Topic: Diagnosing newly-rebuilt top end / rings / cylinders

[bwaller]

The best way to measure this of course is with accurate instruments. If this wasn't a fresh rebore I'd suggest you get a machine shop do it for you. They can measure for taper etc.

Using a feeler gauge is ok unless the bore is already well used, but seeing you've already been down this road better do it right this time.

For your entertainment install the piston with a feeler gauge together(proper orientation) into the bore from the bottom. Then with one hand hold the piston and the other pull the feeler out. Start with a thin feeler and you'll have an idea how thick to use. Don't force the piston in with "too thick" a feeler. The very bottom of the sleeve will be the least worn, 1/2"to 1" down from the top the greatest wear.

You can install the piston in either orientation but you want to measure the clearance at the bottom of the (middle of) the piston skirt (perpendicular to the pin) where the piston is largest.

Clear as mud? 

[iron_worker]

FYI: I used Cycle X valve guides, seals, springs, and valves ... not oil burning issues here!

IW

[flybox1]

Only possibility is that the CycleX-supplied green valve seals are crap and I need new ones.

OEM valve seals!
....highly recommended by many of the F'ers here 

[grcamna2]

flybox1,
I just noticed your new Avatar,who's that in it and what's he doing ?

[flybox1]

flybox1,
I just noticed your new Avatar,who's that in it and what's he doing ?

That's my youngest son, Matt.  He's my cover mechanic.  He's a pro with the allen caps.
If i'm in the garage, so is he...

[grcamna2]

Great Legacy     

[MRieck]

I can have a cylinder bored/honed for much less than 350.00 and guarantee the fit. I have have many, many cylinders bored for people on the forum....never any problems.

[bwaller]

There's this guy Mike that has close ties to a great shop. 

I was going to suggest you but thought it wise to clear it with you first. I didn't realise you looked after this for folks, well done.

[grcamna2]

I can have a cylinder bored/honed for much less than 350.00 and guarantee the fit. I have have many, many cylinders bored for people on the forum....never any problems.

Go for it wohali ! 

[MRieck]

There's this guy Mike that has close ties to a great shop. 

I was going to suggest you but thought it wise to clear it with you first. I didn't realise you looked after this for folks, well done.

You are all part of my flock Brent.

[grcamna2]

There's this guy Mike that has close ties to a great shop. 

I was going to suggest you but thought it wise to clear it with you first. I didn't realise you looked after this for folks, well done.

You are all part of my flock Brent.

 

[wohali]

@MReick Sounds nice, but won't shipping from Toronto be prohibitively expensive? Send me a PM and I'll go get shipping estimates.

[ekpent]

Are you sure its a piston/bore issue and not just a problem with those custom rings you had made ? Could just need a simple ring set and a light hone. You said proper rings for that model are now available I believe ?

[wohali]

I'm not sure, no. I will be heading out to the shop in a few minutes to do feeler gauge measurements, and if those are inconclusive, get out the mic + telescoping gauges and attempt more measurements.

[ekpent]

I'm not sure, no. I will be heading out to the shop in a few minutes to do feeler gauge measurements, and if those are inconclusive, get out the mic + telescoping gauges and attempt more measurements.

If its just the crap rings you will save a lot of money just getting the proper ones. Have you checked with the other person who bought a set of the custom built to see if they have run them yet ?

[bwaller]

I'm still not sure what you did last time. Hone & those rings only?

[wohali]

Hone and those rings only.

I'm back from the shop. I tried a few things:

• Mic'd the pistons, they're reading 60.97 or thereabouts at the widest part of the skirt perpendicular to the pin. This seems in spec per the Honda service manual. For the remainder of the tests, I used piston #1, as I've only removed the rings from that piston.
  
• I set a telescoping bore gauge to 61.00mm, applied 3-in-1 oil and used it to "rotate through" perpendicular on both X and Y axes in the bore. For vertical reference, I used a 90-degree t-square sitting matched with the top of the cylinders. Except on #2, this was very difficult to do - basically impossible - and on #2 it was barely possible.
  
• A couple of "direct" telescoping bore gauge measurements (loosen the gauge, put the gauge perpendicular about 0.5" down from the top of the cylinder, rock back and forth a few times to ensure the gauge has "set up" correctly, set the lock, remove from cylinder, mic the gauge). These never measured over 61.01mm. The mic's resolution is 0.01mm.
  
• The feeler gauge approach outlined by bwaller above. On all of the cylinders I could fit only my smallest 0.002" feeler gauge in alongside the widest part of the piston, and remove it with a few pounds of force (no scratching/forcing). On #2 I was able to remove the 0.002" gauge almost freely, but a 0.003" gauge would stick like the 0.002" one would on the other cylinders.
  
• The MReick "drop test". Put the cylinders right side up on top of a piece of cardboard. Put a piston into the cylinder and drop it. In all cases the piston didn't fall instantly; there was a little bit of an air cushion resisting its motion -- but not much.
  
• Turn the cylinders sideways, put the piston in and look for light around the outside of the piston. I was able to see around the outside of the piston on the top (the side away from Mama Earth) on all 4 cylinders.
  
• Inspected the rings again. All 3 rings show absolutely no markings for top or bottom, even under a magnifying glass - the profiles are perfectly symmetrical. The Total Seal oil rings are one-piece jobbies.
  
• Gapped the rings on Piston #1. All 3 rings were around 0.017".
• Re-examined the oil markings on my top cylinder gasket (picture here). There does appear to be more staining right around the cylinder than I originally expected, but when she was all together neither the head nor the cylinder gaskets ever leaked. All the oil that was lost was burning off and coming out the exhaust.
  

So if anything she's close on the tolerances, but probably a bit over / not perfectly round. I think my options are:

• Spend $80 + shipping + import tax on the factory rings + get new gaskets, reassemble and see what happens. If this doesn't work I'm out the $80 + probably another couple of gaskets.
• Spend $60 to bring it to someone for checking and honing locally. I could do this + the $80 above if it measures out OK, if we suspect the rings.
• Just go 836cc ($500 for the pistons + shipping + tax), do the rebore locally or MReick or whomever, + gaskets + reassembly

[Jerry Rxman Griffin aka MuthaF'er]

1 piece oil rings? proper end gap?

836 kit for $120 on ebay. Have it shipped to Mike and maybe even a set of cylinders sourced cheaply shipped to Mike.

I know Mike doesn't mind 

[wohali]

Is that an 836 F2/F3 kit though? Regular 836 kit will have the wrong CR.

I don't know if the cylinders are different between F2/F3 and other model years. At the very least I'll need to paint them black.

And yes, 1-piece oil rings, and "Gapped the rings on Piston #1. All 3 rings were around 0.017" which is within spec per the service manual.

[grcamna2]

If it was mine I'd do 1mm or more over-bore and piston kits w/ 3 piece oil rings.
Jerry has an idea about some cylinders sourced locally to MRieck... then you'd only have shipping to you. Mike may have an idea,PM him. 

[Jerry Rxman Griffin aka MuthaF'er]

The $120 kit is NOT F2/F3.

The F2/F3 cylinders have a different part number.

Yeah, thats what I did when I got my APE 1000 kit, I bought EBay cylinders and had them shipped directly to Big Jay. That would save you cross border BS. We probably have many guys that could sell and ship to Mike.

Many old school guys still like 1 piece oil rings. I prefer 3 piece. Doesn't leave that direct path through. May be minor but it's there.

Do you feel you had a good hone and your rings seated well or perhaps you babied it too much and the rings didn't seat properly?? Ahhh, the unanswerable questions...

[grcamna2]

wohali, When you find another 'F' cyl. block,you could sell your present cyls./pistons/rings later to recoup some needed $ if you desired to.

[wohali]

Hone was home done - it was probably just "OK." I have an embarrassing video of the process I can post if you really want to see it

Babied? So much oil was burning I couldn't get over about 6-7k, and without 5th gear I couldn't exceed about 45-50mph. (I just fixed that - 5th gear was on the shaft backwards. Oops.) I rode her at 45-50mph almost all the way from Toronto to Detroit and back with at least 2 other people from the forum here. There were points I accelerated faster to get on and off the highway but it was mostly that speed...I did my best not to hold a constant RPM but I also couldn't drop below highway speeds.

FYI I'm not especially worried about the cost (as I finally got employed again, yay!) But I'd like to keep the bike as stock as possible. Finding a full set of F pistons/rings/cyls in good enough shape to just install may be 6 months of waiting around. So I'd prefer to try something simpler - but I need help to know if putting the $80 rings on and getting a local hone job done is just a waste of time or not.

What's the biggest gap stock pistons + proper rings could manage, do you think? Hondaman's book says 0.0018" and if the feeler gauges are right, I'm already over that....and I'll have to bore / upsize the pistons anyway. Or perhaps I could get new cyl sleeves...not sure if this is something people actually do or not, though, it seems a bit over the top.

[bytio]

http://www.scheuerlein-motorentechnik.de/motorenersatzteile/motorrad/Honda/700-799-ccm-h7/CB750-F2--OHC-/kolbenkit-cb750f2-1-uem.html
Have a look at these, a little pricey but another option

[grcamna2]

Those are Good quality piston kits but kind of pricey.I've used Kolben Schmidt pistons on BMW 'Air Head' vintage 'R' engines and they Do last.