Topic: Smoking Henry Abe 900 with broken stud - inputs are welcome!

[Henrik Vik]

Hi.
I've bought a CB750 F1, 1976, which came with a Henry Abe 900 kit in it. When I picked it up, the PO told me the bike was smoking, and he had given up on it. He had gotten the valves changed, as he thought the problem came from them. When he got the bike back from the garage after the valve change, and it was still smoking, he decided to sell it. But he had then concluded it was likely the smoke came from worn or broken piston rings, so he had gotten a set of new piston rings which he gave me with the bike. The bike had no visible oil leaks.

Once home, I fired the bike up without the exhaust on. Sure enough, excessive smoke came out of cylinder no. 1, on the far left side. It seemed to build gradually with the bike getting warm. I would describe the color as grey.

Yesterday I took the cylinder off. To my suprise the piston rings were all intact. The pistons and cylinder walls seems ok. The only thing I could say was different between the rings on no 1 from the others, was that the top piston ring was a bit dark /tanned at the opening of the ring. Which the others weren't. The pistons were all tanned on the top, as one would expect, but not overly black. The pistons are marked "Hainst 900 cc". They have three rings, the bottom an oil ring I guess.

Another thing I  found is that one of the cylinder studs was real loose at the base. It has been fixed with some sort of sement, and this is not holding it at all. I could move the stud sideways real easy. Not good.

So my questions are these:

1. Could the rings be broken or worn without me seeing it? I will still change them, I am just wondering.
2. If it is not the rings, what could cause the smoking?
3. How do I fasten the loose stud? I am going to order heavy duty studs, by the way.
4. Should I change the camchain? It is probably original.
5. The cam is marked "R9". Probably stock F1 cam. Should I change it to get more out of the 900 kit? The carbs look original too.

Thanks for any input

[Lars]

Usually the ring set comes with a mark on them telling you what is "up". #1 piston rings mounted wrong? Rings not moving freely?

When replacing the valves, did he replace the valve sealings? maybe the sealing on #1 is not properly attached?
(Take it there are sealings on the CB 750 like the CB 350/550).
Lars

[mick7504]

I you are pulling the motor down it would be a good idea to replace the rings if you have a new set at hand and deglaze the cylinder walls as well.
Worn valve guides are a strong possibility for the smoking issue.
Depending on how badly damaged the engine case is around the stud thread.
You can loctite a new stud in providing that there is enough undamaged thread to secure it properly.
A new cam chain is a good idea which means splitting the motor unless you use a link.
A different profile cam from stock in a big bore engine will make a noticeable difference.
Mick

[Jerry Rxman Griffin aka MuthaF'er]

1 piece oil rings? I have Total Seal part numbers posted for new rings with 3 piece oil rings IF you have the same pistons I have.

ring end gaps?

which Henry Abe pistons? 2 different sets made.

Heavy duty cam chain is about $30

R9 really doesn't tell anything. Put in a Megacycle 125-75.

Definitely check the valve guide clearance. The 77/78 F's are the ones that had the notorious problem but any model can have a problem. Valve seals hardened?

[Toxic]

Besides the valve stem seals and worn guides.

Take the barrels and pistons to a machinist and find out the exact measurements. Putting new rings in without finding out for sure if your barrels need an overbore is a waste of money.

You need the proper tools for this measurement and they are big time expensive.

You want an accurate measure of the cyl dia, top/ middle and bottom  and then the same measurements taken at 90 degrees to each other

-piston to cyl clearance as well.

Compare to stock figures to find out what you are looking at.

[Henrik Vik]

Rings are moving freely. There are three different rings in the new set. The oil ring I suppose is one piece? One ring with a spring inside? The other ring, the middle one I suppose, is different from one side to the other. Says top on one side, so that one is easy. The last one is the one to go at the top I guess. This one is the same on both sides. Does not say anything on either side.

If the new oil ring I have is one piece, will there be any need to replace them with 3 piece? If so, why?

Regarding the valves, I have no idea if he changed the valve seals or if the guides are worn. I will take them apart when I get a spring compressor. I guess this could be the culprit. I have new seals, and will change them. To check the guides I rock the valves about a bit? And if there is no sideways movement they are all good?

Thanks for the input on the megacycle cam. I will check it up.

[Jerry Rxman Griffin aka MuthaF'er]

I prefer 3 piece oil rings but some guys are just the opposite. My thought is the gap of 1 piece will allow more oil through rather than having 3 smaller gaps spaced apart. I tried 1 piece in my 810 kit once and got more smoking. I had Total Seal measure my H.A. 900 pistons for 3 piece rings and have info for all 3 replacement rings.

Are your pistons fully round by the wrist pins or are the sides by the wrist pins "indented" like mine? (for lack of appropriate term) 

I've never actually measured valves/guides. I sent my head to MRieck for some serious work and let the maestro do his magic.

[Henrik Vik]

Are your pistons fully round by the wrist pins or are the sides by the wrist pins "indented" like mine? (for lack of appropriate term) 

Mine are fully rounded. They are the same as the Hainst type A from the pics on this site

http://www.satanicmechanic.org/bigbore.shtml

[Henrik Vik]

R9 really doesn't tell anything. Put in a Megacycle 125-75.

I looked this one up. I am not looking for a serious race cam. I don't want to buy new pistons, springs, rods and the like. I just want to know if there is a moderate cam I should consider putting in, without changing a lot of other stuff. If not, could I expect any noticeable improvement over stock with only the 900 cylinder? Remember, everything else is stock. Carbs, head etc.

[mick7504]

A mid range cam would be good without going overboard.
This is from Cycle Exchange.
http://www.cyclexchange.net/Engine%20Parts%20Page.htm
There are some bolt in cams available that would add some spark and don't require any expensive modifications.
APE
http://cbrzone.com/sohc.html
Megacycle have similar profiles available as well.
http://www.megacyclecams.com/
Mick

[Henrik Vik]

Thanks for the input on the cams. I've also looked at Webcams 41 and 41a, which seems to be direct bolt ins as well.

But now I wonder if I have a more serious problem. I just checked the piston to cylinder gap. They are in the .004 range. Is this serious? Since I have the Henry Abe kit, I don't think I could get one oversize in these pistons. So what do you guys think? Is it still rideable? Will the rings take care of the slack. I dread to think of it's consequences. 

[mick7504]

It sounds like things are getting a bit untidy.
You won't get oversize HA pistons.
The block that you have would have been sleeved for the 900cc/67mm (888cc) pistons and it might be worth thinking about another block and boring that for an 836cc kit on the stock sleeves. (65mm)
While it's nice to have a handful of cubes in your motor, an 836cc set up properly will punch out some HP.
Mick

[Jerry Rxman Griffin aka MuthaF'er]

Henry recommended .001 to .0015 per inch of piston on my type B kit for street and larger for race. That works out to .003 to .0045. Loose but within HA's specs. I had mine done at APE recently and Jay used .002 I believe. 

Not sure if the rings for mine are the same as your's. I'd measure the ring end gap and go from there.

With everything else stock I'd consider some more duration to help fill up the larger bores. Most cams are direct bolt in as far as that goes but it's smart to degree them. When you get really big cams then you have to do some tricks. You'll gain bottom end grunt anyway with just the 900. A nice cam will cause your arms to stretch more at 5000+     

[Henrik Vik]

Henry recommended .001 to .0015 per inch of piston on my type B kit for street and larger for race. That works out to .003 to .0045. Loose but within HA's specs. I had mine done at APE recently and Jay used .002 I believe. 

Not sure if the rings for mine are the same as your's. I'd measure the ring end gap and go from there.

I measured the piston to cylinder clearance again. There is big difference in measurement between the top and the bottom of the piston. If I measure clearance at the top, I can actually get a .008 feeler in between. But measuring from the skirt/bottom I only get .0025. I hope this is good news. Won't the rings sort out the top clearance? And the bottom is what matters, in regard to piston slap? If so, maybe I'm all good?

I measured the piston ring gap:
top ring: .013
middle: .015
I didn't do the oil ring. I guess it is also within specs, since it's new as well.

Am I sorted? Should I open the champagne

[MCRider]

Henry recommended .001 to .0015 per inch of piston on my type B kit for street and larger for race. That works out to .003 to .0045. Loose but within HA's specs. I had mine done at APE recently and Jay used .002 I believe.  

Not sure if the rings for mine are the same as your's. I'd measure the ring end gap and go from there.

I measured the piston to cylinder clearance again. There is big difference in measurement between the top and the bottom of the piston. If I measure clearance at the top, I can actually get a .008 feeler in between. But measuring from the skirt/bottom I only get .0025. I hope this is good news. Won't the rings sort out the top clearance? And the bottom is what matters, in regard to piston slap? If so, maybe I'm all good?

I measured the piston ring gap:
top ring: .013
middle: .015
I didn't do the oil ring. I guess it is also within specs, since it's new as well.

Am I sorted? Should I open the champagne

In my limited knowledge base, the clearance between the part of the piston where the rings go and the cyl walls is not relevant. Only the skirt to wall. And you should measure the piston at its widest point is the pin boss. Perpindicular to the pin boss is narrower and will give you a false loose reading.

The piston is egg shaped to allow for uneven expansion. The cyl itself should be round.

Ring gaps are good at 13tou +/- 5, moslty plus, wouldn't want much tighter than 10thou I think.

Wait for confirm.

[Jerry Rxman Griffin aka MuthaF'er]

I have no input on your findings unfortunately. Maybe Big Jay (APE) or one of the builders can chime in. That's why I had him do mine. I don't have the measuring tools or any training on their use to correctly use them. I tried to find a legible copy of the HA info sheet on my computer but I could barely make out the one I found. I have an original somewhere if you need it but I'm out of town until saturday.