
Well done you for applying common sense and logic and being rewarded for it. And for getting tripped up on your fancy timing light, adjustable setting wheel indeed, stick to the basic one! :lol: Easily done, but at least your double checking methodical approach found it out 8-)
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Re: Motor Mystery...

Post by kammatic »

methodic and effective fault finding - good work 👍

alfadave
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Re: Motor Mystery...

Post by alfadave »

Good news and bad news really?

Four even compressions is good.
Under 150 psi , not so good?

Have you tried another compression tester, to confirm yours is ok?

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