Doctor, I've got no pulse!

I like your sense of humor..... When I was a kid one of my good friends had a H. Can't remember what happened but he had to buy a replacement frame. Later on we both bought the first CR 250's and managed to break those frames as well- happens

Here’s the slight bend on the left shock mount. As it stands I don’t intend to do anything to correct it as I believe any effort on my part would make things worse. I didn’t notice it until I had disassembled the bike down to this point. The original shocks appear to be bowed/bent, and the cans/covers near the top are dented, rusty and have wear holes from the rubbing on the springs. I’ll be sourcing a new set rather than waste time with junk parts.

Those engine mount area stress cracks are semi-common with K0 frames. Why some frames develop these, while others <ostensibly> never do, is a question I don't expect to be answered, definitively. I suspect it's a result of structural improvements (Honda implemented running changes with the frames) and loose engine mounts. The engine is a critical part of the structure...similar to the axle assemblies and swingarm pivot assembly. Loose axles, swingarm pivot bolts and engine mounts are disasters waiting to happen (and thus preventable). I usually add metal when doing this repair...it's probably overkill. One thing I would strongly suggest is carefully inspecting the rest of the triangle area... they usually form cracks on both sides...after the bead blasting. 90% of the time, there will be tiny breaks on the opposite side that only become visible once the surface is clean & uniformly colored. FYI, you caught this at an early stage. Left alone, the cracks not only spread but they first "V", then develop a dendrite (think tree roots) pattern, just like seat pan breakage.

The seat latch mount area, well, we know the cause...using the seat as a lift handle. That's an easy repair. Knock down the metal, just enough to give you a slight (few thousandths of an inch) extra depth for welding, from the top. Once the welds have been dressed, the seat latch hides the surgical scars. And, this also minimizes the amount of finishing work needed on the visible side, in the wheel arch.

It doesn't look like much deflection, in this pic. As long as you can apply the force, needed to straighten the mount, to the short section inboard of shoulder, I think you'll be okay. The shoulder, being a sharp 90-degree transition, is a stress riser. That's where my shock mount snapped-off.

The most common issue I've encountered with bent shock mounts is that the bend extends to the central portion...inside the frame. That alters frame geometry in ways that cause a number of concerns. Chief among them are the pinched-in frame walls and angled seat supports/shock mounts themselves.

"The engine is a critical part of the structure...similar to the axle assemblies and swingarm pivot assembly." Not to mention the foot peg assembly being bolted to the bottom of the engine. That kid in the picture is not sitting on that seat - he is standing on the pegs and that force of him landing is going to go somewhere. Early CR's had the right side peg bolted to the frame so that it could be removed to get the engine out. That peg breaking off on jumps was just one of the frame problems those early bikes had

racerx said:

One thing I would strongly suggest is carefully inspecting the rest of the triangle area...
As long as you can apply the force, needed to straighten the mount, to the short section inboard of shoulder, I think you'll be okay.

Click to expand...

I am expecting to find more cracks once I get it blasted down to bare metal. I had my neighbor do the seat latch area repair from the top because I knew it wouldn’t be visible, I just don’t have a pic of the finished job. With regard to the shock mount, it’s a solid bar inserted through the frame and welded/reinforced with those 90 degree plates that the seat rests on, correct? I don’t know how I’d get enough leverage to pull/push down on the mount bar without threatening the threads, especially without a frame stand.

Speaking of stands, has anyone here made their own engine stand? If anyone has a template, dimensions or measurements they used to create the mounting plate & holes that would be much appreciated. My neighbor is interested in helping more with this project and making a stand would put his welding skills to good use.

airblazer said:

With regard to the shock mount, it’s a solid bar inserted through the frame and welded/reinforced with those 90 degree plates that the seat rests on, correct? I don’t know how I’d get enough leverage to pull/push down on the mount bar without threatening the threads, especially without a frame stand.

Click to expand...

Yep, it's a Mofo of a repair...or, it can be. There's not much working room for chiropractic adjustment to straighten the original. And there's absolutely no way to remove the original without destroying it. That's the main reason I thought about using a "blue wrench assist". Here come the "ifs"...if the bend is localized to the outside of the seat support and if one is skillful with the torch, it may be possible to heat the shock mount just to the plastic stage where it can be muscled back into shape. OTOH, if the deformation extends inside the frame, it's a whole other situation. Getting the center portion of the mount bright, cherry, red without injuring sheetmetal is about as risky as free-climbing a sheer cliff. The "canary-in-the-coal-mine" is frame alignment. If the seat supports are not exactly parallel (outward facing sections) to each other...top-to-bottom & front-to-back, the extreme structural strength of that part of the frame cannot be overcome, with any practical method. Consider some basic geometry & physics...once the mount is bent, the distance between its ends is shortened, that pulls the frame rails inward. Beyond mentioning the extreme vectors involved, I'll spare you a physics lecture; suffice it to say that shock mount does one incredible job of keeping the rear section of the frame stable. Once the tweakage we've been discussing has occurred, that structural rigidity becomes one tough adversary. I'm not holding out on you, there's not much I can really share. As a welder, I'm mediocre at best...except when it comes to sheetmetal. As for metalworking I learned old-school techniques. Hell, at this late date I am old-school. Unfortunately, this means knowing how to improvise, as the situation dictates...real seat-of-the-pants flying. I can replace a shot mount and straighten a bent CT70 frame in a few hours, plus or minus depending on the extent and location of the damage. That said, collision damage is not one thing and thus, neither are the repairs. Bottom line is that every frame has to be considered its own, unique, project...and...a truly irreparable CT70 is a rarity. IMHO, time, persistence and patience should carry you successfully through the process.

Thanks for the info Bob. I’ve looked at my other frame pics I took of the mount and I’m not even completely convinced it’s bent. I’ll take a much closer look the next time I’ve got the frame in front of me.
I just finished watching Kirrbby’s 3 part YouTube video of splitting the cases on the H engine. Thanks Kirrbby, the videos were great and I appreciated that things didn’t go as smoothly as you hoped, it makes you more human . Seems an engine stand isn’t necessary at all with the number of times you need to rotate or flip it, just a 2x6 version of the wood box engine holder seems to be what I need. How do the long rods that go from the case to the top of the head come out? I assume they’re threaded on both ends.

The long studs ARE threaded on both ends. I usually snap a set of vice grips on really tight, down near the engine case to break them loose. Then I tape the threads out on the ends and chuck up a cordless drill to back them out...masking tape works well enough to protect the threads.

I agree about the engine stand. I think they are a cool thing...but I just can't justify the need for one.

I need to purchase a valve spring compressor to continue working on my bike. Is the tool on Amazon sufficient? I’m all about supporting the little guys. But I can’t see a good reason to pay the price that CHP wants for this item. DrATV’s version better be made out of platinum or gold to get someone to spend that much on a single purpose tool

How's 21 bucks? Made in the U.S.A. Wilde tools. ebay item# 131426682516 This is the one I use, very rarely.

X2
I use that same one/type. They sell them for Briggs and Stratton lawnmower/small engine repairs.

https://www.ebay.com/sch/i.html?_fr...leDesc=0&_sop=10&_osacat=6000&_odkw=honda+z50

Why do you guys bother to remove the cylinder head studs?

The only time to remove them is when you are building a 54mm build. They use longer studs.
Otherwise, leave them alone... They are not very hard to clean.

Once you DO take them out, it's a lot easier to do all of your handling and clean up and such. You don't need to put them back in until you have the bottom end all put together and ready for a top end. They're kind of a neusance until then.

Ok gotcha thanks. I have only built one stroker engine and that was an air cooled VW. That must be a different concept because the width didnt change. I never removed Honda studs because I didn't want to chance damaging the threads in the case halfs

I always pull the cylinder studs. It facilitates cleaning, as suggested. But, the not-so-obvious benefit is realized when it comes time to remove the remains of the cylinder base gasket; that's the most stubborn gasket with these engines and you really do want those surfaces clean.

Do keep in mind the clutch, or at least the clutch pack. Any stroker engine is going to make the clutch work harder. At a minimum, go for new plates, discs & HD springs. The TB clutch is also a good good choice...and all-new parts.

If you've made up your mind about the configuration of this engine build, either stop reading here or, be prepared to dismiss what follows. I'm of the "measure twice" camp, i.e. consider all the possibilities at the outset, to limit, or prevent, buyers remorse later. My ramblings can open many cans of worms...and cause migraines.

Since you're going with a new crank, two other things you might want to consider...upgrading the 12v/CDI electrics and 51vs 54mm stroke. Going with a straight 6v-style 51mm crank (TB is the only game, period) is the simplest and least bucks. 54mm will make the most torque, by far, but...you'll need longer cylinder studs, a 69mm tall cylinder and a longer timing chain. As long as you limit bore diameter to 52mm, no case mods are needed. This is probably another couple of C-notes. 12v/CDI offers some nice improvements over 6v breaker point electrics and going with a 12v style crank opens up all kinds of possibilities (beyond what is practical/possible in 6v flavor) but, again, it's additional bucks.

Received my flywheel puller in the mail today. Later this week my valve compressor and several parts from CHP should arrive, which will assist me in disassembly and overhaul of the engine. It’s probably hovering around freezing in the garage, but no need to fire up any heaters or hide parts in the house yet. It dumped nearly 2 feet of snow in about 18 hours at my house over Thanksgiving. Even though I’m only a mile from the Great Salt Lake, its shallow depth and saltiness don’t cause lake effect snow like some of you see in the upper Midwest. The ski resort 40 minutes from my house got over 6 feet so it seems it will be a good ski season this winter.
Has anyone ever had extreme amounts of trouble pulling a flywheel? Just some PTSD about reefing on something too hard kicking in right now. I’m guessing the difficulty on my crusty bike will be more than less, kinda like the difference between these two photos:


Kudos to whichever LilHonda member is responsible for the tearitupfixitrepeat blog. The other manuals sometimes are a bit vague...

This would be the member...and the thread.
https://lilhonda.com/index.php?threads/big-boys-bike.11526/#post-75863

Thanks for the tip. Looks like he went into more detail here than he did on his blog. Either way very useful stuff for a noob like me.