Top End rebuild advice needed...

[froldt]

I just got the top end back from the machine shop, valve job is complete! While I should have already been working on this, I now need to decide what to do with the pistons.

If I replace the pistons with the next size up, it will cost me about $450. (Pistons, rings, clips, piston pins - boring and honing)

If I just get new o-rings and get it honed, it will cost me about $130.
If I hone it myself, I will pay nearly the same since I will have to buy the blades.


What are the advantages to getting new pistons? What, then, are the problems that I would face (won't it increase the compression, and then I'd have to mess with the carbs and air-intake and stuff)?
If I just put new rings on, what all is involved in that? Do I need any other parts?

Also, what kind of gaskets do I need? Should I pay the $100ish for a complete top end gasket set, or can I use the silicon gasket material in a tube?

Thanks in advance!

[Guest]

Need more info. What year/model? Why do you need to do anything with the pistons? Did it smoke? Bad compression? Oil consumption? Did it run good before (except for needing the valve job)?

[paintmann111]

Honing might be the best bet. It really cleans up the walls and makes the rings fit a lot better. Depending on the condition of the piston walls, you may be able to hone them and be all set. However, if you can feel a ridge near the top of the wall you may need to bore it out to the next size.

[koolaid_kid]

You will need a gasket set. You can get a complete engine gasket set from Z1Enterprises.com for around $80. It will be Vesrah, which is a good brand.
If you hone it, I recommend the kind with the stones, not the blades (there is a brand name for it, but I forget what it is called).

[Big T]

Never use the silicone. Anywhere. On the engine internals.

And make sure all the grit is cleaned off anything you send out to be worked on. Wipe the important surfaces with a paper towel. Black grit? Get cleaning with a solvent. Especially true after the cylinders are honed.

[froldt]

Need more info. What year/model? Why do you need to do anything with the pistons? Did it smoke? Bad compression? Oil consumption? Did it run good before (except for needing the valve job)?

Sorry about that. It's an 82 GS750T. I purchased this bike, rode it for maybe two weeks, and it refused to start. It has about 42k miles on it. After rebuilding the carbs and some other work, a mechanic looked at it and told me I needed a valve job.
My goal with this bike is to use it for a daily rider, and get rid of my car. The mechanic told me that since I had it apart, I might as well redo the pistons, and new ones would be better (long run) than just new rings.
The compression was horrible (didn't even register on one of the cyls). It didn't smoke any, and I didn't get to ride it enough to know about oil consumption.

Honing might be the best bet. It really cleans up the walls and makes the rings fit a lot better. Depending on the condition of the piston walls, you may be able to hone them and be all set. However, if you can feel a ridge near the top of the wall you may need to bore it out to the next size.

The walls are in good shape. They're in excellent shape considering the mileage on the engine. The pistons themselves have only light evidence of rubbing, not enough to cause any worry. With 4-6 years of riding ahead of me (last through college, I hope), though, I was told the best option is to just bore it and put a whole new set of pistons in there.

You will need a gasket set. You can get a complete engine gasket set from Z1Enterprises.com for around $80. It will be Vesrah, which is a good brand.
If you hone it, I recommend the kind with the stones, not the blades (there is a brand name for it, but I forget what it is called).

I looked up the specific gasket set for my bike, and for some reason the $100 range stuck in mind. I can't check it on this computer (something about the javascript), but I'll double check the prices tomorrow at work. Gaskets it is, then...

I didn't realize there was anything but the stones. I figured that "blades" just meant the stones.

[mark]

No need to get oversized pistons just because your pulling the block. When you pull the block, take it to a machine shop and they can measure it to see if its within spec. It may be fine. Put in new rings (with proper gap of course), hone it, and you're good to go.

My cylinders were in great shape when I pulled my block off. Except for a huge scratch in one of them they would have been good to go...........

[Nessism]

Measure the bore for wear. The manual provided instructions. If the bore is within the service limit, hone and install new rings. If out of spec, bore it.

[froldt]

No need to get oversized pistons just because your pulling the block. When you pull the block, take it to a machine shop and they can measure it to see if its within spec. It may be fine. Put in new rings (with proper gap of course), hone it, and you're good to go.

My cylinders were in great shape when I pulled my block off. Except for a huge scratch in one of them they would have been good to go...........

Do I have to remove the pistons to clean them? (I know I don't to get the new rings on there.) If I do that, then will I need new clips and pins?

Measure the bore for wear. The manual provided instructions. If the bore is within the service limit, hone and install new rings. If out of spec, bore it.

Unfortunately, I don't have anything to measure the bore with. I'll just have to let the machine shop do it, I suppose.


I need to drop the jugs off at that machine shop for them to check out, and get to ordering the necessary parts.

[DimitriT]

Use feeler gauge to measure the ring end gap (take the top ring off of a piston and insert it near the top of the of the cylinder - the gap is the space between the ends of the ring). Compare ring end gap along several places in the cylinder. I believe the service limit is 0.3 mm. If the gap is the same up and down the cylinders, you are probably ok with just new rings and hone.

I had to pull the head on the 550 recently. I measured a gap of 0.10 and didn't even bother putting in new rings. The compression is better than 130 psi for all cylinders.

I'm not sure what you got for the "valve job". New valves? New seats? Did you try just adjusting clearance and checking compression? In some cases, the problem you describe is due to valves needing adjustment and not a top end overhaul.

I suggest you get a Clymer's 750 manual. Everything you need is in that manual and in this forum.

As far as gaskets, look for the Vesrah set. I think www.crc2onlinecatalog.com has them.

[mark]

Do I have to remove the pistons to clean them? (I know I don't to get the new rings on there.) If I do that, then will I need new clips and pins?

If you're pulling the head, you're probably going to have to pull the block. Pistons wouldn't need to be removed to be cleaned.

If you do take the pistons off, you MUST use new clips, if you can feel wear on the pins I would replace them (about $5.00 a piece).

Be careful removing your pins, if that is what you decide to do. You can tap them gently, but don't use much force. Sometimes they don't want to come out very easily in which case you'll have to make or buy/borrow a pin pulling tool. Don't bang away at them you could do expensive damage.

[froldt]

I'm not sure what you got for the "valve job". New valves? New seats? Did you try just adjusting clearance and checking compression? In some cases, the problem you describe is due to valves needing adjustment and not a top end overhaul.

I suggest you get a Clymer's 750 manual. Everything you need is in that manual and in this forum.

As far as gaskets, look for the Vesrah set. I think www.crc2onlinecatalog.com has them.

Thanks for the info. I believe the machine shop refaced the valves and seats. First I adjusted the clearance, and the compression was horrible (didn't even register on #4). The machine shop said that the valves were pitted, but not so bad that they needed replaced.

I've got a manual, apparently I'm just reading it wrong. I read it as if I needed to remove the pistons (which made me assume I'd need new clips/pins). It does mention soaking the pistons in some sort of cleaning solution (don't remember what off-hand), so I was checking before I went and ordered too much/not enough.

thanks for the info!