Setting the timing properly

[chuck hahn]

unbolted and setting on the bench do cams go in normally?

[timebombprod]

Okay so the head is fine, tightened down without gasket and cams sit just fine, but these pistons do interfere with the valves, it's not the indented area where the valves go but on the sides of the pistons. I'll end up taking a video more than likely to show where they hit and all that but I was also thinking I could just get some gs750 pistons if I can't work this out as those are 65mm pistons.

[timebombprod]

https://youtu.be/dfmGPZAT40Y

https://youtube.com/shorts/6JZNCi_Es40?feature=share

[Suzukian]

The overhead cam is cast iron, if you try and bend it, it will crack for sure. Torquing the head down onto it really is the only way to get the cam straight again. The thing with steel/iron is that after it gets spinning, and hot, all lubed up, it will want to find it's center again. It will straighten itself out. I highly advise against bending it. It is very brittle and will crack on you.

[timebombprod]

The overhead cam is cast iron, if you try and bend it, it will crack for sure. Torquing the head down onto it really is the only way to get the cam straight again. The thing with steel/iron is that after it gets spinning, and hot, all lubed up, it will want to find it's center again. It will straighten itself out. I highly advise against bending it. It is very brittle and will crack on you.

Its fine, no bending, the issue now is that the pistons do hit the cylinder head, but it can be solved by dremmeling the surrounding areas.

[Suzukian]

I'm happy you found out what's going on. Your taking it off the pistons, not the head, right? It would be better if you could mill it off. Balance issues and what not, I wouldn't touch the top of the combustion chamber. You should weight each piston and make sure they weight the same.

It's always better to take your time and be ultra careful. It's not only time and money, but effort and experience, and the thrill when you go down on that much hotter bike that give you that incredible feeling when you riding on an engine you rebuilt. It's addictive. I've been lucky and have built a few, including a couple of Lycoming Engines(When I was training for an A&P license), 4.5 liter Mercedes V-8, a straight 6 dual overhead cam 280C Mercedes engine, and a few more bike engines. The feeling is addictive, makes you want to jump into another one.

[timebombprod]

Well the plan was to take off of the head as thinning the pistons would make them a much weaker area, I also learned that 750 pistons wouldn't fit properly either because of the layout in the 650 head,

what I'm going to have to check is if the spark plugs would interfere at all because it'd be a waste to dremmel out areas of the head only to find out the spark plugs interfere.

But yes, it'd be the head not the pistons, I've already asked about if it could cause an air pocket and make for an inefficient combustion. I don't know if I will start the process today and I might try to find other solutions, I could make my own gasket that is much thicker but I think the problem with that is since the valves don't interfere it would make it to where it's a lower compression going on.

[zed1015]

I could make my own gasket that is much thicker but I think the problem with that is since the valves don't interfere it would make it to where it's a lower compression going on.

With the pistons hitting the head you would summise that even with clearancing the chamber in that spot the piston may then hit elsewhere or the compression may be too high anyway and beyond that once you have a non contact situation between the piston and head you will then need to ensure you have the combustion chamber volume to achieve the correct compression ratio and sufficient valve to piston clearance which will most likely lead to the piston pockets needing relieving too.
What you should really do first is space up the head until the pistons clear the closest point of current contact by 1mm / 40 thou (This is the clearance you need to account for rod stretch etc at high rpm) and then fit a spacer or a base gasket of the same additional thickness to allow the head to be bolted down and the cams etc installed and timed.
Only then will you really see what's going on and be able to measure piston to valve clearances, combustion chamber volumes and clay the pistons etc so you can then make the correct alterations without blindly going from one problem to another.
Also how much was skimmed from the head ?
Are you sure it is the 'O' rings holding the head off the block and not the two location dowels at either side now being too long to allow the head to seat..

[Supercub]

Check mcmaster-carr for matching metric orings in buna-n rubber. Planing the head results in retarded can timing. Check the cam timing with a degree wheel. It's a study in itself but will save you from wondering later on. I found a great tutoral on it when I checked my CB160. It was 10 deg. retarded, set up by the markings but the pressed on sprocket had rotated off position.
if all else fails, return to stock!

[timebombprod]

if all else fails, return to stock!

Well I'd have to get another pair of cylinders lol as they are already bored out.

there's a note on the site saying that these are a different design so I think they are designed to have the head machined. We will see what happens, still thinking and deciding what I'll do aswell as taking measurements and such.

[Suzukian]

I would consider doubling, or tripling the cylinder base gasket(s) to get the clearance rather than messing with the combustion chamber. If you use Yamabond 3 4, they will never leak. You could do this dry. There is now way on any motor I have ever rebuilt that I would mess with the top of the combustion chamber, so much could go wrong, and it just may never run right. IMHO

[zed1015]

I would consider doubling, or tripling the cylinder base gasket(s) to get the clearance rather than messing with the combustion chamber.)

You really shouldn't stack fibre/paper base gaskets to gain the clearance as the tolerances will be inconsistent and alter when they are compressed.
The correct method is to use an aluminium block spacer which will accurately retain the required height adjustment.
The problem with this 740cc Cruizin Image kit (which they should stop selling) is well known as it uses GS750 pistons with hemispherical domes which don't match and interfere with the 650's bathtub/twin dome combustion chamber design.
See attached pics in this and the next post of the differing pistons.
The only solution is either machining and cc'ing of the combustion chamber, spacing of the barrel or a combination of both to achieve sufficient clearance and appropriate combustion chamber volume.
As stated in my previous post the block needs spacing 1mm / 40thou from the closest point of piston to head contact as a baseline before any other work is undertaken.
Once this is done you need to cc the cylinder at TDC to establish the combustion chamber volume and then calculate the current compression ratio to determine if any other or alternative work is needed.

650 PISTONS
You can see the reliefs either side of the dome that clear the squish band in the head.
s-l500 (1).jpg

[zed1015]

750 Piston.
Full hemi dome that hits the 650 squish area.


#s-l1600.jpg

[timebombprod]

That was my thinking aswell, if I put a larger gasket it'd be the easiest solution but then my compression ratio would presumably be lower as the spacing between the pistons and valves would be larger, and in a sense make this bore kit pointless.

The idea is to take out metal from the cylinder head itself, the way i plan to ensure that it is done properly is to put the cylinder head on the cylinder walls without the gasket, ensuring it can spin freely like that, and then i will know there is enough space once the gasket is back on.

The guy I mentioned before joe is the one who let me know to do it like this. And i guess if i take ojt to much ill just have to use some type of hardening compound to make up for the area lost.

[zed1015]

That was my thinking aswell, if I put a larger gasket it'd be the easiest solution but then my compression ratio would presumably be lower as the spacing between the pistons and valves would be larger, and in a sense make this bore kit pointless.

You cannot presume anything.
The pistons do not match the head and you have no idea of the compression ratio.
The distance between the valves and piston have no bearing on the compression ratio, it's the combustion chamber volume..
You cannot just fit a thicker gasket and cross your fingers.
Doing THAT really WILL make fitting the "big bore kit" pointless and you are likely to end up with a worse engine than you started with for all that wasted time and expense.
If you don't have the knowledge, skill or means to take the correct measurements and perform the appropriate modifications then you really should consider either handing the work over to someone who can or return it back to stock..