NB8A lacking torque after recon head & new rings

DTH · Postby **DTH** » Thu Mar 01, 2018 3:46 pm

Hi guys, A couple of weeks ago I had my 140,000 km NB8A's head reconditioned (valve guides were bad) & new rings & conrod bearings fitted. I thought that with the head work & new rings the engine would now have a bit more power but it doesn't. The most obvious difference is the lack of torque on hills - less than before the recon. Had the spark plugs replaced today and the fuel filter checked. No difference.
I would appreciate any suggestions, thanks.
david

StanTheMan · Postby **StanTheMan** » Thu Mar 01, 2018 4:08 pm

valve guides bad at 140K ? sheeet :shock:

what went on there?

I'd check compression. report back.

check timing but if that's out 1 tooth....you'd really know about it.

dont forget it might take a bit of time to have the engine running freely if your bearing & cams went in a bit over tightened.

greenMachine · Postby **greenMachine** » Thu Mar 01, 2018 6:05 pm

Betting it's timing. Could be clogged air filter, blown head gasket, but my money is on timing.

:mrgreen:

Postby **NitroDann** » Thu Mar 01, 2018 7:12 pm

110%.

Thats my call too. Whether ignition or crank.

DTH · Postby **DTH** » Thu Mar 01, 2018 7:33 pm

Thanks for your suggestions, guys. I appreciate it. Cheers, david

DTH · Postby **DTH** » Fri Mar 02, 2018 9:59 am

Just spoke to my mechanic who did the above work. He said the ignition timing is not adjustable on this model NB8A. Is this correct?

greenMachine · Postby **greenMachine** » Fri Mar 02, 2018 10:34 am

Tell him to check the timing belt, that it is not a tooth (teeth?!) out on the cam pulleys. Also that the tensioner is working, dunno but that might affect timing.

A long shot, but BP engines can still have crank nose problems from hamfisted mechanicing. Worth checking physical TDC (ie screwdriver down plug hole) against timing marks to ensure the crank pulley hasn't moved. Did you (he) do the timing belt at the same time?

Same bloke DTH? Not sure that he has a great track record ... :frown:

RS2000 · Postby **RS2000** » Fri Mar 02, 2018 11:45 am

DTH wrote:Just spoke to my mechanic who did the above work. He said the ignition timing is not adjustable on this model NB8A. Is this correct?

That's correct (unless you do mods to the crank timing wheel). As others have said, check the crank/camshaft timing.
Also, probably worthwhile to check that the crank position sensor is not loose, & the air gap from it to the crank timing wheel projections is 0.5-1.5mm.

DTH · Postby **DTH** » Fri Mar 02, 2018 11:57 am

More good advice, thanks RS2000

93_Clubman · Postby **93_Clubman** » Sat Mar 03, 2018 10:24 am

Crikey David, you've had a very ordinary run with that NB8A - usually they're bullet proof except for one of the two ignition coils going in the coil pack.

DTH · Postby **DTH** » Sat Mar 03, 2018 5:44 pm

G'day Paul, yes, ordinary indeed. This one seems to disprove the bulletproof reputation. Still, I've been enjoying (somewhat) working on it as I'd given that up some 30 years ago. Things like this can be frustrating though. I haven't found the cause to the problem yet. Thanks for your interest.
Cheers,
david

manga_blue · Postby **manga_blue** » Sat Mar 03, 2018 7:04 pm

I don't like to be the bearer of bad news but I have to say that if simple matters like ignition or valve timing don't fix it then you may need to have an awkward conversation with your mechanic about his competence.

Two things could cause trouble: either the engine doesn't want to go or something is stopping it from going (or worse case - both)

The first probably comes from lack of compression. Maybe the rings haven't seated properly. What instructions did he give you for bedding in the rings and did you follow them? How worn were the pistons and bores before the work was done? Were the bores rehoned? How did he check piston fit against max tolerances before he refitted them? Otherwise the valves may not be seating properly, either because he's stuffed up setting clearances and some valves don't fully close or the seats/valves were cut incorrectly or he's damaged some. All these things can be uncovered with a compression test. Everybody should get this done anyway as a general test/certification of the work whenever they get a rebuild.

The second usually means something is binding. Either the rings were too large, so the ring gaps are too small, and these are binding in the bores. Or he has fitted bearings too tight for the journals. Or something funny has happened with positioning of crankshaft thrust washers. Or any number of minor things are wrong (cam or crank pulleys dragging, ancillaries, etc, etc). The rough test for binding is basically to rev it in neutral and see how fast it returns to idle. If it's a stupidly fast return then there's enough drag to affect performance noticeably, usually until something terminal happens. If that's inconclusive then you need to take all the plugs out and turn it by hand to feel the resistance.

Good luck.

greenMachine · Postby **greenMachine** » Sat Mar 03, 2018 9:36 pm

I missed the rings and bearings bit, just focussed on the head :oops:

.

What Manga said, and I would also DEFINITELY check that TDC on the No1 piston was TDC on the crank pulley timing mark (screwdriver down the plug hole).

I take it you have the car at home? Are you familiar with the timing marks on the cam sprockets, I think this is the most likely source of the problem and should be ruled out first, before looking at some of the other possibilities.

I hope you started with a full head of hair, if you didn't, there can't be much left now ...

Seriously, good luck, and keep us posted on developments. None of us like to see a fellow owner doing it tough, and if we can help from the sidelines are happy to do so.

:mrgreen:

DTH · Postby **DTH** » Sun Mar 04, 2018 6:59 pm

Thanks Manga and Ed for your suggestions. I appreciate your help. I've given some answers below to Manga's questions:
"What instructions did he give you for bedding in the rings and did you follow them?" I asked about that & he said that wasn't necessary.
"How worn were the pistons and bores before the work was done?" Not badly though the rings were gummed to the pistons & he said hone marks were still visible. Hmm, after 140,000 kms?
"Were the bores rehoned?" Yes.
"How did he check piston fit against max tolerances before he refitted them?" I don't know.
I've checked the ignition timing & it's OK. Currently in process of removing the cam cover to check cam sprocket timing marks. The ignition coil assy is proving obstinate tho' perhaps it's just my lack of knowledge. Suggestions welcome.
Cheers guys

RS2000 · Postby **RS2000** » Sun Mar 04, 2018 9:56 pm

DTH wrote:The ignition coil assy is proving obstinate tho' perhaps it's just my lack of knowledge. Suggestions welcome.
Cheers guys

On the NB8A there is a bolt centrally under the coils which attaches the coil pack bracket to the back of the engine. You might need a mirror & torch to find it!
However, you shouldn't need to remove the coil pack completely if you don't want to. Loosen that lower bolt, remove the top bolts & lay the coil pack back to allow the cam cover to be lifted off.