Top End Noob

[MisterCinders]

Now starts the Winter of my discontent . . .

Well, I need my head examined. This is all new to me, so I am starting a thread for advice and to recount my adventures (those who cannot do, . . . ).

Here are the basics:

1978 GS750 with VH 4-1 and K&N Pods.

Known Issues:

A PO botched a spark-plug expansion on the No. 3 cylinder such that the expander is forever grafted to the plug instead of the cylinder head. Even if the bike were running flawlessly, I need to pull the head to rehab that expansion. I have the Sav-A-Thread kit for this, but cannot do the work with the head in place, or metal bits will fall into the engine.

Of course, the engine does not run flawlessly. The No. 3 plug shows oil-fouling, so something is up in there. It also idles a bit rough, even after much trial-and-error in jetting and carb cleaning, and I think that No. 3 cylinder is a culprit. I could not get a compression test because the tool will not thread into the badly expanded plug hole. It almost fits, but not quite.

The other three cylinders have low compression but not terrible ? showing about 110 psi on a dry test.

Da Plan:

• Pull the head and cylinder block
• Inspect and repair/replace valves
• Inspect and repair/replace piston rings
• Clean everything up
• Replace all gaskets and o-rings
• Win valuable prizes

Shopping List:

To prep for this project, I plan to obtain the following:

• Valve compression tool
• New piston rings
• New valve guides
• Extra shims to readjust the valves when done
• High Temperature RTV Silicon (to lock in the new insert)
• New gasket set to put it all back together
• New exhaust header bolts (the current ones are pretty rusty and may not survive the encounter)
• New exhaust gaskets

Some engine cleaner/polish to pretty her up a bit

Other possible items:

• New chain? The current chain looks OK, but what do I know?
• Cylinder honing tool? Still looking into this, and if it is too expensive, I may opt to have a bike shop do any honing needed. Same goes for valve lapping, and other machine work.
• New valves, if any are damaged, bent, etc. Should I just swap the valves "while I am in there"?

I have the Service Manual and the Clymer's Guide for the bike. Unlike the carb cleaning/rebuild guides, I have not found any "walkthroughs" for this endeavor. If there are any out there (I am looking at you, BassCliff), please advise.

Otherwise, as I begin this adventure, what am I missing?


Pointers, tips, anecdotes, mockery are all welcome.


TIA

 

[hampshirehog]

I'd wait until I'd pulled it apart before buying anything - things might be worse or better than you thought.

Pop photos up on here while you're doing the strip down; we can all argue (sorry, offer advice) about what we would suggest you do.

 

[MisterCinders]

Thanks for the tip.

I will need everything in the first list but the piston rings and maybe the shims for sure. Nevertheless, I will probably pace out the buy orders, as the work progresses.

 

[gearhead13]

Valve guides should be measured for wear, might not need to be replaced, new guides means more expensive machine work (new seats cut). Cam chain should be ok unless there are tons of miles on it, there are measurements for it to check to see if it is stretched too far. Have you had the exhaust off? Do you know if the bolts are frozen or not?

 

[almarconi]

Don't forget valve stem seals and a big bucket o cash. Have you priced oem valves and components yet?

 

[MisterCinders]

Don't forget valve stem seals and a big bucket o cash. Have you priced oem valves and components yet?

Actually, valve stem seals (i.e., the ones that don't survive valve removal) are what I meant for the must-have list.

 

[tkent02]

You might consider getting a used head instead of fixing that one. They are dirt cheap, why take a chance with a bogus repair?

 

[MisterCinders]

You might consider getting a used head instead of fixing that one. They are dirt cheap, why take a chance with a bogus repair?

Thought about it. Might snap one up on eBay to avoid the repair (or if the repair goes pear-shaped).

 

[Graham]

Never had any good luck fixxing sparkplug threads, waist of time. If your going to just replace the rings and not bore it then get one size over bore rings and gap the rings to spec (grind end of the rings to get the right end gap). Always hone cylinders when you rering. Have the valves and seats cut with new guides done by a pro.
If you shortcut on the top end now, you could get a chance to redo it agian soon.

 

[Big T]

Replacing the cam chain guides is a must if you're tearing down the top end. They're old, they're plastic, they keep your valve train intact

Also, service the cam chain tensioner per Brians site

Are we up to $1,000 yet?

As for what needs replacing, follow Nessism's mantra

And yeah, a new head would be cheaper and faster. You can get it blasted, replace the valve stem seals and check the guides and valve sealing. Plus, you won't have any snapped off exhaust bolts to get machined out.

 

[MisterCinders]

You might consider getting a used head instead of fixing that one. They are dirt cheap, why take a chance with a bogus repair?

Define "dirt cheap." eBay shows a bunch of cylinder heads with prices (including the stealth premium for "shipping") from $75-100.

That might be worthwhile, but help me read the tea leaves on condition.

For instance, the photos of the bottoms (top of the chamber) sometimes show rust, others show black carbon. Which is easier to deal with for clean-up?

Compare this:

http://cgi.ebay.com/ebaymotors/ws/e...8320619&viewitem=&sspagename=STRK:MESINDXX:IT

to this:

http://cgi.ebay.com/ebaymotors/HEAD...0296986QQptZMotorcyclesQ5fPartsQ5fAccessories

and this:

http://cgi.ebay.com/ebaymotors/77-S...2185061QQptZMotorcyclesQ5fPartsQ5fAccessories

Any clues to educate this consumer?

 

[Big T]

The dark carbon is normal and will wire brush or blast right off

The rusty stuff is no problem

Where it becomes a problem is at the valve seats - if they're pitted, machining is required. You can't see this in the photos

I would ask the sellers if all the bolt holes are clear, broken fins, plug holes intact and go for it.

You couldn't get your damaged head rewelded and retapped for the $100 cost of the "new" head

 

[MisterCinders]

The dark carbon is normal and will wire brush or blast right off

The rusty stuff is no problem

Where it becomes a problem is at the valve seats - if they're pitted, machining is required. You can't see this in the photos

I would ask the sellers if all the bolt holes are clear, broken fins, plug holes intact and go for it.

You couldn't get your damaged head rewelded and retapped for the $100 cost of the "new" head

Thanks for the info on the rust/carbon.

As to the damage on my head, it does not need rewelding. The retapping would be merely chasing the threads on the insert hole and installing (properly) a new insert. I have the kit for that already. Indeed, the insert that is stuck on the old plug and that threads into the cylinder now matches the insert in the Sav-A-Thread kit. So I think that repair could be pretty straight forward.

I may still spring for a "new" head in case I screw up the plug hole job.

 

[Graham]

Thanks for the info on the rust/carbon.

As to the damage on my head, it does not need rewelding. The retapping would be merely chasing the threads on the insert hole and installing (properly) a new insert. I have the kit for that already. Indeed, the insert that is stuck on the old plug and that threads into the cylinder now matches the insert in the Sav-A-Thread kit. So I think that repair could be pretty straight forward.

I may still spring for a "new" head in case I screw up the plug hole job.

Steel plug inserts and an air cooled head don't work well together. The threads on the plug tend to melt to the insert (plug overheating). Been there and done that. You will need a new insert everytime you change the plug.

 

[gs road racer]

Never had any good luck fixxing sparkplug threads, waist of time. If your going to just replace the rings and not bore it then get one size over bore rings and gap the rings to spec (grind end of the rings to get the right end gap). Always hone cylinders when you rering. Have the valves and seats cut with new guides done by a pro.
If you shortcut on the top end now, you could get a chance to redo it agian soon.

Take it to a professional...this can be done with the engine together. Nothing with repairs is about luck it's good tools and the skills to use them. If you don't have the skills then it's all luck with poor odds.....If you have the skills go for it!

Steel plug inserts and an air cooled head don't work well together. The threads on the plug tend to melt to the insert (plug overheating). Been there and done that. You will need a new insert everytime you change the plug.

Graham not meaning to pick on you but those actually do work well, I prefer helicoil inserts but they are much harder to install (higher level of skills needed). If you had plugs melting onto an insert you've got other problems...more likely corrosion stuck them together use an antiseize compound on plug threads (SPARINGLY)

 

[Nessism]

Thanks for the info on the rust/carbon.

As to the damage on my head, it does not need rewelding. The retapping would be merely chasing the threads on the insert hole and installing (properly) a new insert. I have the kit for that already. Indeed, the insert that is stuck on the old plug and that threads into the cylinder now matches the insert in the Sav-A-Thread kit. So I think that repair could be pretty straight forward.

I may still spring for a "new" head in case I screw up the plug hole job.

Why not just install the new insert now? A few aluminum chips in the cylinder won't hurt anything, plus if you grease up the tap before chasing, there shouldn't be much if any chips at all.

 

[headsbikesmopars]

Mr. Cinders,
I believe that some material from the head has already fallen into the cylinder and scored / taken out the rings in #3. That expains the oil in #3. Yes pull it down but don't buy anything untill you KNOW. Freshen it up with new rings, don't forget to hone first,.. AFTER you check the tapper in the bores. Good idea to pick up another head it will cost as much to have the plug threads repaired by a pro. You will need to freshen the seats and lap the valves anyway even with the 'old' head so no additional real expense there. Have the deck cleaned up with a .005 clean-up mill. Good luck and keep us informed as to your progress..we are all still learning.

Terry

 

[Ranger]

Take it to a professional...this can be done with the engine together. Nothing with repairs is about luck it's good tools and the skills to use them. If you don't have the skills then it's all luck with poor odds.....If you have the skills go for it!



Graham not meaning to pick on you but those actually do work well, I prefer helicoil inserts but they are much harder to install (higher level of skills needed). If you had plugs melting onto an insert you've got other problems...more likely corrosion stuck them together use an antiseize compound on plug threads (SPARINGLY)

I have to agree, I've never had a problem using helicoil even with an LS7 engine. You shouldnt have a problem with metal at all and like was said using grease on the tap will catch most of it and using compressed air helps to blow most of it out.

 

[Graham]

Take it to a professional...this can be done with the engine together. Nothing with repairs is about luck it's good tools and the skills to use them. If you don't have the skills then it's all luck with poor odds.....If you have the skills go for it!



Graham not meaning to pick on you but those actually do work well, I prefer helicoil inserts but they are much harder to install (higher level of skills needed). If you had plugs melting onto an insert you've got other problems...more likely corrosion stuck them together use an antiseize compound on plug threads (SPARINGLY)

Sparkplugs require some cooling; inserts and Helicoils do not transfer heat well to an aluminum air-cooled (high temp) head. They are fine for other bolts and studs but not sparkplugs. Inserts can be used on liquid cooled heads with little trouble. You will never buy a remanufactured head with a insert or Helicoil in any sparkplug hole. The professional way would be to weld the sparkplug hole up and re-drill then tap.

If the head and the repair is short term than do it. But I doubt you will get 50000 miles out of an air-cooled head with a sparkplug insert. If your going to do a top end then why waist money on a good valve job for a jacked-up head that you could get used for the price of the rings and/or gaskets? Why be cheap and do it half a$$. But you get what you pay for.

BTW, I am a professional motorcycle mechanic and shabby work does not leave my shop like using inserts on sparkplugs.

 

[MisterCinders]

I am now looking into obtaining a replacement head.

Will wait to see what's inside before making other purchases. Might also price out what it would cost to have the valves and pistons done if I handed the top end over to a pro.