1923 Chief rebore ?

[Ken Lee]

Hello , does anyone know the maximum rebore that is safe on a blind bore 1923 Chief 74 inch please ??
Mine has nasty gudgeon pin lines that a previous rider ignored and kept running .
Many thanks and have a great Christmas and lotsa nice Rides in 2019 . Ken

[hairynob24]

G,day Ken these old barrels are very thin around base nut recess area . if I had my time over again I would have had them cylinder inserts around the 40 th size .and have a pistons made smaller to gain more life out of them , there is a company in the USA called Dinihanian Manufacturing who can build up the bore with Nikasil to 40 th ,this maybe something to look into ,they have an add in the amca mag page 15 … I think 60th is about the limit you can go . JD jugs here in Oz did talk about remaking them at one stage but nothing has come of it yet ,Rob

[Ken Lee]

Thanks Rob , yes would be nice to be able to get new cylinders , mine are standard bore and have been rebored 20 thou which still leaves gouge marks . I'll ask the firm doing the rebore if they can build up the bore with Nikasil , good idea . They say they do not think 40 thou will get rid of the marks and I don't really want to go much further , as you say , they are very thin cylinders ! Thanks , Ken

[Tom Wilcock]

I have taken early engines apart that had the pin grooves in the cylinders brazed up sometime in their past. They were obviously run many miles after with no apparent problems and the bores were still serviceable.
Tom

[Ken Lee]

Thanks Tom , I did ask about brazing them but they didn't want to in case of distortion !! but I will ask again and also about the Nikasil . Best wishes , Ken

[gharper]

Ken,

I ran my 24 chief with +.040" oversize pistons and .0065-.007" clearance on the last cannonball, dragging a sidecar. Never had any problems. I would be comfortable running them at =.050" oversize, but not more than that. The other thing I did was to cryogenically treat the cylinders and valve springs to relieve stress. It's a common process used on high stress engine parts.

The Nikasil process is a great way to go, if you can find a place that will do it on a blind cylinder. Shaky Jake here on the forum may have a source for that...... He mentioned it regarding Powerplus cylinders a while back on his powerplus or bust thread.

Sleeves are OK, but not ideal. If done, I like the idea of finishing the bore smaller, as opposed to boring way out and inserting a sleeve.

Gene

[Shaky Jake]

Ken,

I ran my 24 chief with +.040" oversize pistons and .0065-.007" clearance on the last cannonball, dragging a sidecar. Never had any problems. I would be comfortable running them at =.050" oversize, but not more than that. The other thing I did was to cryogenically treat the cylinders and valve springs to relieve stress. It's a common process used on high stress engine parts.

The Nikasil process is a great way to go, if you can find a place that will do it on a blind cylinder. Shaky Jake here on the forum may have a source for that...... He mentioned it regarding Powerplus cylinders a while back on his powerplus or bust thread.

Sleeves are OK, but not ideal. If done, I like the idea of finishing the bore smaller, as opposed to boring way out and inserting a sleeve.

Gene

I was surprised how well your Scout pulled that sidecar, Gene, especially in the end when you decided to turn it lose a little bit!

I ran sleeves in my Powerplus in this years Cannonball and they worked fine, but I hate the idea of removing any more metal than you have to from old original parts. I have a set of cylinders in my shop now that I had nikasil'd by U. S. Chrome in Fondulac, Wisconsin (I think they have their own name for the process, I can't remember at the moment). I haven't run them yet, but the bores are very pretty and are back to original size. The folks at U. S. Chrome were good to work with, you just get on their website and fill out a work order, and then ship the cylinders to them. They didn't have any problems with the blind bores.

Kevin


.

[Ken Lee]

Hello Gene , well done on the Cannonball and thanks for your comments . I have asked for .0045 clearance , would you advise .0065+ , using modern aluminium pistons ? I agree with the smaller bore if relining , I'll have a look for Shaky Jake's thread . Many thanks , Ken

[gharper]

Kevin and Ken,

Thanks for the kodos on the cannonball. Even though we had a magneto problem that made us loose a few miles one day, I'm still proud of the old girl for making the miles every day! The Indian Chief did well too!

Ken, I went with the looser clearance because I was forced to. My initial set up on the top end failed on the front cylinder within 50 miles, it scored the hell out of the bore! So, honed out until it cleaned up which was another +.012" or so. That put me at the .006-7" number. I honed the other cylinder to match as it was already +.040 over anyway. With a bit looser clearances, break in is much easier, plus my engine ran HOT, pulling a sidecar and 2 people plus all our gear, tools, extra gas etc. To split hairs, I'd go .005" minimum with cam ground aluminum pistons, but I would prefer .006". I just don't like fitting them close, piston or ring failure is catastrophic and destroys rare cylinder material. I think I could hear a bit of piston slap from time to time I think, but it was not excessive at all.

Kevin,

I planned all along to run about 45, that seemed to be the sweet spot. As you know, once you get out on the open road all alone and lots of others pass you up, there is a strong temptation to speed up a bit. I fought it for a while but gave in, and it was actually a good thing! If I hit hills of any size at 45 or less, it would bog down and with careful adjustment of the throttle and spark it would settle into a grind and pound its way up the hills, sometimes having to grab 2nd gear for a bit. I found that if I hit the hills at 48-49 mph, it would often hold that speed with less throttle, or even accelerate! To cruise on the flats at anything above 50 was very uncomfortable, it just seemed to fight itself and vibrated quite a bit. It was like a tug boat, it liked to pull hard, but not cruise fast so much!

I'm interested to hear how the nicka sil coating works for you. I've heard nothing but good things about it. It appears to be a good solution for damaged cylinders and is a better material, allowing use of modern oil rings with high tension and reduces friction quite a bit.

Gene

[Ken Lee]

Hello Gene , so glad the old girl did well (and the Chief) , I have a Princess sidecar to fit , had it on my 101 but is really too heavy for the poor old Scout hauling my old girl and camping gear !!
When I took my cylinders in I said give them .006 clearance but they persuaded me that .004 would be better as the modern pistons 'do not expand as much as the older ali ones' so we agered on .0045 but think after your experience I'll tell them to give .006 . and may have to go .040thou over pistons with '006 thou clearance and hope that will give a clean bore and as you say easier and quicker to break in , I'll also ask them about Nikasil to fill any marks . Hope you don't mind me asking all this but what gearing do you run ?
Many thanks , Ken