1970 CT70H Manuf. date 6/70 ser# 118130 other shop could not fix

Hi kirbby! thanks! ..yup spun it with drill spark plug OUT just to check spark.....have NOT checked cam timing...you bet i will tommorrow!!! Thanks


the spark plg/coil. points new and super clean and new coil and ngk boot (maybe knockoff ngk) have jumper inplace from bk wire on stator to coil bypassing harness........kinda been over that route about 6 times but have infinite patience......will fatten up the point gap to 16...backatcha in a day or soon...thanks again

One other thing that I don't think has been mentioned. Your flywheel is the Mitsubishi to match your stator, yes. It has the advancing mechanism inside. Maybe post a pic of that mechanism in case we might spot a problem there. Also, if that mechanism was ever removed, it could have been put back 180° off. Might be worth spinning it 180 for a try.

kirrbby said:

Also, if that mechanism was ever removed, it could have been put back 180° off. Might be worth spinning it 180 for a try.

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Thinking about this...if it were 180 out, I think the points cam lobe would be 180 out, and you would have not been able to open and close the points at the flywheel marks.
I think it would be a pretty obvious problem.

good morning Kirrbby...will check cam timing after noon today (T mark on stator with piston at tdc (valves closed, straw in cylinder trick ) and "o" on cam gear at pointer mark on case.)
...if that turns out ok i'll pull the flywheel and post pics..it DOES have the advance mechanism inside the flywheel. the 2 weights move freely, but will post pics..

thanks again

I'm baaaaack all! Cam timing was dead on.....however......at TDC, when i checked the lash on the intake valve there was NONE. Exhaust was fine. I loosened the nut and removed the valve adjusting screw, there was STILL no lash. The valve spring retainer was up against the bottom of the rocker arm..

I pulled the head..and buffed the inside of the combustion chamber for you to take a peek...the intake valve has worn to a very thin rim around the very edge of the face. and was even with the face of the combustion chamber, no discernible margin..
..there is no angle to the valve seat, nice and smooth..

No lash to me equals a loss in compression as the valve doesn't seat..
what puzzles me is why 150psi compression...

A valve can be severely tuliped and still seal well, though probably not for long. You'll have a problem if the seat, valve face, or both need to be resurfaced...or the the amount of valve recession is so extreme that there's no valve lash possible. At that point, no choice but a new valve + three-angle valve job. FYI, it's almost always the intake valve that wears...rarely the exhaust, or either valve seat. With 150psi cranking compression, the motor should run well until the lash goes away...creating an unwanted thermal compression release...if everything else is functioning as it should.

kirrbby said:

Thinking about this...if it were 180 out, I think the points cam lobe would be 180 out, and you would have not been able to open and close the points at the flywheel marks.
I think it would be a pretty obvious problem.

Click to expand...

Great insight! I'm siting here wondering "wtf didn't I think of that, before now?" Not sure if that's true but it sure seems logical and with the beautifully direct simplicity of a correct conclusion. With a removable advance mech. reversed, you should get the occasional light pop and nothing more...once enough fuel has been ingested. The ignition fires every crankshaft rotation...once on the compression stroke and the "waste" spark on the exhaust stroke.

morning gents!
Yup its got me thinking too.. with the obvious valve lash issue, the shop owner decided to go the valve job first,..lets see where that goes....will send pics of inside of flywheel as well. I agree that the engine should have at least started.
Why would some bonehead have reversed the weights...ah ha!
He may have thought that another bonehead reversed them before him...got it!

talk back in a bit..thanks again for your insight...

walt

I think it usually happens when someone removes it to clean and lube etc...trying to do right. Then put it back not knowing that it can be installed the, or A, wrong way.

It's a bit of a longshot...but still, it's a possibility.

Your valve job isn't going to help with the spark, but it's still a good catch.

waltinbatonrouge said:

the light dims only very slightly 100 degrees after the F mark

Click to expand...

Looking back...this might indicate that the timing advance IS 180 out.
...or 100 out. lol

hmmm, i totally agree..the little beast should have started with the tulipped valve..run crummy or at least tried....

so..just thinkin...i should be able to pull the flywheel, look at the relationship between the points cam, points and F mark and see whether its close or not..its only going to be one of two positions, either right on or not even close...I'm going over to the shop to do that today.. will send pics

its like a monkey on my back....i just gotta know.......aaaaaaahhhhhhh
walt

Oftentimes, they won't won't run with a tuliped intake valve...because they leak, badly. The intake port will be blackened from the reversion; it's a slow, gradual, process. That said, if you're getting 150psi cranking compression, the motor should run strong. And a clean intake port means that it has been sealing well. Turning the engine over, by hand, you should feel strong resistance on the compression stroke.

IDK that the advance mechanism has been R&Rd. Not many guys even think to do so, let alone take the time. When I rebuild a 4-speed engine, the entire ignition assembly is just part of the job. I like the removable point cam. When they're rusty, the rust can be removed easily and the cam polished (if one has the wherewithal to polish steel)...good as new. I also add index marks to insure the assembly goes back with the same orientation it had pre-removal. I'd suggest looking closely at the mounting screws. They take a bit of effort to remove and, once R&Rd they'll be easier to remove a second time. If the screw heads look perfect, and the first one fights you when you attempt to break it loose, chances are good that the advance mech. has never left the flywheel since it was assembled at the factory.

We should have the almost new head in later this week...I'll check the flywheel then too

thanks again walt

Hi..sorry its taken so long to get back to you helpful gents...ordered / received new head...vendor sent 50cc head ...managed to send it back after ebay screaming match." we sent 70cc head, no you didn't" , "you ordered 50cc head, no we didn't etc etc" .....70cc head on the way..."I'll be baaaaack"

walt

hmmm.yup me again...shop owner called me again...he finally received correct head...told me that the 70H head has domed piston...thats why he kept receiving wrong head...anyway installed brand new 70H head,

valve's adjusted and checked by shop owner.. timing on, ...150 psi...hot spark, points set again for the umpteenth time...still just a tiny pop, even with starter fluid...

Hes about ready to throw in the towel too ...lots of hours on this one..

I don't quit as easily...i'll check the 180 degree out advance mechanism tomorrow..

since we've met i've finished both a hydrolocked grizzly 700 rebuild and a very low hour beat up grizzly 700 mud bike....without so much of a whimper

but this lil honda is proving to be quite a battler..

thanks again walt

Based on what you just posted in #34, you're pretty well down to the advance mech being 180-degrees out. As best I can determine, everything else has been eliminated and these motors are nowhere near that complicated.

Thinking out loud- Would a fool proof way to install a 4 speed points cam the correct way the first time would be to line the tallest point of the cam the same way the T on the flywheel points?

I just apply paint dots.

Or does the cam lobe point toward the keyway? Seems like there should be a reference point we could figure out now to speed up troubleshooting in the future. If advance cam was 180 out and the points were set when the T was lined up wouldn't they actually be setting the points when the rubbing block was on the lowest point of the cam, start spinning the flywheel by hand and looking through the holes should make the points open up way wider when it finally comes around to the high point on cam. Kirrbby probably has one he could check after his video shoot, but maybe he's out signing autographs from all the fame.

Agreed.
I think it should be pointing toward the T, kinda...upper half of the flywheel. I do have the stator and cases from that motor handy. I'll try to get some pics tomorrow...if I can pull myself away from my fans

I marked the approximate high spot on the points cam with a arrow. I think it's safe to say that this keyways IS the target. It's about 90 degrees from the T...maybe exactly 90 degrees. And you can see that's about where the rubbing block on the points is too.