NC24 ENGINE REBUILD

[pagan1001]

Just so you know Neo I am an electrical engineer so I do know a fair bit so if you need to get technical then do.
But believe it when I say all your problems that you listed I have been through time and time again.
But I am not a novice by any means and I do understand what you are saying but I can assure you all these other things have been checked properly which really only leaves the engine its self to inspect other than a few wires I still need to test but will be finished this later on today.
But you have to agree if my oil pump has been blocked for god knows how long then I have to expect that at the worst the main bearings could be worn with excess heat and a lack of lubrication and that could just be the start of the damage.
I know you think these engines are bullet proof.......... and they are if looked after correctly but mine has not been in the slightest.

[CMSMJ1]

My tuppence would be that the main bearings either work or they knock and destroy themselves.

Air leak as mentioned by Neo for your revs problem..checked the rubbers etc?

I can sympathise with your wanting to take a motor to bits...but I'd get your "new" motor in first and make sure that doesn't have a knock or whatever the equivalent of owner hypochondria!

What was the oil strainer blocked with? Pieces of brass bearing? Bits of gunk?

Take lots of pics when you strip it, we like to see these bits and pieces!!

[Neosophist]

We can get really technical if you want to.

I don't mean to sound 'funny' with you, but ripping apart the block without knowing why you have these problems is akin to stabbing around in the dark.

Fair enough on the oil-starvation for checking the bearings... if they've gone they'd make an audiable rumbling.

Worn bores are the most likely culprit for running if everythign else is sorted, which like I said would write the block off (barrels are part of the cases) no over-sizing exists, you'll be lucky to get standard rings. A compression tester will help you with this.

But this doesn't really explain the erratic idling.

Where abouts are you located?

What settings are the following:

Float Heights
Main / Idle Jets (front and rear)
Emulsion tubes (how many holes)
Pilot Screw settings (do they all have the spring / washer / oring on them)

It's hard to diagnose over the internet but from what you've said, internal problems or not they don't sound internal.

I have a 1964 Suzi 50cc engine (Well I have 3 of them) that i'm rebuilding, it has worn big ends and rattles to fuckary but it still idles ok...

[pagan1001]

Yeah I know what your saying!
When I stripped the sump the gauze was blocked with .......... if you can imagine paper kitchen towels being soaked then ripped into tiny pieces it was like that. The best idea I had was if someone was working on the engine and had these towels covering various parts to stop contaminants getting in then forgot to take them out!!!.
Also in reading haynes it said you may find fibrous like material in the sump gauze which is due to the clutch being worn!?!?......... but I dont know about that one as there was loads of this stuff.
Today I am stripping the carbs again to recheck everything just incase I missed anything so will let you know. But I do have brand NEW rubbers on them so cant be an air leak there but will check elsewhere for worn rubber seals.
I finished the wiring and yeah it is okay not in amazing condition but okay for the time being I think sometime in the near future it will need replacing but I understand the loom is no longer available???? or is it????.
But all the jets are the correct size and the strainers (filters) are in good condition.
The carbs have been well looked after since I have had this bike, The one thing that I aint too sure about is the pilot screws as I have heard all different settings for these. In the book it says 2 turns but I have found that 2 1/4 turns is better and heard people saying 2 1/2 is the best so might test all these settings to see. If you know the best set up then let me know cheers for the help x

[Neosophist]

But I do have brand NEW rubbers on them so cant be an air leak there but will check elsewhere for worn rubber seals.

They still can leak if there not mounted properly, jubilee clips are over-tight or under-tight. I've had new ones leak before, took a couple of attempts to get them to seat on the engine properly. Fluctuating revs at idle is classic air-leak sign.

But all the jets are the correct size and the strainers (filters) are in good condition.

What Size jets are in there, what emulsion tubes do you have in the front / rear?

What are your float heights set to?

[pagan1001]

Yeah just finished checking the carbs and everything is bang on spec except the pilot screw but thats just the way I like it 2 1/4 turns out.
The rubbers are seated correctly made sure of it tried them a couple of times just to be sure and they are perfect!.
There aint anything wrong in there trust me. Took special care in checking it all!!!.
I did find one problem with the starter clutch the three nuts securing it were all loose so I have tightened them all to the right torque but thats been two or three times they have come loose now which they should not have, not in this amount of time or do you guys have this issue as well or is it just the way it is????.
I have quite a few bolts that come loose a bit to often so might add anti vibration washers to them all were I can. Have some of you done this already or do you just check them every so often???
Saying that though a lot of the frames threads are going with age so have been re - drilling them and fitting coils and most of the bolts have had to be replaced due to becoming rounded or showing signs of weakness and hate having them break off its the one thing I hate doing................. removing broken off bolts!!!! AAAAAARRRRRGGGGHHH!!!!!!
There is a guy on ebay selling titanium bolts any size and shape for next to nothing and they are fantastic for certain places like the pinch bolt holder and the gear lever bolt and other places that are problem areas!!!.
But Neo the carbs are fine, there is one filter that could do with replacing but cant find anyone selling new ones!?!?. Hope you can help with this.
Iam checking the starter motor now just to make sure as I was always a bit unsure of its reliability!!!!! If you can think of anything else I should check please let me know..... thanks so much guys you have been a real help xxx

[Neosophist]

What size jets are in there though? And which emulsion tubes do you have in which carbs (they are different!)
And what did you set the float heights too / how are you measuring them?

It's ok saying everythings ok but theres a lot of wrong information about, even in the haynes manual which will affect your running, especially at idle.

Pilot screws should be 2 turns out to start with and fine tune it from there, usually either half a turn each way.

Never had a problem with bolts comming loose in over 30,000kms of riding an NC24 unless I havn't tightened them up properly.

The bike in questions had the engine out, and all the bolts are original (i'm a stickler for standard things). I put threadlock only on the bolts that are supposed to have it on.

Sounds like the bolts have been over-tightened and it has stripped the threads out of the realativly soft aluminium. Another problem is when the bolts fuse into the aluminium, unless your very careful taking them out it's easy to round the bolt off and rip out the thread.

Be wary of using titanium / differnet bolts on mating surfaces, depending on whether a lubricant is used on the bolts or not they'll torque up differently. You'll either reach the required torque without achieving the required tension on the mating surface or conversly you'll achive torque with too much tension and crack / weaken the aluminium, which makes it quite easy to see why the 'torque' figure of TI bolts is such a hot topic.

It might be worthwhile tapping the holes to the next size up and replacing the bolts with larger ones, remember to take into account you won't need the same amount of torque on a larger bolt.

Soak everything in Plus Gas for a few days before you try to remove stubbon bolts and then rock them right to left slowly until they give.

[pagan1001]

Cheers for the info............ great will do all that you have said!!!.
Shit I hope haynes is right cause all my settings are by the book everything is set to their specs!!!.
Just noticed something when I washed her it sounded like water getting into the engine somewhere but it was very, very hard to notice or hear exactly where!!!. So Neo you may be right mate about an air leak somewhere.
I will need to strip everything off her again for a real close inspection!. I have been trying my best to look for possible leaks but cant see anything as yet so am going around her systematically......... hope I find the problem!!! I mean it could be anything a tiny crack a surface that is pitted or scored or a gasket away somewhere but both heads do have brand new gaskets but the ones on the carbs arent! or could that have been water getting under the spark plug boots???? As they dont look like they seal too well. I dont know just going to have to take my time on this one but if you can think of anything let me know as you are normally right. I just hope it is not something that is cracked or damaged will get back to you got loads to do cheers x

[Neosophist]

Right, theres a lot of contradicting info in this thread now.

ones on the carbs arent

Do you mean the float bowl gasket or the carb rubbers that join the carbs to the engine as I thought you said you'd replaced these?

The spark plugs won't matter.. water can't get in the engine from there unless you've not tightened the plugs up properly, theres drain holes in each plug too to let the water out too.

You only have to compression test it to see if you have a bad gasket. Your really making it hard work for youself by trying to guess and assume things.

I'm 99.9% sure it's carb / fuel related, i've seen many of these old engine with similar, if not identical problems.

Can I have some jet sizes please? I've asked numerous amounts of times but you havn't said and I can't help you to get it to run properly without the whole story.

As I said before, if you do all the following in this order you won't have any problems from the symptoms you've described.

1) Check and set valve clearances, these are the main source of engine noise and top-end rattle, they WILL also affect the running of the bike.

2) Strip, clean and rebuild the carbs, set the float heights and make sure the Jets and Emulsion tubes are in the right carbs and the pilot screws are re-set.

3) Replace the carb-rubbers, there probably shot and leaking.

4) Replace / Check the vaccumn hose from the fuel tank to the engine.. if this is leaking it wont run properly and you won't get proper fuel delivery.

5) Install the carbs and balance them. Check the balancing screws all have there aluminium washers on there and are all present.. otherwise you'll have another air-leak and more possible problems.

6) Fine tune the pilot screws

Seriously though all of this can be done in an afternoon, you can't skip a step either and they must be done in order.

Running it with such a bad air-leak and other symptoms is only going to kill the bike. Running an overly lean engine for an extended period of time will burn the valves out and ruin the engine.

If your still having problems give me the jet sizes, pilot screw settings, what emulsion tubes you have in which carb and float height level, along with what you've set your valve clearances to.

[pagan1001]

Yeah the gaskets around the float chamber are not new.
Right my pilot screws are turned out 2 1/4 turns, My float heights are 6.8mm measuring from where the gasket would be to the bottom of the float, my pilot jet is 35 and the main jet front is 112 and rear 110. I have not checked for emulsion tubes but will strip this sucker again tomorrow so will let you know on that one. I will go through it as in your steps and see. The fuel pipe from tank to engine is perfect.
So I will get back to you on this tomorrow.