Rebuilding a head for the first time. Looking for some help!

zoolew

zoolew

Member
So I just took my head completely apart for the first time and Im looking for some help as to what I should do next :4: Ive already made some posts about the rust in the intake, which I found out today IS NOT the cause of my seized valve problems. After removing the valve springs and such I realized that the top of the intake's valve guide is where the valve is getting stuck. I tried slipping the intake valve through the exhaust valve guide to see if it was the intake valve, not the guide, but it slipped through as it should. I also tried slipping the exhaust valve through the intake valve guide and the same thing happened, it got stuck while going through the top of the guide.

I took some pictures to you you all to see if theres any evidence of a problem that I cannot see (in order: intake port, intake valve, exhaust valve, exhaust port)
intake valve.jpgvalves.jpgExhaust valve.jpg

Also I have access to a sand blaster for this project. Is it possible/safe to sandblast the head and valves?

Thanks again guys! -Joe
 
ctbale

ctbale

Member
Scotch brite and small wire brushes and time, thats what I use on most of the head. The correct way to fix it is with a reemer, but maybe a 1/8" standard screw driver with a ball of scotch brite might de-burr that guide bore. Or a high quality rat tail file? These bikes get worked on by all kinds in third world countrys so think like them. Remember to lap the valves. I chase all the threads, 6mm and 10mm taps ($10 total) And I know I am going to get grief for this, oven cleaner for 2 to 3 hours after all the manual labor is done. Then hot soap and water in the kitchen sink, then blow dry with a blow gun. From your picture the mating face on the exh valve is beyond lapping?
 
6

69ST

Well-Known Member
I'd replace both valves, along with the springs & seals - also cut the valve seats, just prior to lapping the new valves. Oven cleaner isn't a bad idea, especially for the exhaust port. Look for one containing sodium hydroxide. I'd use a small bottle brush, wear protective gear (long rubber gloves, goggles) and work quickly. Leave the chemical soup in place just long enough to clean the metal, then rinse thoroughly. Otherwise, you may end up with blackened aluminum.

I wouldn't use sand on a head casting. Glass bead, or walnut shells are best; the former works much faster, the latter is safer. Do one port at a time. Insert a valve, from the spring side, to shield the guide from blast media. Make a shallow funnel from scrap sheet metal and use it to shield the valve seat from the blast media, if using glass. No point in exposing the valve seat to any kind of abrasive, expect the cutting stone & lapping compound, even if the surface is pitted. I also wouldn't use glass bead on the head gasket mating surface.

A finish reamer is the right tool to attempt cleaning-up the tight valve guide. If rust is causing the problem, inspect it carefully, post-reaming. Any rust that remains indicates pitting...and time for a new valve guide. Replacement guides are cheap enough that "third world rebuild techniques" aren't worthwhile. Do the job right and recoup the added expense in years of trouble-free running.

I do the seat cutting & lapping next-to last, just before final scrubbing. Scrub every passage, hole & threaded boss, using a small rifle brush & a parts washer, followed by a thorough blowing-out with compressed air. Immersion in mineral spirits, followed by a thorough spray-out with brakleen can be substituted, if you lack either a parts washer and/or compressor.
 
D

dartgt

New Member
I just tore down the motor of a z 50 1974 model. What worked terrific for cleaning all the carbon and crap off the head, ports and valves was one of those gallon cans of carb soak type cleaners. Just put the parts in and let them soak for a day. Remove and rinse in your favorite cleaning solvent and you are good to go ! This stuff took every bit of crud off the head and valves. It wont do anything to corrosion though.

What I used to compress the valve springs was crude but effective. I put one of the valve lash covers under the head and shoved down on the spring with a drum brake nail spring remover, used a magnetic retriever to get the keepers out. It worked and nothing got damaged. I suppose you could use a C clamp and some pieces of oak cut in an open ended semicircle too.
 
6

69ST

Well-Known Member
The carb immersion cleaner is a great idea, although the stuff isn't cheap. Be aware that there are two types. Solder Seal brand is preferred. The other type positively reeks and has real staying power on anything it touches, including hands & clothing:painkiller: You'll smell it in your nightmares(!)

"Back in the day", I made a valve spring compressor tool from a cracked deep-well impact socket, cut large "windows" along two sides, then welded a flat washer to the open end. Even HD valve springs are pretty easily compressed by hand, using an 8" socket extension as a handle. Not as easy a real compressor, but workable on a shoestring budget.
 
ctbale

ctbale

Member
the valve spring compressor i got was $42 delivered to my door (ebay? cant remember) Its pretty nice, clamp it in a vice, then clamp the head with it and can use both hand to insert the valve keys.
 
zoolew

zoolew

Member
Thats why I used a vice grip. All that I had to do was adjust it to the right compression and it will keep itself clamped. I was going to buy a valve spring compressor, but I figured that it would be better to buy more parts to fix the head than a compressor.
 
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