Repair, replace or accept?

Going through my 850 motor, it occurs to me that one of the most difficult things is deciding what level of wear to accept.
Obviously it would be best to go for the "as new" condition, replacing everything which has signs of wear, but for those of us on a limited toy budget, that's not possible.

If something is knackered and out of tolerance, then the decision is easy, but if the part is worn, but not so badly, it becomes more difficult.

A case in point - tonight I was cleaning the barrels before taking them to a friend to discuss whether they should be bored to +0.040, or if they could just be deglazed. I removed the cam followers (quite badly worn due to a chocolate cam) and I find that the cam follower tunnels are not as smooth as I would have expected.

I know that oversize followers are available, but I don't see a spec for how much wear is acceptable before the tunnels must be bored out. I could always play safe and get both the cylinders and the follower tunnels bored out, but I really dislike removing metal without good cause, plus it's always a problem trying to find someone reasonably local who can do this sort of work without cocking it up - not too many Nortons on the road here you see. I can probably get the followers refaced for half the cost of new ones as well, o that's another point to consider.

Then I looked at the head. One valve spindle is sufficiently loose that I could pull it out of the head by hand, 2 others can be turned with a screwdriver without much effort. One solution would be to use the spindle fixing kit from RGM, but I suspect I'm going to use a bit of bearing fit on reassembly instead.

The valve tips are slightly worn, but there is no leakage paste valves when I fit the combustion chamber with paraffin, so I think I'll keep them. The adjusters are nice allan key ones, but the tups are looking a bit bashed up. Once again, accept or replace?

Still, if it was easy, any fool could do it I suppose

/Steve.

Steve, I can't help thinking that you are one who aready knows what you are going to do. I fall into that catagory from time to time and it's nice to get some opinions to help manage the process.

I think you have also answered your own question. A. Repair, B. replace or C.accept? Answer D. all the above.

Enjoy your process, that's my favorite part.

I went through my 750 engine on a budget to get it back on the road. It runs great, but now I am hoping I made the right decisions.
There are some spots I would spend some additional $ now as an after thought.
Do it right and do it once. It will pay off in the long run.

I only replace what is going to lunch the motor. Especially big end bearings and mains if they are slack. Cylinder wear won't usually cause a blow-up - replace the rings.

Good point, but in my case, I want to use higher compression pistons. These are around £290, so it's a good thing to check the bore carefully before ordering.

I've been wondering about what happened in this engine. The inlet cam lobes were badly worn (2-3mm on the lobes), the drive side cam bush and camshaft bearing surface were very badly scored & worn (something like 0.5mm clearance!).

The main bearings look fine, no signs of other than normal wear on the inner races & the rollers.

The current plan is to replace the cam, probably get the followers reground (or replaced if the scoring is too deep), strip the crank to check the sludge trap & the big ends (the con rod nuts are proving difficult to remove, so I'm waiting on a 1/4W socket which will need grinding to fit on the rods). New big end bearings, then send the crank and associated whirly bits off to be balanced.

Cam chain to be replaced, probably grind some material off the rockers, Ti valve collars, alloy valve adjuster nuts + the existing valve adjusters, possibly new valve springs, depending on their condition.

I'll probably get the head skimmed, probably not 0.040 though. I want to use the 0,003 head gaskets from JS, and want to aim for a compression ration of around 10:1 or just over. This to depend on how much difference there is between the 2 combustion chambers though - I want to try to minimise any difference there.

I'll also do something to fit the XS reed valve breather directly on the crankcase rather than the timing cover.

Have not yet opened up the gearbox, so I don't know what needs to be done there yet.

Hopefully the result will be a reasonably well sorted, oil tight bike, with a bit more performance then a standard 850.

/Steve, the great optimist

Surely if you are fitting new performance pistons you would be better off with a rebore. Then there will be no worries for the future?

Ah, but if the bores are in good nick, why rebore?
That's the turning point you see. Hopefully I'll be able to get a precise measurement this weekend and decide from there.

I suppose thats the beauty of owning a classic.
Everyone has their own opinion. I think I would play safe, but a you say if you are able to examine to a point where you are happy with it....

I find it's always much easier to diagnose the condition of someone else's bike parts than it is to do your own!

SteveBorland said:

If something is knackered and out of tolerance, then the decision is easy, but if the part is worn, but not so badly, it becomes more difficult.



I removed the cam followers (quite badly worn due to a chocolate cam) and I find that the cam follower tunnels are not as smooth as I would have expected.







/Steve.

Click to expand...

The cam follower and associated tunnel wear has always made me wonder "why" too. My own bike and others I've worked on seem to always have more wear in this area (or score marks) than the rest of the engine condition would suggest and really "beat" engines don't seem to have all that much more in this area. They seem to "oil" pretty well. Is it the same phenomenon that causes Amal slide and body wear? Two like materials sliding on each other?

My cam followers & bores had scoring, rather deep/irregular. I reasoned that this was from accidental contamination, sand on the front of the head/cyl joint that fallen in during a head gasket change. I stoned the highs off the followers, polished the bores to remove the highs, seems to be fine 20,000 miles later. YMMV :mrgreen:

higher compression pistons, get the head skimmed AND use the 0.003 head gaskets from JS? I might pick one but for goodness sake, not all three. I am sure you want to be able to ride on down the road yet have that secret punch available when the urge can no longer be suppressed.

10:1 or just over compression, as stated, is just too darn much for a street 850 and can be a double edged sword. Your going for "slightly" better than stock performance. I think you need a balance, to achieve your goals, between the 3 C's, Cam Compression and Carburation.

Biscuit said:

SteveBorland said:

..........If something is knackered and out of tolerance, then the decision is easy, but if the part is worn, but not so badly, it becomes more difficult.
I removed the cam followers (quite badly worn due to a chocolate cam) and I find that the cam follower tunnels are not as smooth as I would have expected.........../Steve.

Click to expand...

The cam follower and associated tunnel wear has always made me wonder "why" too. My own bike and others I've worked on seem to always have more wear in this area (or score marks) than the rest of the engine condition would suggest and really "beat" engines don't seem to have all that much more in this area. They seem to "oil" pretty well. Is it the same phenomenon that causes Amal slide and body wear? Two like materials sliding on each other?

Click to expand...

I'm not sure why either but I was wondering if the wear in there makes this a good candidate for switching to the BSA style lifters? Then you would not need to bore them out oversize, and the "chocolate cam" needs to be replaced anyway, right.

Steve, all I'll say is try to remain objective. It is easy sometimes to fall into the trap of thinking "I'm on a budget, so X or Y is off the agenda"

What I am referring to of course is JS upgrades. Folk think I was "flash" doing what I did to mine, but the plain fact is that the cam was suspect, the followers and follower tunnels were shot, piston and bore sloppy. And I had already decided I felt uncomfortable using stock rods (I know they're strong, but I've broken one before).

So, JS parts were actually a very economical way of building my motor.

Its not quite as 'black and white' for you I know, but new OS followers are expensive, I imagine boring out the follower tunnels will not be cheap and will require a specialist to do it right. Then there's the cost of the cam and pistons...

I also learnt over the years that 'sods law' is real. If you build an engine with known suspect parts... They WILL fail...!

Jus' sayin' ...

pete.v said:

higher compression pistons, get the head skimmed AND use the 0.003 head gaskets from JS? I might pick one but for goodness sake, not all three. I am sure you want to be able to ride on down the road yet have that secret punch available when the urge can no longer be suppressed.

10:1 or just over compression, as stated, is just too darn much for a street 850 and can be a double edged sword. Your going for "slightly" better than stock performance. I think you need a balance, to achieve your goals, between the 3 C's, Cam Compression and Carburation.

Click to expand...

No need to get alarmed These are simply different ways of increasing the compression ratio. As I've said before, I don't like removing metal unless pessary, so hear skimming for me is more to remove any errors in the combustion chamber volumes, or uneven surfaces etc.

High compression pistons are more expensive than standard flat top ones, but raising the compression ratio will probably require valve pockets to get clearance 'twixt valve & piston. This is quite difficult for me to do with standard pistons, which is why I'm planning on the expensive ones.

Given that a standard gasket is around 0.040" thick, using a copper 0.020" or a JS 0.003" one is simply another parameter to choose to get the desired result.

If I were really sensible, I would probably do the head changes first then measure the CR wit the standard pistons and the 0.003" gaskets, and try that on the road, then pull it apart and put the lumpy pistons in.

The problem with this approach is that I don't think that a PW3 cam will work well without the new pistons. According to my calculations, with my 0.020 oversize bores, std pistons, untouched head and 0.003 gaskets, I will only get a CR of around 9:1. Skimming the head by 0.040 raises it to around 10:1, but I'm rather certain that this will require pockets in the piston.

Any decision / verdict / plan yet Steve?

I was talking to a friend of mine who is a fitter (works with building one off machines for the packing trade), and had a chat to Mick Hemmings yesterday.
Based on there input, I will (initially at least) leave the head as it is, other than flattening the surfaces.

Unfortunately, Mick does not have stocks of the high compression Wiseco pistons now - he says to go to Andover Norton who have taken over his stocks. Phil at A-N tells me that they do not currently have any, and I'm waiting to hear from them when they expect to get them.

So the current situation is that I more or less know what I want, but cannot get it :-(

Anybody have a set of 0.020 oversize high compression pistons in good nick lying in a box somewhere?

While I'm waiting though, I think I'm going to move my XS breather valve from the timing cover to the crankcase. Unfortunately there's not enough room to mount it directly as per Jim/CNW's rather neat valve, so I'm probably going to drill & tap a suitable hole in the crankcase and use a short length of threaded tube with a locknut plus a short length of tube to mount the valve. Not as elegant, but it solves the problem I think.

Latest news from A-N is that they did not get any oversize Wiseco pistons from Mick, and they do not know when they will have some.

Hmm, so either I go to Steve Maney (which involves boring out to +0.040), or I have to find someone who can skim the head, or I wait & see if A-N can deliver.
In the meantime I suppose I could go with the standard flat tops and the thin JS gaskets and see what happens.

I don't suppose anyone has a set of +0.020 O/S high compression pistons that they are not using?

/Steve.