This has been bothering me since I found a crack at the base of one of my cylinders this winter, was not causing a problem, yet. We all know that the two cylinders lengthen when hot and the space between them grows. But if we tie the two together at the top with brackets that support the throttle body and horn, to me this would cause high stresses on the cyl to engine case because this expansion is being restricted, right? Wondering if there is a relationship here. See picture.

Replaced cyls and have bike back together, just trying to come up with ideasto prevent this from happening again. They were Nikasel cylinders which some say could be the problem, replaced with Axtell cyls. Because I am using S&S heads, had to make acustom bracket that connects to the two heads that holds the engine cooling fan. This bracket is very strong and non-flexable, wondering if there is a relationship between it and the crack.

[IMG]local://upfiles/21821/135F0EF867E74848AE219A5F5E3E396C.jpg[/IMG]

 

This is interesting. It is hard for me to see this real good. This is at the base right?? I don't think the throttle body would be much of a factor. Very interesting. Upper bracket?? I figure you are right about these expansion issues. There may be some problems but if the brackets bolt to the tops and are not straight across, a little bend to them they would have some give. Is that billet aluminum? Wouldexpand somea little and help I think.

Nikasil cylenders is used in Lycoming airplane engines with no problems. But there are differences with Harleys. Heat and stress. Nikasil is a coated all aluminumcylinder. Basic strength issues are more the problem not wear are more to the point for your engine.

My thoughts are based on the turbo and the stress put on the engine. The crack is down low. I would think at a relative unstressed area, normally. My thought is there is movement here. The engine thinks it is about 160-170 CID with this pressure. Maybe the upper limit for a stockcase strength if that is what it is. I think the stresswas trying to lift the cylinders under load. Moving themaround. Just not strong enough. Also cams and springs try to lift the heads off. Push things around some.

Fatigue crack is the word I am thinking about.

Are, did, you use very good cylinder studs?? Stock studs wouldn't get it done. I use SE On mine but with yours I woul have used Feuling or JIMS studs and head bolts. I know AXTELL fits a base gasket here, probably help this. And tightened a little bit more than the book. Maybe 45 Lbs. Ft. But if the case moves--???

The other thing is just strength. Axtell and Jims cylindersare much more robust that stock. Very heavy iron liners. Got to help.

I have no idea how you tune something likeyours but I know from mine that you can tune each cylinder as a seperate engine. This will cause the engine to try to tear itself apart if you get it wrong. So if each cylinder is tuneable may be something to look for.

Do you need 10#'s boost? Maybe 7# would do for a road bike. Drag racing's another story.

Thatssome thoughs. I am very interested to see what others have to say.

Must be interesting when you twist the trottle. Hot Dog!!!

 

Could be a case of things not level on the flanges, or just plain old piston slap.
Ron

 

I wonder if someone would have or know of --letting the engine get hot, maybe ride around a little to get all even, then lousen the top motor mounts, let them find their new position, maybe even let idle a few seconds.Then tighten back up hot. Hummmm--- a new though.

I doubt that. I am sure somebody thought of that no later than 1915. Glenn Curtiss for one. No dummies there.

If that was something that was helpful we all would be doing it today. Be in the book.

 

Apparantly tieing the two cylinders together with a metal strap is no problem which surprises me, the top engine mount connectswith a heavystrap bolted to each head. It would be interesting to know how much the cylinders grow in length from cold to hot, I know exhaust systems really grow, ever put solid brackets or strapson them and see things break?

Your question concerning cyl studs, I am using Fueling brand studs now with the new Axtell cylinders, not sure what the engine had in before with the Nikasel cylinders because I purchased bike off of Ebay. What the previous owner told me was in it for modsand what was actually in it were two different stories after tearing engine down to check that out.

Yes, twisting the throttle gives quite a ride, I was in the 160+ HP range with 10 psi boost, I have had some more head porting/polishing done at GMR and am hoping to stay in that HP range with less boostnow. I'm addicted to HP so once you've had it I can never be satisfied with less, you know. Thanks for your responses.

 

I think this will be fine with the new Axtell cylinders and fueling studs. Course you could always find a new weak spot. I think you will be fine with this now.

I know what you mean. This is a neat challenge, keeps the heart going.

My heads were done by Wolfgang Grousser. He knows a thing or two about horsepower and stress. Among other things has won several Horsepower Shootouts at Datona and other places last few years. He is listed on Woods site and also Eldelbrock. He told me the Harley TC engine is very strong. So that makes me happy.

 

Old Gunny, as you probably know, ported and polished heads can mean a lot of things, especially if done by the wrong person. I've seen guys with performance carsreplace their high dollar ported and polished heads with some rough stock castings to get their power back. I fell victim of this originally with my heads, as stated by the previous owner, "they were ported and polished", but when I took them off and examined, looked like someone did it all with a hammer and chisel with a littlecoarse sandpaper "polishing" at the end. The good thing about a forced induction turbo is that it will override a few errors to some degree. Had GMR do what they could to clean the ports up, recentlygot themback and they really did a good looking job, but made a lot of other changes so really will never know how much, if any, good the cleaning up did. Hopefully I wont have to get my hammer and chisel out and try to restore to the way it was.

Yes, the TC seems to be a strong engine. Long story made short but when I got this turbo bike from Ebay it ran like crap, badly tuned. My professional background was setting up boosted car/truck engines by dyno tuning so went to work on this bike. Got everything straitened out but could tell the rear cyl was using a little oil after all of this but still put 25000 miles on it before I decided to tear it down and take a look at things. Point being is, thisturbo TCenginesure took a badbeating with that mis-tune and reliablystayed together until I made a winter teardown project of it. Have fun with your combo, also sounds like a strong running, reliable combination.