Puch head on a 66cc HT bicycle engine with 6mm studs

Re: Puch head on a 66cc HT with 6mm studs

8mm studs require 120 inch pounds and if you don't have the SBP headstud kit you should. A 14mm socket will not fit down in the fins. I think there is a thin wall socket that does but it's like a Snap On socket and they cost, if you can find one, almost as much as the stud kit. The SBP kit has 13mm nuts.
 
Re: Puch head on a 66cc HT with 6mm studs

DaveC said:
8mm studs require 120 inch pounds and if you don't have the SBP headstud kit you should. A 14mm socket will not fit down in the fins. I think there is a thin wall socket that does but it's like a Snap On socket and they cost, if you can find one, almost as much as the stud kit. The SBP kit has 13mm nuts.
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Right, unfortunately I have the 6mm studs on mine. It was said on here that the 6mm studs should be torqued to 60-72 inch lbs. With the regular head, 60 inch lbs has been fine and has not leaked at all, hopefully it is enough for the higher compression head.

The SBP stud kit was the very first upgrade, woohoo!
 
Re: Puch head on a 66cc HT with 6mm studs

Ah, cool. Like I said earlier though, the holes don't exactaly line up. I drilled mine out to a larger size so the Puch head would fit. Not a big deal, though.
 
Re: Puch head on a 66cc HT with 6mm studs

I finally got my NGK BR9HIX spark plug in, which was the last piece I was waiting for to install the new head. I was shocked that I could not find one locally, so I ordered 2.

With the BGF RB80 motor, which I am pretty sure is the same as the Grubee GT5a with 6mm studs, the Puch 70cc hi hi head fits perfectly, I did not need to modify it at all.

I test fit the head without any head gaskets, just to make sure that it would go on, and I verified that the piston will hit the head without the gaskets. I had ordered two new head gaskets for the 6mm 66cc motor from SBP and already coated them in spray copper gasket maker, so I slipped on the gaskets, put on the head, then tightened up the head nuts in a Z pattern.

Unfortunately the only torque wrench I could find that goes down to inch pounds uses the smaller drive, what is it, 1/4"? And my 10mm socket that fits is was too short, so I had to tighten them by feel using my longer 10mm socket on my "regular" socket wrench. So this evening I need to go out and see if I can either find an extension to fit the socket, or preferably a deep socket.

Oh yeah, and I switched to 93 octane a few days ago in preparation for the new head.

Riding impressions: love it! I was afraid my clutch was going to slip, but she fired right up. Noticeably more torque down low and mid range and the engine noise seems a tad less raspy. Usually if I let the clutch out around 10 MPH (this is with a 36 tooth sprocket), I still have to pedal quite a bit to get my 195 lb self going. With the new head, from 10+ she pulls on her own .wee.

I really am not sure about the high end since I think my CDI is unhappy. With the stock head I would start getting what sounds like pinging in a series of machine-gun style spurts starting around 33 MPH, which would kill the power. I could get her up to 37 MPH, but she tops out around there, which feels limited by the pinging. I was hoping going to 93 octane would help, but nope. I get the same behavior with the Puch head, except I get there faster ;)

My Jaguar CDI should be here next week, so we will see if the CDI really was the culprit...
 
Re: Puch head on a 66cc HT with 6mm studs

Thanks for the update! Glad that the Puch head fits and works well, sorry to here about that troublesome pinging is still there. I almost wonder if it is not detonation, but could be the known sloppy piston/wrist pin and bearing that is making the noise?
 
Re: Puch head on a 66cc HT with 6mm studs

maintenancenazi said:
Thanks for the update! Glad that the Puch head fits and works well, sorry to here about that troublesome pinging is still there. I almost wonder if it is not detonation, but could be the known sloppy piston/wrist pin and bearing that is making the noise?
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Thanks for the tip! Searching for "wrist pin noise" turned up this thread, and the sound in the audio clip in the first post is exactly what I am hearing: Weird clanking noise during rides

I do not get as much as he does in the clip, but definitely the same sound.
 
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Re: Puch head on a 66cc HT with 6mm studs

I have a PK68.5/80cc with .060 piston what size Puch head did you use and is it a high comp head??
 
Re: Puch head on a 66cc HT with 6mm studs

truckd said:
I have a PK68.5/80cc with .060 piston what size Puch head did you use and is it a high comp head??
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I went with the Puch 70cc hi hi from treatland: puch moped 70cc hi hi compression head

It seems to increase the compression some but not as much as I expected, which is a good thing. I was afraid that it was going to make the bike very hard to start, clutch slip, etc, but so far no problems. It would have been nice to get a compression reading before and after the swap, but since I do not know anyone who has one and did not want to spend the $ on a cheap one, I just have to wonder. Trying to kick the motor over using the pedals on the center stand seems to take more effort...

Culver mentioned that he used the 50cc head for more compression, but that was a little too bold for me... for now ;)

And I picked up a 1/4" drive 10mm deep socket last night and torqued my head nuts to 72 inch lbs (I used 60 inch lbs on my stock head), and my original torquing by feel was way off, lol. I am shocked that I did not get leaking through the gaskets, but I guess that copper spray-a-gasket really does help!
 
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Re: Puch head on a 66cc HT with 6mm studs

This is what I'm working on and I've got to get it right, as I've mentioned PK68.5/80cc, #5 .060 domed piston, just ported and polished cylinder, getting the chains right so I mounted the engine for pre-stall
 

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Re: Puch head on a 66cc HT with 6mm studs

truckd said:
This is what I'm working on and I've got to get it right, as I've mentioned PK68.5/80cc, #5 .060 domed piston, just ported and polished cylinder, getting the chains right so I mounted the engine for pre-stall
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Gorgeous! Almost sad to see a China Girl in there instead of an old 4 stroke, that is a fantastic looking build!
 
Re: Puch head on a 66cc HT with 6mm studs

Thanks!! I will get a 4-stroker soon but for right now the 68.5/80cc keeps me street legal and for this bike it has the best of the china girls, found out that you can't get the m/m gen ll high comp head anymore and everyone tells me to try the puch high comp head, so I'm try'n to get as much info on this head as possible to get the best for this bike
 
Re: Puch head on a 66cc HT with 6mm studs

Some pics of the Puch head installed. I got the Jaguar CDI installed too, that and the coil are hidden under the red cover. The CDI did NOT cure the pinging noise, seemed to make it worse actually. So thinking a new wrist pin needle bearing is in my near future :-||

Puch_head_installed.jpg


Puch_full_right.jpg


I plan on shortening that throttle cable soon, ugh. And I should have a front drum brake next week, woohoo!
 
Re: Puch head on a 66cc HT with 6mm studs

^ Wow, very nice looking ride Mr Maurtis! That i'm sure will turn some heads. Hmmm, that head also looks real good on there. May have to look into one of those, of course i'll have to break out my drill press. Because my motor has the 8mm studs. Again nice work!

Peace, James
 
Re: Puch head on a 66cc HT with 6mm studs

That is a really nice bike!! What do suspect is causing the wrist pin needle bearing to mess up and what would be a permanent fix, I've never started my engine and am doing all the mods up front so I will not know what was but only what is,what kind of gaskets did you use the stock chinee gal ?
my plan is
Puch head
Dellorto carb
ported and polished cylinder
JNM header exuast port
Jaguar cdi & coil
ngk bh9s spark plug
Pat Dolans intake manifold tube
and if ? I can find some opti2 I'll start the engine off with that insted of something else for the break in and continue through-out use.
 
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Re: Puch head on a 66cc HT with 6mm studs

Oh by the way I make my own cables and if you shorten the cable do it from the larger throttle stop NOT! the one that incerts into the carb, reason being is that you wont't have to either re-place the carb or re-build it because the stop( for any reason? broke) f'd something up inside the carb
making cable stop and shortening a cable isn't as hard as you'd think and there is a thread on this forum that goe's through it step by step, I'll post a pic of my cruiser that I made all cables for, not to blow my own horn but it too is a beautiful bike and has a thirties theme going on. someone on this forum once said " A Cheap bike is Not good! and a Good bike is not cheap!
I'll get a looky loo of Ol' Blue right away
 
Re: Puch head on a 66cc HT with 6mm studs

Here 's Ol Blue hope you like him
 

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Re: Puch head on a 66cc HT with 6mm studs

Truckd, Ol' Blue is nice and clean, awesome build!

I was thinking my issue was the wrist pin bearing since they tend to go bad often on HTs, but it looks like my issue was actually four stroking at high RPM. I leaned up my jet and changed the settings on my CDI, and it seemed to go away, so we will see if it stays that way.

But if you do end up with a wrist pin bearing going bad, apparently they are very easy to replace by just taking off the cylinder and piston, and quality replacement bearings are around $10.

On my last tuning run last night after getting the pinging to go away my clutch took a dive, so working on that today, lol. Good thing I like tinkering as much as riding! My next build will be a 4 stroke, though, it will be nice to have a solid build that does not need quite so much attention laff

*** Update: My clutch issues were caused by the nut holding the bucking bar/sprocket had backed off a few turns. Tightening that up fixed my clutch issues. Went on a nice ride and everything ran great!!!
 
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Re: Puch head on a 66cc HT with 6mm studs

Hey Max what kind of carb are you running and did you do any clutch cable mods to it and wich high comp head are using 70cc Hi Hi comp or 70cc high comp old style finned???
 
Re: Puch head on a 66cc HT with 6mm studs

Maurtis where do you get the wrist pin bearing ? as I don't want to order another crappy one from a Co. that sells the same engine kit and since I already have mine apart why not? just go ahead and do it, what is it exactly called as far as size and or part number bearing, sorry for the questions but I do believe it's refrred to as R&D (LOL) Thanks! for the help.
 
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