Soft Seize?

Beach · Sep 12, 2014

What should the ring gap be for these rings?

comnoz · Sep 12, 2014

Beach said:
What should the ring gap be for these rings?

About .017 inch would be a safe minimum. Jim

motorson · Oct 16, 2014

Just to follow up on this; Jim was correct in his analysis of the problem. Here are the pistons which I just got around to pulling out yesterday.

I noticed that the scuffing is to the outside of the engine on both sides and of course on the thrust side of the pistons. (rear-intake side)
Dan.

bill · Oct 16, 2014

GPM's ?

motorson said:
Just to follow up on this; Jim was correct in his analysis of the problem. Here are the pistons which I just got around to pulling out yesterday.

I noticed that the scuffing is to the outside of the engine on both sides and of course on the thrust side of the pistons. (rear-intake side)
Dan.

Hobot · Oct 16, 2014

very educational for me to see except not knowing if the rubbing was towards front or rear of piston pin. Also if possible can ya tell if the rubbing happened more in top or bottom of bore/stroke.

motorson · Oct 16, 2014

Hobot, I did say that the scuffing was to the rear of the wrist pin. It looks pretty even over the height of the piston. My bores are parallel so this one may not be too helpful in predicting how your tapered bores will do.
Cheers, Dan.

Hobot · Oct 16, 2014

Ok missed the wear side detail but we know that combustion stroke forces piston forwards in bore at top of stroke so I'm thinking it happened after BDC with crank pin lift flipping piston the other way near bottom of bore. At that's my rationalization to talk Canaga into barrel on floor tedious straddle dance he refused to video. Just run hack saw across the ridges for DIY piston knurling.

aceaceca · Oct 16, 2014

This has been discussed back in 2009. proper-piston-cylinder-clearance-t4860.html
I would question the use of 50w oil for a new engine.
My motto has always been to run em loose and slightly on the rich side.
General rule for water cooled v8 motors is .001 per inch of bore.
Just re ring it if bore wear is under .004.
This will give good service for another 50k or so miles.
My 2 cents worth for a penny.

motorson · Oct 29, 2014

Sad news on getting the cylinders bored out. I said .0045 thou and they wrote it down on the work order. I had talked to the service manager several times about the problem and said I needed a total clearance of 4.5 thousandths of an inch clearance. I just picked up my cylinders and just for grins put a piston in the bore out in the parking lot before driving home. It seemed a bit loose and on the way home I thought, "if he added .0025" to .0045" that would be .007"." And...sure enough, it is fitted to a feeler gauge tested .007" clearance!! Wow, now what to do? I have another cylinder I can have these pistons fitted to but I was going to put it together and ride.

concours · Oct 29, 2014

motorson said:
Sad news on getting the cylinders bored out. I said .0045 thou and they wrote it down on the work order. I had talked to the service manager several times about the problem and said I needed a total clearance of 4.5 thousandths of an inch clearance. I just picked up my cylinders and just for grins put a piston in the bore out in the parking lot before driving home. It seemed a bit loose and on the way home I thought, "if he added .0025" to .0045" that would be .007"." And...sure enough, it is fitted to a feeler gauge tested .007" clearance!! Wow, now what to do? I have another cylinder I can have these pistons fitted to but I was going to put it together and ride.

Happens all the time. Get a new machinist first.

Hobot · Oct 29, 2014

If ya just want to get some riding in and seek perfection later you can have the pistons knurled to take up the slight slack and get bit bigger ring set and make a proper gap and fly with the wind on noticed less friction for quick a while before knurls knocked down that even so may not be noticed. Worked a treat in Ms Peel. Older Hi end auto hot rod shops your best bet to find the equip to service or online.
https://www.google.com/?gws_rd=ssl#q=knurled+pistons

motorson · Oct 29, 2014

concours wrote:
Happens all the time. Get a new machinist first.

Yeah, that is what I was thinking too but I called them and the service manager expressed dismay and wants to see the whole cylinder with the pistons and everything and mentioned having to buy me a new set of pistons. I may let these guys try to make it right. The work actually looks real good and measures out parallel and round. He just missed the dimension by a country mile.
So, what to do? This shop has done good work for me before and I will come out with a good .040 over set up and an extra set of .020 over pistons and rings with only minor scuffing and 350 miles. I feel bad for them because the job only cost $100 and the piston set is worth $150. If I let them make it right and they do make it right it will go a long way to restoring my faith in good old down home American businesses.
Dan.

Nater_Potater · Oct 29, 2014

hobot said:
...have the pistons knurled to take up the slight slack and get bit bigger ring set and make a proper gap...

Yep, definitely an option. It's a bit of a double-edge sword, though. On one hand, you cover the piston with spiffy little oil reservoirs. On the other hand, you drastically reduce the amount of surface area the pistons use to transfer heat out to the jugs. For a street bike that sees only the occasional blast, you should be fine, but, as Steve mentions, they won't live as long a "proper" piston walls. 'Something to consider...

Nathan

concours · Oct 29, 2014

motorson said:
concours wrote:
Happens all the time. Get a new machinist first.

Click to expand...

Yeah, that is what I was thinking too but I called them and the service manager expressed dismay and wants to see the whole cylinder with the pistons and everything and mentioned having to buy me a new set of pistons. I may let these guys try to make it right. The work actually looks real good and measures out parallel and round. He just missed the dimension by a country mile.
So, what to do? This shop has done good work for me before and I will come out with a good .040 over set up and an extra set of .020 over pistons and rings with only minor scuffing and 350 miles. I feel bad for them because the job only cost $100 and the piston set is worth $150. If I let them make it right and they do make it right it will go a long way to restoring my faith in good old down home American businesses.
Dan.

Here's some previous discussion: norton-top-end-break-now-t14414.html

splatt · Oct 31, 2014

Why would you end up with +40's, the bores are obviously to small so the extra clearance would be honed out, new pistons of the same size fitted, doesn't need to be worn out any quicker. If you feel the workmanship was good give them the chance to put it right.

concours · Oct 31, 2014

splatt said:
Why would you end up with +40's, the bores are obviously to small so the extra clearance would be honed out, new pistons of the same size fitted, doesn't need to be worn out any quicker. If you feel the workmanship was good give them the chance to put it right.

Read the entire sad tale.. they are now too big. :cry:

motorson · Oct 31, 2014

Why would you end up with +40's, the bores are obviously to small so the extra clearance would be honed out, new pistons of the same size fitted, doesn't need to be worn out any quicker. If you feel the workmanship was good give them the chance to put it right.

It is because when I took the cylinders and pistons back to have it honed out only .002 to arrive at a total of .0045 clearance they actually honed it out more so that I now have a measured clearance of .010 which is more than double the desired clearance. This time giving them the opportunity to "make it right" will involve getting new .040 over pistons. They have offered to do this so we will see how it goes. The shop is Iron Horse Motorcycles in Monroe North Carolina in case anyone wants to know.

My main reason for letting them give this a try is that the guy said he wanted a .0025 clearance the first time and they were spot on that clearance. So, he can do it when he tries and they are just such nice people. I would feel super bad recommending against them if I didn't follow through and give them the chance they asked for. I figure that they will also know that a reputation is on the line if it doesn't go well this time around.

Dan.

splatt · Oct 31, 2014

I don't believe all is true, to hone 6 1/2 thou out will take a shit load of work, are you taken the clearance off the old seized pistons that will have shrunk and need to be tossed, max book size plus 20 thou and new piston should slip straight in, you need to refer to book size first, then check the piston size is correct, any piston that doesn't match book size shouldn't be used unless you know why it doesn't match and that reason isn't from damage

comnoz · Oct 31, 2014

splatt said:
I don't believe all is true, to hone 6 1/2 thou out will take a shit load of work, are you taken the clearance off the old seized pistons that will have shrunk and need to be tossed, max book size plus 20 thou and new piston should slip straight in, you need to refer to book size first, then check the piston size is correct, any piston that doesn't match book size shouldn't be used unless you know why it doesn't match and that reason isn't from damage

Not much work at all with a real hone. My Sunnen AN series straight hone will remove .010 in 2 to 3 minutes in my manual stroking machine with a 100 stone.
A real powerstroked honing machine can do it faster than that. Jim

I should specify that is from a Norton barrel. Now if it was a BSA barrel it would be a different story. Much tougher.

splatt · Oct 31, 2014

Not likely they are putting 100's in a finished bore is it, either going to be 200 or 300 to clean up seize marks, one thing I thought was strange was that it seized on only one side of the piston pin, it should have been pushing on both sides

Soft Seize?

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