Planet Minis

badphish · 08-29-2006, 07:01 AM

When turning the motor over by hand it gets tight at TDC. I havn't tried to force it past because of the possibility of a valve hitting. Is there a way to test to see if there is a valve hitting the piston. I was thinking something like plastigauge only thicker. It is one of the 72cc bore kits with a crf head on an 88 or 91 z50 bottom end but this shouldn't cause an issue asn the parts are all interchangeable. The piston is installed with the intake reliefs up

badphish · 08-29-2006, 07:22 AM

Pulled the topend again to double check everything and it is the exhaust valve thats hitting above the relief cut out. It is prolly 3/32 above the top of the relief. What are my options?

arlindsay1992 · 08-29-2006, 07:23 AM

Pull the head off, put a bit of Play Doh on the piston, and then torque everything down and set the timing. Turn it by hand 2 full rotations, and then pull the head off. Check the playdoh. It should not be exessivly thin anywhere. If the piston is hitting the valve, you will have to get a different kit.

arlindsay1992 · 08-29-2006, 07:24 AM

You posted while I was typing so my answer may seem redundant. Now that I've read you most recent post, I think you need a different kit, or maybe just a different head.

thorwarrior915 · 08-29-2006, 08:15 AM

Are you trying to run a domed piston with a stock CRF50 head? If so that isn't gonna work. The piston should be a flat top piston to work with a CRF50 head.

Kurlon · 08-29-2006, 08:20 AM

You may be able to just grind out the exhaust valve relief enough to clear. Be sure to check your work with play-doh once it turns over cleanly.

badphish · 08-29-2006, 08:30 AM

thought about that already it's alot of material to remove i'm wondering if the piston is for a 70 head. I have a chinesse head out of 90 or 100 quad that i will try first

badphish · 08-29-2006, 06:01 PM

it is a domed piston can i just open up the exhaust relief to clear? How much clearance should i have between vavle and piston?

arlindsay1992 · 08-29-2006, 06:09 PM

If you want, I can sell you a used 1984 Z50R head. It has valves, cam, cam sprocket, one cam sprocket bolt, no adjusters, rockers and rocker pivots, and a right side cover(above spark plug). $50 shipped. It will make it so you won't have to grind your piston and if you ever sell it people won't think it's f_ck_d up.Personally I would never grind a piston. It just doesn't seem smart. I'll get pictures of the head in a few minutes.

arlindsay1992 · 08-29-2006, 06:10 PM

Oh, and the stock Z50R head has larger valves than a stock CRF50 head. Just another advantage to a new head.

arlindsay1992 · 08-29-2006, 06:30 PM

So here they are. Also I'll give you the only gaskets I have to fit this head. I won't need them anymore so you can have them.

It came off of a strong running engine and was well maintained for as long as I had it. Oil changed and valves adjusted regularly.

dirtbkr188 · 08-29-2006, 06:35 PM

Make sure the head from the quad will fit properly on all four engine studs all the way down in place, and do not force it, if it is reluctant to slide down. Some of the Chinese-made heads are off by a mm or so, hardly noticable to the eye, but enough to not let it seat properly on top of the cylinder.
Chances are, if the head fits easily, and it is a 28 tooth cam sprocket, you will probably be able to use it. As qwokie and others has stated, make sure you cycle it through a couple rotations by hand, to make sure nothing is hitting or binding.

dirtbkr188 · 08-29-2006, 06:38 PM

...and, if you buy qwokie's old head, make sure you remove the old exhaust gasket, before trying to stuff a new one in there...

arlindsay1992 · 08-29-2006, 06:42 PM

Man, that was a long time ago on another forum! How can you still remember that? Anyway, a new gasket won't fit unless you take out the old one. Take my word for it.

badphish · 08-29-2006, 07:03 PM

i actually have 2 z50 heads i give one of those a try. thanks for the heads up on stud differences will measure it before i try it

badphish · 08-29-2006, 07:37 PM

same issues with the z50 heads since they are a long rod motor would a head from a short rod motor still have good compression? starting to think the die grinder is the solution to this.

arlindsay1992 · 08-29-2006, 09:04 PM

What year Z50 head did you try? In 1982 the heads were changed on Z50Rs. Depending on what you used, there may still be other options besides grinding you piston.

badphish · 08-29-2006, 09:34 PM

tried an 91 and a believe 87 or 88 still have one off an 80 which is the short rod motor which in therory might work but would lower the compression.
the best solution is to try a head of a xr70 or a chinese head with bigger vavles as i believe this might be for the 70 head.

badphish · 08-30-2006, 07:40 PM

I tried the big vavle head. No clearance issues. except I forgot the cam sprocket at the shop and the center hole is larger on the atv head.

arlindsay1992 · 08-30-2006, 09:06 PM

So did the hole size cause any problems? Did you get it running yet?

08-29-2006, 07:01 AM	#1 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	new top end binds at TDC When turning the motor over by hand it gets tight at TDC. I havn't tried to force it past because of the possibility of a valve hitting. Is there a way to test to see if there is a valve hitting the piston. I was thinking something like plastigauge only thicker. It is one of the 72cc bore kits with a crf head on an 88 or 91 z50 bottom end but this shouldn't cause an issue asn the parts are all interchangeable. The piston is installed with the intake reliefs up

08-29-2006, 07:22 AM	#2 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	Pulled the topend again to double check everything and it is the exhaust valve thats hitting above the relief cut out. It is prolly 3/32 above the top of the relief. What are my options?

08-29-2006, 07:23 AM	#3 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	Pull the head off, put a bit of Play Doh on the piston, and then torque everything down and set the timing. Turn it by hand 2 full rotations, and then pull the head off. Check the playdoh. It should not be exessivly thin anywhere. If the piston is hitting the valve, you will have to get a different kit.

08-29-2006, 07:24 AM	#4 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	You posted while I was typing so my answer may seem redundant. Now that I've read you most recent post, I think you need a different kit, or maybe just a different head.

08-29-2006, 08:15 AM	#5 (permalink)
thorwarrior915 3rd Gear Member Join Date: Dec 2003 Location: Malone, NY Posts: 4,549 My Mood:	Are you trying to run a domed piston with a stock CRF50 head? If so that isn't gonna work. The piston should be a flat top piston to work with a CRF50 head.

08-29-2006, 08:20 AM	#6 (permalink)
Kurlon Super Moderator Join Date: Feb 2005 Location: Windham, ME Posts: 8,301	You may be able to just grind out the exhaust valve relief enough to clear. Be sure to check your work with play-doh once it turns over cleanly.

08-29-2006, 08:30 AM	#7 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	thought about that already it's alot of material to remove i'm wondering if the piston is for a 70 head. I have a chinesse head out of 90 or 100 quad that i will try first

08-29-2006, 06:01 PM	#8 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	it is a domed piston can i just open up the exhaust relief to clear? How much clearance should i have between vavle and piston?

08-29-2006, 06:09 PM	#9 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	If you want, I can sell you a used 1984 Z50R head. It has valves, cam, cam sprocket, one cam sprocket bolt, no adjusters, rockers and rocker pivots, and a right side cover(above spark plug). $50 shipped. It will make it so you won't have to grind your piston and if you ever sell it people won't think it's f_ck_d up.Personally I would never grind a piston. It just doesn't seem smart. I'll get pictures of the head in a few minutes.

08-29-2006, 06:10 PM	#10 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	Oh, and the stock Z50R head has larger valves than a stock CRF50 head. Just another advantage to a new head.

08-29-2006, 06:30 PM	#11 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	So here they are. Also I'll give you the only gaskets I have to fit this head. I won't need them anymore so you can have them. It came off of a strong running engine and was well maintained for as long as I had it. Oil changed and valves adjusted regularly.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

08-29-2006, 06:35 PM	#12 (permalink)
dirtbkr188 3rd Gear Member Join Date: May 2004 Location: New Jersey Posts: 2,972	Make sure the head from the quad will fit properly on all four engine studs all the way down in place, and do not force it, if it is reluctant to slide down. Some of the Chinese-made heads are off by a mm or so, hardly noticable to the eye, but enough to not let it seat properly on top of the cylinder. Chances are, if the head fits easily, and it is a 28 tooth cam sprocket, you will probably be able to use it. As qwokie and others has stated, make sure you cycle it through a couple rotations by hand, to make sure nothing is hitting or binding.

08-29-2006, 06:38 PM	#13 (permalink)
dirtbkr188 3rd Gear Member Join Date: May 2004 Location: New Jersey Posts: 2,972	...and, if you buy qwokie's old head, make sure you remove the old exhaust gasket, before trying to stuff a new one in there...

08-29-2006, 06:42 PM	#14 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	Man, that was a long time ago on another forum! How can you still remember that? Anyway, a new gasket won't fit unless you take out the old one. Take my word for it.

08-29-2006, 07:03 PM	#15 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	i actually have 2 z50 heads i give one of those a try. thanks for the heads up on stud differences will measure it before i try it

08-29-2006, 07:37 PM	#16 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	same issues with the z50 heads since they are a long rod motor would a head from a short rod motor still have good compression? starting to think the die grinder is the solution to this.

08-29-2006, 09:04 PM	#17 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	What year Z50 head did you try? In 1982 the heads were changed on Z50Rs. Depending on what you used, there may still be other options besides grinding you piston.

08-29-2006, 09:34 PM	#18 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	tried an 91 and a believe 87 or 88 still have one off an 80 which is the short rod motor which in therory might work but would lower the compression. the best solution is to try a head of a xr70 or a chinese head with bigger vavles as i believe this might be for the 70 head.

08-30-2006, 07:40 PM	#19 (permalink)
badphish 1st Gear Member Join Date: Feb 2006 Posts: 146	I tried the big vavle head. No clearance issues. except I forgot the cam sprocket at the shop and the center hole is larger on the atv head.

08-30-2006, 09:06 PM	#20 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	So did the hole size cause any problems? Did you get it running yet?