Hi all, Over the winter I rebuilt my CJ 2L Type 4 motor - the story is in this thread (and continued thanks to everyone who contributed their advice); https://thelatebay.com/index.php?threads/fixing-what’s-not-broke….97558/ In brief; new P&Bs, standard cam, lifters, valves, bearings, re-ground crank, rebushed rods, lots of other smaller bits. CR upped to about 7.8:1. Running 20W50 oil. Now it’s back together, cam break-in done, oil changes done and run about 300 miles. Pulls very nicely, cruises happily - all better than before the build, except; There’s a knocking noise at idle. It sounds like a diesel, a lowish frequency, slightly erratic knock that disappears as soon as the revs are raised. If I rev the engine up and then turn it off on the ignition switch, then as the engine slows to a stop the noise appears as it slows through the idle speed rev band - so I don’t think it’s combustion related. It’s hard to pin-point exactly where the noise is originating from - have a listen; I’ve done all the obvious stuff; triple checked the timing, rebalanced the carbs, valve clearances, checked the fan clearance at all points against the housing. I've got to theories left of what it can be - cam related or oil pressure related. But I'd love to hear the thoughts from the regular Type 4 experts before I start stripping the engine again!
I'll go for fan hub isn't tight enough. If you can get a rattle gun in there. Pure guess but reminds me of one I had in the workshop to chase similar. The knock does sound hollow like the fan housing on the video. You could take the fan off and run for a minute to see.
Your fan is not quite straight.. it shows in the video. It sounds bright and "outside" rather than "dull" and inside the engine- like tapping on a tin can to me. Could be wobbly fan making fan belt hit something.
The belt isn't hitting anything and the fan is straighter than mine. I doubt if it's fan related but it's easy to check that it's tight. Is the noise with a cold or hot engine? If it's cold it might be piston slap; what material are the pistons and what skirt clearance do they have and do they have offset pins? Are the big end bearing clearances within spec? It could be excessive cam float but it sounds a bit too heavy for that. Follower or cam base circle wear would show up with a clearance check. Low oil pressure would show on the gauge, assuming you have one. And if you don't you could fit a temporary one instead of the switch. I've just noticed the thermostat is extended so the engine is hot. Piston slap is unlikely but it could be the cam knocking back and forwards – the noise sounds low down at the back of the engine to me. Back as in back of the bus.
Heh-heh, we'll see. I also tried everything else, the fan looked fine too, it was the last thing I thought of - there isn't a lot of clearance between the fan and the housing so it doesn't have to be loose, just not tight enough and it makes the bottom end noise, perhaps not the noise you'd expect. I could not locate it with my stick-o-scope or a hose-a-scope.
Thanks for those replies guys. I am unsettled by the fan and its wobble - the thread in the end if the crank isn’t great but it is all tightened up to spec. I put tell-tale paint marks on so I can tell that the middle nut hasn’t moved nor the fan against the hub. And, having taken the pulley wheel off I was pretty meticulous about putting it back on right; But it’s an easy check so I will whip it off next week. Geoff - yes it was hot, I’m a bit pushed for time right now but will answer everything when I get a mo! Bog standard AA pistons, dished so yes, offset. I think!
Just to finish off: The P&Bs are the AA set bought from Heritage. Ali pistons. So I didn’t measure the clearances, just did the rings and popped them in. The crank grind was spot on on all the journals - whilst I measured the mains clearances (which were also spot on) I’m afraid I didn’t measure the clearance on the big ends. I don’t have an oil pressure gauge! Measuring the pressure is a good idea for piece of mind if nothing else, so I’ll see if I can find a temporary one to screw in. One of my theories is the pressure control valve piston (which is new) is stuck open allowing big end or mains knock at low revs, then the pressure catches up with itself as the revs rise. But my real fear is that cam is flapping about. I can’t see how though- the drive wheel was on tight; can’t see how it could have come loose immediately on start up. Similarly I can’t understand where end-float would have come from - but I’ve got a feeling I’ll be taking it all apart to find out. Will report back with initial findings.
This bearing wear took a few years and the cam made a knocking noise very similar to what yours does.
Seriously, before you strip down your engine, rattle gun the centre hub nut, forget the spec, do it tighter. What do you have to lose?
Well I’d be all squeaky-bum about stripping the threads in the end of the crankshaft! I was mighty relieved when I got the screw up to torque when I put it together. As a matter of interest, how easy is it to drill and re-tap for a bigger thread if it all goes TU? I think the older fans had a bigger screw anyway…
It's only an 8mm thread, 23ft/lb torque, some (Porsche?) hubs had a cone centre but the thread in the crank is the same size. If the hub is loose on the taper with 23ft/lb it will still be loose at 33ft/lb and probably very loose at 43ft/lb. You could drill and tap the crank for a larger thread, but there is no need unless the thread is already damaged.
Standard AA cylinders are cast iron and the pistons are cast aluminium alloy, probably with about 9 or 10% silicon, nothing special but perfectly fine for a standard engine. However, AA quality can be suspect and the cylinders should have been checked for taper and/or barrelled bore and the pistons diameter and skirt clearance should have been measured. If you used Silverline big end bearings the sizes can be erratic, and of course the clearance should have been checked regardless of the bearing manufacturer. Incidentally, the noise is not a main bearing. Mains rumble, big ends knock. How much clearance did you have between the cam bolts and the oil pump? Why did you have to replace the oil pressure control valve? And do you mean the valve between the pushrod tubes or the one at the back? Back as in back of the bus.
[QUOTE="mcswiggs, post: 1984737, member: " .... the thread in the end if the crank isn’t great " [/QUOTE] @77 Westy, Geoff, not wishing to speak for @mcswiggs, but I think the mention in a previous post is why Dom mentioned rethreading as the current thread is partially knackered.
@77 Westy, Geoff, not wishing to speak for @mcswiggs, but I think the mention in a previous post is why Dom mentioned rethreading as the current thread is partially knackered.[/QUOTE] Maybe the thread was damaged by overtightening at some point, possibly due to a hub taper problem? I can't think of a reason why the crank couldn't be drilled and tapped to 10mm if necessary.
Seems like maybe you should have dealt with it at that point. On the other hand this is just a guess for your noise from video on the internet so maybe more tracking down of the cause would be better i.e. you can easily check if it's fan related simply by removing the fan and running it for a minute? Then if it is you can worry about stripping/repairing threads, if not you won't have hurt anything.
Agreed- it’s a simple test and I’ll do it next week - just need to take the fan off, not the hub and run it up. Also the oil pressure test too. I replaced the oil pressure control valve piston because the original was a little scuffed - not badly but thought it was a reasonable (and reasonably cheap) thing to do. There was something odd with the crank/hub when I took it apart - the space was filled with a kind of red powder that looks like rust, perhaps red loctite that had been pulverised. And the woodruff seemed to be missing (or I instantly lost it) - but it didn’t look like the fan had been spinning on the crank.
Fan does look iffy .. I used to get a knock sound and it was the fan hitting the plastic timing scale . ( replaced with metal ) Or pushrod tube retaining wire on pushrod ?
An idea... That fine brown stuff is probably pulverised metal from things spinning because of no Woodruff key.. it was locked together when you found it because rust is 3 times larger in volume than the iron it came from. It's also an abrasive.. think jewellers rouge.. it was probably OK until you took it apart and cleaned it, then there is now a gap where the metal was. It looks similar to what you get when you burn out a wheel bearing... If that's the case you need to build it up (spray welding and turning it down again) or wrap a shim round it to fill the gap.. and use a Woodruff key.. maybe glue on a sleeve then carefully cut it for the key.. A bit of a coke can.. or sacrifice a feeler gauge as a cheap source of selected calibrated shim metal..
