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

maurtis · May 17, 2012

Hi all,

Looking to go with a Puch head soon, mainly for the extra cooling but some more power would be lovely. I have a BGF RB80 engine, which I *think* is the same as the Grubee GT5A SuperHawk. The reason I think they are the same is because both the RB80 and GT5A have the same wider intake port stud spacing, port matched aluminum intake, and 6mm head studs. From all of the descriptions I have read of the GT5A, it seems to match exactly the BGF RB80, except the RB80 comes with an NT carb and 415 chain.

Anyways, the MM head states that it does not work with the GT5A and I think the Pirate head does not either. Bairdco said his friend with a GT5A keeps blowing head gaskets from the heat. I do not have many miles on mine yet, but notice the plug is starting to blue on the outside...

So on to the actual question...

I have searched for posts on using the Puch 70cc head on a 66cc HT motor, and I see that people have done it. With the 6mm studs, it seems that I should be able to bolt it right on.

But I see mixed reports of people saying the compression will go down, and others saying it will go up to like 11.5:1! Since the tools in my garage are a Dremel, hammer, and duct tape, I do not have a compression gauge.

Any WAGs on what the compression might be with running just one head gasket? Or is it a matter of slapping one on, and if the plug and piston do not meet, go for a ride and see if it works?

Mobbin'Deep · May 17, 2012

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

Stock puch head will decrease compression if im not mistake because you have to run double headgasket.

I was running a Puch hi-hi compression head from treatland. Had to double gasket, but it did increase compression significantly. I couldnt pedal start the bike anymore. Had to loosen the spark plug to bleed compression to get it warmed up haha.

You have to drill out the holes on the head, they wont fit stock studs. No big deal with drill press

maurtis · May 17, 2012

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

Sorry, I should have been more specific, I was referring to the 70cc hi hi head from Treatland puch moped 70cc hi hi compression head

Someone mentioned that they did not have to drill their holes out since they had the 6mm studs, as do I. No big deal since my neighbor has a drill press that I can borrow.

So with double head gaskets you still had trouble pedal starting it?

If the stock Puch head lowers the compression, and the "hi hi" head raises it too much, is there just a "hi" head? Maybe this guy: puch moped 70cc hi compression head - old style fins

rustycase · May 17, 2012

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

M, I'd like to ask what plug you are running that it turning blue?
Do you really think the cylinder head does a poor job cooling?

I've seen a few comments by some of the engine builders claiming somewhat more problems with the slantplug head motors.

Perhaps it is related to cooling?

I'll keep an eye on your results here, and if you do get an improvement, I might give a try welding some extra fins on a slant head to see how that works out...

Best
rc

maurtis · May 17, 2012

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

I am running an NGK B6HS. If I can remember to borrow the laser thermometer from the office next week, I can try and get some numbers on operating temp. That should be insightful!

As far as how this head cools, coming from the world of small water cooled 4 strokes and 1600cc air cooled 4 strokes, I have never seen a plug oxidize on the outside and start turning colors, especially this quickly. I have maybe 50 miles on this plug, so it is not like it has been run hard for a long time... It is only bluing near the head so far, which makes sense. I would have just chalked it up to being how these little China Girls run if others had not expressed concern that such a condition was not normal.

DaveC · May 22, 2012

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

The bolts on the China motor and the Puch head have different spacing with the Puch being slightly narrower. Find someone with a drill press or maybe you can use the Dremel to enlongate the holes outboard a bit until it fits.

Kinskeys · May 23, 2012

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

I have a GT5A and have blown 2 head gaskets within a month & it's not even summer yet, please let me know if the Puch head works for you.

haddenboy · May 23, 2012

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

I ran this exact setup on my last bike. They head will absolutly fit with no modifications just like you thought, however whether or not you can fit a socket in between the fins to tighten it all down is another story. My sockets were too big, but my neighbor had a thinner set that just barely fit so I could tighten them down. It will become very difficult to pedal start. I typically had to have my roommate do it for me because with my weight (140) the bask tire would just slide on the asphalt when I release my clutch. My room mate weighs about 200 and he could typically get it started after a few tries. Definetly noticeable gains in the low end. I personally really enjoyed this mod.

maurtis · May 23, 2012

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

Good to know, were you running one head gasket or two? I am 195lbs right now, and while I would love to get that down closer to 180, my love of beer and McGangBangs means that will likely not happen any time soon...

haddenboy · May 23, 2012

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

I had to run 2. Started with one but there was a very noticeable compression leak so I ran two and problem went right away. Only downside to this set up is you will burn your leg a few times. The puch head is wider with the large fins, and on more than one occasion I touched my legs to the sides of it and burnt my leg something fierce.

maurtis · May 23, 2012

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

I look forward to easing the emotional pain, lol. I already burned my left knee once, wearing jeans that had a hole in the knee from wrecking my son's electric motorcycle... .wee.

culvercityclassic · May 23, 2012

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

Maurtis...pull the trigger and purchase the 50cc puch head. Yes I said 50cc. It helps with performance, it's inexpensive and it looks good.

On my two applications I just enlarged the stud holes which I don't think you will need to do since you have the smaller studs. I run one head gasket and 100 octane gas, if you can't find the gas purchase some octane booster and add to your mixture.

Never had issue with the head in my way... laff

http://www.motorcycle-superstore.co...-Gold-Label-Racing-Castor-Octane-Booster.aspx

maurtis · May 23, 2012

culvercityclassic said:
Maurtis...pull the trigger and purchase the 50cc puch head. Yes I said 50cc. It helps with performance, it's inexpensive and it looks good.

On my two applications I just enlarged the stud holes which I don't think you will need to do since you have the smaller studs. I run one head gasket and 100 octane gas, if you can't find the gas purchase some octane booster and add to your mixture.

Never had issue with the head in my way...

http://www.motorcycle-superstore.co...-Gold-Label-Racing-Castor-Octane-Booster.aspx

Wow, the 50cc hi hi head? I want to be able to actually start the bike! Seriously though, the 50cc head and 1 gasket and the compression is not too high? Ah, I see, the compression is low enough with the spark plug shaped hole in the piston laff

I go through so little gas that I would not mind heading in to Austin to get some VP high octane stuff every now and then.

maurtis · May 24, 2012

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

Saw this posted over on MopedArmy and thought it was an interesting side-by-side of the Puch high compression heads:

Kinskeys · May 24, 2012

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

I'd talked to the guys @ Pirate Cycles & they told me that the Pirate Cycles High Compression Head should work on the GT5A so I went ahead & order one, that's the fun part of motorbiking working & tweaking your bike, to make it run better, if it don't work, I'll just order a 70cc Puch head and try that .wee.

maurtis · May 24, 2012

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

Kinskeys said:
I'd talked to the guys @ Pirate Cycles & they told me that the Pirate Cycles High Compression Head should work on the GT5A so I went ahead & order one, that's the fun part of motorbiking working & tweaking your bike, to make it run better, if it don't work, I'll just order a 70cc Puch head and try that

That is stellar news! In about a week I am going to order a new head, probably still one of the Puch heads for grins, but good to know the Pirate Cycles head will fit if things do not go well. I cannot wait to see your update

max350 · May 28, 2012

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

Here is my 66cc engine with a 70cc Puch cylinder head and it works great white a Squish of 1.8 mm! Becomes just right compression for the engine

It is a beast! 15hp 20000rpm! I am just kidding

rustycase · May 28, 2012

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

Wow!
HUGE pipe on that engine, Max!

I hope you post a vid of that motor running a motorized bicycle down the road!

Best
rc

max350 · May 29, 2012

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

rustycase said:
Wow!
HUGE pipe on that engine, Max!

I hope you post a vid of that motor running a motorized bicycle down the road!

Best
rc

You can look at my you tube links xct2

maurtis · May 31, 2012

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

Treatland shipped my Puch 70cc hi hi head yesterday, and SBD shipped two new gaskets. Now time to see if I can get an NGK BR9HIX locally...

So when running two head gaskets, anything in particular that I need to do? I planned on spraying them individually with copper gasket paint and using 60 inch pounds of torque on the head nuts, as I did with the stock head.

My Jaguar CDI should be arriving about the same time, woohoo! I should probably tighten my internal clutch spring before putting the head on. It likes to slip on occasion while starting the bike now, so I figure with a higher compression head it will only get worse...

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

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