Help! Oil leak and misfiring cylinder

[Ducky]

For the first time in 5 years of restoration I got my Datsun running! I'm over the moon but obviously there were going to be some issues.

Couple of things need advice on if anyone can help please!

Background info zfarm rebuilt my L28 engine, it was rebored to 2.85L with new pistons due to cylinder scoring, and had a carb specialist tune my rebuilt twin Hitachi SU carbs. Got l28 electric dizzy and electric fuel pump.

Issue 1 - Oil dripping from between bell housing of trans and engine. I've assumed it might be the crank seal.
I'm not losing a lot but it's continuous. There's also small wet patches around crank case at various points starting from the gasket. Appears more excessive at the rear which made me think maybe that's the source of the dripping.

Issue 2 - Idle cylinder one not firing. Under load get about 14.5:1 (o2 sensor fitted just after join of 6-1 exhaust) on average and all cylinders appearing firing well, it's just at idle and lambda reading goes to 16-17:1.
Using probe I can see spark on all cylinders but removing coils shows something is up with cylinder 1. Have swapped spark plugs and put new ones in and not a difference. Running twin Hitachi SU carbs so front 3 cylinders should be getting the same mix but but just not firing.
Carb specialist suggestion was to check the inlet and exhaust valves. I don't want to start taking the engine apart until I've made a clear plan.

Appreciate any help and feel free to ask for more info.

Thanks

Simon

 

[jonbills]

Assuming you paid for the work, you should just take it back and ask them to fix it, rather than getting into it yourself.
With the SUs, the only way for cyl1 to be different from 2 and 3 would be something inside the engine or the distributor lead or the distributor cap or the sparkplug.

 

[Ducky]

Yeah that was my first thought to try them. I've tried contacting zfarm and no reply ATM. I'll keep trying but do struggle to make contact with them.

Thought I'd try figuring it out if I don't hear from them or I can have an idea of what needs to be done.

Thanks for the feedback on the cylinder issue. Yeah I don't think it's air fuel mixture from the carb and spark seems to good. Leading to thinking it's in the engine. Again I'll keep trying zfarm and see.

Thanks again

 

[jonbills]

A couple of relatively easy checks would be to make sure the valve clearances are correct on cyl1 and the lash pads and wipe on the rocker are the same as the other cylinders.
And then a compression test....

 

[Farmer42]

So, I presume the engine runs with the other 5 cylinders but you get the misfire on that 1 cylinder. What is the state of the spark plug when you have run it for a few seconds. Is it wet, sooty or oily etc.? If it's wet, you are getting fuel and it's staying in the combustion chamber but the spark isn't igniting it. Its a bit like it's flooding. Sooty is the same but running rich which will eventually stop the spark. Oily and you have valve or piston ring issues.

The other thing to check is the post contact inside the dizzy cap. It could be worn with the result being a weak spark.

 

[Huw]

Assuming you paid for the work, you should just take it back and ask them to fix it, rather than getting into it yourself.
With the SUs, the only way for cyl1 to be different from 2 and 3 would be something inside the engine or the distributor lead or the distributor cap or the sparkplug.

Kind of agree with Jon. If you paid for the build, get them to fix it. As to the oil leak at the rear (if it’s engine oil), can be two things. The obvious choice being the rear crank seal or not so obvious, the oil seals for the rear main bearing. They are two rubber strips either side of the rear crank main bearing support, that are held in place by steel pins or ‘nails’. These will leak if not installed properly.

 

[Ducky]

Thanks for the replies and help.

I did manage to get hold of the guy that built the engine and arranging to take it back to him. Tbf to him he got back to me on holiday so I would appear to have been hasty in this instance.
Arranging new crank seal to be fitted and check everything else.

I still did a few checks over the weekend, as you guys said, and will share the cause of the problems once found if people want to know.

Weekend test results:
Compression test found no issues.
Spark plug from cylinder 1 is white, which aligns to the lean lambda reading.
Ran a spark tester and seems good so dizzy should be ok. I presume should see issues off idle as well if a dizzy problem, which I don't.

Again thank you for the fast replies. Until I can get it back in the engine rebuild shop in December I'll go back to rebuilding the wiring harnesses.