74" head cracking

[pisten-bully]

I've been getting my Chief ready for warmer weather, and one thing I do each off-season is to clean the carbon off the pistons and heads. This year I found a crack in the front head, first thinking it was a casting flaw. I had never noticed this before, but two years and 12,000 miles ago I had the front plug blow out of the hole during a ride, took the insert with it. I threaded it back in and got home, ordered a new insert and been riding it ever since, I even cleaned carbon off two times before I noticed this crack! Toyed with welding it up, but then I see it has cracked all the way through, and there are some other small cracks developing around the perimeter of the plug hole. I may have used this head for 12,000 miles or more with the crack, but I think it's time to replace it!

crack from the inside of the head:


...and barely visible on the topside:

[Lipdog]

Looks like it is time to replace it. In my experience, repairing things like this is a last resort if a decent replacement part is available.

Curious, why do you think it's necessary to pull the heads off to clean the carbon every season? I'm new to these bikes, but I hear of them going tens of thousands of miles without ever being taken apart, if maintained well. I also find it difficult to clean carbon off pistons without getting small pieces between the piston and the cylinder, likely scoring the cylinder walls. So I usually just leave it alone unless it absolutely needs to be taken apart.

[pisten-bully]

Curious, why do you think it's necessary to pull the heads off to clean the carbon every season?

I guess that’s a good question (says the guy tediously scraping carbon!) All I can say is I’ve never found a lack of carbon to deal with. My pattern has been 5,000 to 6,000 miles of summer riding, and in the winter I perform my “annual” (think that’s aircraft terminology) where stuff like wheel bearings, chain, etc. gets serviced. And I always take off the tanks, drain them, and blow them dry and they hang all winter from the rafters...so,with the tanks off, the heads come off. I’m often a “if it ain’t broke, don’t fix it” person, but if I’m going to use this motorcycle regularly, and depend on it, then I’d better take care of it.

[Peter Cooke]

All I can say is I’ve never found a lack of carbon to deal with.

Just wondering what brand of oil you use Harry? Some brands like Aeroshell are, supposedly, meant to reduce carbon build up quite a bit.

[Lipdog]

How do you avoid small pieces of carbon getting between the piston and cylinder wall?

[pisten-bully]

Just wondering what brand of oil you use Harry? Some brands like Aeroshell are, supposedly, meant to reduce carbon build up quite a bit.

Peter, I’ve been using VR1 50w. But I’ve heard Aeroshell is a good option (less or no ash?) I’d be interested in trying it (I need to order the VR1 anyway, it's not on the shelf anywhere around here).

Lipdog, I put a little grease around the top of the cylinder wall before bringing the piston up, and I also vacuum every few minutes.

[Peter Cooke]

Peter, I’ve been using VR1 50w. But I’ve heard Aeroshell is a good option (less or no ash?) I’d be interested in trying it (I need to order the VR1 anyway, it's not on the shelf anywhere around here).

It's been improved recently apparently. If you do try it I, and I'm sure others, would be interested to hear what you find.

https://www.shell.com/business-custo...-30071535.html

[stan]

Years ago someone told me about this method to remove stuff from the top ring and the cylinder wall. Bring piston on the down stroke about an inch. Pour some oil in on top of the piston. let it set until the oil has reached the top ring. Continue the piston down, you will see the crud the oil has picked up. Wipe the oil off so it doesn't go back down. stan

[PRG]

Howdy chaps,

Ever wonder why you can run modern vehicles 100k between plug changes? Engine mgmt enables these engines to run lean, clean and via real time ignition adjustment (in some cases on individual cylinders) efficiently across a broader rev range. This not only reduces deposits left behind but the amount of abrasive filth swirling around abrading running surfaces. As described in a previous post here I removed the heads on my hot rod 80ci 48 Chief in February for the first time since 1996 to replace the .032 inch fiber gaskets with .60 copper ones to reduce the compression ratio. Only a light brushing of the pistons and head surfaces was required. As flatties exhaust valves run much hotter than OHV motors that was the only surface requiring more aggressive cleaning, the residue more tan than black a reflection of the fuel used. As this motor has run clean you’ll note cross hatch marks still visible in the bores even though I had minimized my RA with a very fine final hone back then.

Assuming good oil control, the key is running leaner: more accurate fuel metering with a composite float, Crouch type electronic ignition and extended tip plugs. Most importantly no usage of set-and-forget ignition settings. Essentially ignition efficiency is only at idle on retard or at some point in the mid/upper rev ranges in advance depending on the distributor. Anything else is inviting incomplete combustion efficiency and resulting residue and deposits/wear. A Chief (or Knuckle for that matter) is a willing old mule totally reliant on its master to apply its power effectively. I’d encourage anyone to work on their advance linkage where it can be freed up like the throttle (most I found nearly bound up) to be used regularly to “feel” what the motor wants at any given rev range.

[Lipdog]

Assuming good oil control, the key is running leaner: more accurate fuel metering with a composite float, Crouch type electronic ignition and extended tip plugs. Most importantly no usage of set-and-forget ignition settings. Essentially ignition efficiency is only at idle on retard or at some point in the mid/upper rev ranges in advance depending on the distributor. Anything else is inviting incomplete combustion efficiency and resulting residue and deposits/wear... I’d encourage anyone to work on their advance linkage where it can be freed up like the throttle (most I found nearly bound up) to be used regularly to “feel” what the motor wants at any given rev range.

Peter, this is very cool info, thanks. I'm new to these bikes, having just purchased this rebuilt '48 Chief less than a year ago. I've only put a few hundred miles on it, as I'm trying to get it dialed in. As you mentioned, one of the things I did was go through both the throttle and advance cables/linkages, and they now work extremely smoothly and easily.

Generally the only time I use retard is when I start it. Otherwise I leave it at full advance. I get no pinging, and am thinking that engines are generally more efficient the more advanced you run them, as long as there's no detonation. When and why would you retard it once the bike is running and warm?

The other question I have is on carb adjustment and mixture. I went through the carb and replaced some parts, including Cotton's float, and adjusted it according to the manual and Kiwi Mike's method. It runs nicely but the plugs still look a bit rich and there is carbon inside the exhaust pipe. Were you able to adjust your bike so you don't have these things, and if so, what do you do?

[motor-officer]

I was recently on a Willy's Jeep forum. They were discussing old, barn type finds that had been sitting for many years.
The discussion was based on what steps should be taken before trying to start the engine.
One of the gentlemen mentioned that he used a product called "KREEN" in both the gas and oil to quickly remove
old internal carbon build-up. Kreen is made by Kano Industries, the same company that makes Kroil.
Wondering if anybody on this forum has used Kreen in their old motorcycles for this purpose?

[PRG]

Howdy sir,

Sorry for delayed response, new toy added to herd has been a distraction. Not to get into a discussion of pre-ignition/detonation - long topics - at a low 5.5/1 CR combustion stress will be limited to hotspots (glowing exhaust valves/carbon) and that rare, so you are unlikely to hear any rattling underway. Efficiency. If you were to remove a head and hit the piston with a soft mallet to mimic combustion in nearly all cases the most efficient range, ie, cylinder pressure generating torque, is between 15 to 18 degrees ATD to ensure maximum transfer of this energy into work. Too early, basically the rod is beating its big end against the crank pin like you hitting an anvil with a hammer rather than transferring the energy into rotation. Too late, piston farther down the bore resulting in more cylinder volume thus muting the violence of the expanding gases. Yes, in under square (stroke to bore) motors this less an issue as every millimeter of downward piston travel is not reducing cylinder pressure as much. Flat heads (and especially 38-42 Fours) have poor flame propogation, that’s why u see inconsistent carbon build up so thus the incentive to use your advance more often to ensure max burn leaving less residual deposits. Heat to a degree, ..pun intended, adds to efficiency, thus, on a cold motor with irregular fuel atomization and a cold cylinder enclosure you want less advance to ensure as much burn as possible.

I run Cotton type floats lower than the old recommendation for the heavy copper variety as they control fuel more accurately. Jerry Greer use to joke that the carb and machine bounced down the road while heavy unresponsive copper floats stood still blubbering uncontrolled fuel out the top vent. The carb fuel feed (nozzle) has a sort of built in accelerator pump. Lowering bowl fuel level reduces surge on cracking the throttle with its attending richness. Modern fuel formulations make plug reads difficult. Especially as a low compression flathead, you’re going to have carbon build up within your exhaust and your plugs may look a bit darker everywhere but the center electrode. An offline poster asked about plugs. I use extended tip NGK BPE7 or 6’s. Later 80 inch heads have full depth plug inserts, early do not, thus, I turn off a third or so of the plug threads on my 346 to prevent binding on removal from entrapped carbon. I can only think Indian ran short J6’s to prevent oil fouling like JC Whitney once offered in their catalogues with plug extenders tubes. Unfortunately, the trade off here is lost efficiency with the plug enshrouded. Extended tips expose the entire electrode to the combustion chamber. But, it requires a little more finesse by the operator on a cold motor started on choke as you have partially un aerated fuel splashing around which can cause fouling. Again, prudent use of ignition retard will clear it momentarily.

[motor-officer]

Does anyone know if this spark plug - "NGK BPE 7 extended tip spark plug" is still available. I have been unable to find any, including on the NGK website.
Has the nomenclature number changed or been dis-continued?
Thank you.

[indian301]

The only cross reference I can find is BP 7 ES.

Dave

[Fernleigh]

I would agree with others, time to replace. Murphy's Law suggests that when it finally goes it will go in a big way and perhaps do more damage. You should be able to find a decent replacement.