Bike won't idle, poor compression.

[the quinner]

[quote="Krauser4valve"]I'm holding the stock R100 piston, the Krauser piston I am using and the spare Krauser piston (for a Nikasil bore, low compression, which I found in a box the other day. Now I know where the too-small rings came from) in my hands. The Krauser piston has smaller top ring land, .055 inches versus .068 for the stocker. I also have the stocker top ring and the Krauser is 1.5mm thick versus the 1.75mm for the BMW part.

All three rings had the same .048 inch gap. New rings, a sweet .015

My bad...I checked a set of pistons and you are very correct. The difference is the top ring (Krauser = 1.5mm, stock KS pistons=1.75mm). BUT, I'm a little confused. You mentioned (1) that your piston had 94.20 stamped in the top. 94.20mm would be a first oversize for the Mahle forged pistons. The only "B" sized pistons that Krauser had made were stamped 93.96 and were intended for "B" sized Nikasil cylinders. (2) The rings you link to say they are for "94mm bore"...and you say they give you a nice end gap of 0.015". (3) you said that the cylinder was within the "B" bore range...but you said that was a bit of a guess. I suggest finding someone with some basic cylinder/piston measuring tools and figuring out what you have...some things aren't adding up...


That's interesting info about the plugs, need to definitely check that out. I got the last few sets from a guy on Ebay and I still have a few spares. The Triumph TSS used them too. The NGK plugs don't look shrouded, maybe I'll upload a picture so that you guys can take a look.


The metal "body" of the Champion plugs is a bit longer than the NGKs. I'm talking about the part between the threads and the hex nut. With the NGKs, the hex part bottoms out before the gasket surface reaches its seaing surface. If I recall correctly, the Champions protrude about 2mm farther into the combustion chamber than the NGKs without the modifications.

IIRC, they were .30 thick, have to dig them out, maybe they were there to correct what seems to me to be a very offset contact point on the valve stem. The valves don't seem to have been touched on the tip, but I don't have any specs for them to be matched to. CC did some port matching on the castings, nothing too crazy.


They were very rough out of the box and required some port matching and cleaning

This is worth repeating:

Since you have one head off the bike, I strongly recommend disassembling everything for a thorough inspection. Krauser heads are known for going through guides...based on the piston ring, I would want to double and triple check everything that was done or that could be a problem. I sure don't have all the information, but the story, as told, doesn't give me a lot of confidence that the job was done correctly the first time. If it were me, I'd want to strip both sides for a thorough inspection and careful reassembly.

[Krauser4valve]

"You mentioned (1) that your piston had 94.20 stamped in the top. 94.20mm would be a first oversize for the Mahle forged pistons. The only "B" sized pistons that Krauser had made were stamped 93.96 and were intended for "B" sized Nikasil cylinders. (2) The rings you link to say they are for "94mm bore"...and you say they give you a nice end gap of 0.015". (3) you said that the cylinder was within the "B" bore range...but you said that was a bit of a guess. I suggest finding someone with some basic cylinder/piston measuring tools and figuring out what you have...some things aren't adding up..."

I should have corrected that posting at some point, the cylinder have a 'B' stamp on them but they have been overbored to the first oversize. I dug out a set of bore gauges and a 4" mic and checked the sizing, no taper and the piston clearance is correct. A quick pass with a Flex-hone and I have a good scratch-pattern, but I'm stalled there as the second-floor tub decided that it was headed to the basement (maybe the heat?) and I need to address that first.
Any recommendations on a valve compressor? Or the valve length? Thanks again.

[Chuey]

Can I join in with some questions on Krauser heads? I have a pair of them on a 1978 R100. I want to use mine on a later model engine I've bought for that purpose. Changing from the '78 cylinders to the Nikasil cylinders, as I understand it, will be the part of the job I need to buy parts for.

What parts will I need in order to use the Nikasil cylinders? I've been told the pistons are different and I assume that if I buy the correct pistons for the update, they will have the correct rings. If the pistons are the same from older cylinders to Nikasil, and only rings are needed, I'd like to know that as well.

Chuey

[the quinner]

I should have corrected that posting at some point, the cylinder have a 'B' stamp on them but they have been overbored to the first oversize. I dug out a set of bore gauges and a 4" mic and checked the sizing, no taper and the piston clearance is correct. A quick pass with a Flex-hone and I have a good scratch-pattern, but I'm stalled there as the second-floor tub decided that it was headed to the basement (maybe the heat?) and I need to address that first.
Any recommendations on a valve compressor? Or the valve length? Thanks again.

Yes...get the tub out of the basement first...the bike will wait patiently...

Okay, you're first oversize in iron barrels. Are the rings oversized? Or, were they intended to be filed to size (rare in today's world)? I guess the engine was built with oversized pistons, oversized cylinders...and standard rings?

As far as a valve spring compressor...I use an OTC 4572...about $50 plus shipping online (find an engine shop that might loan or rent one to you?). Valve length? not sure...I'll see if I can get you a ballpark number later today.

[the quinner]

Can I join in with some questions on Krauser heads? I have a pair of them on a 1978 R100. I want to use mine on a later model engine I've bought for that purpose. Changing from the '78 cylinders to the Nikasil cylinders, as I understand it, will be the part of the job I need to buy parts for.

What parts will I need in order to use the Nikasil cylinders? I've been told the pistons are different and I assume that if I buy the correct pistons for the update, they will have the correct rings. If the pistons are the same from older cylinders to Nikasil, and only rings are needed, I'd like to know that as well.

Chuey

Chuey, the pistons are fundamentally similar...a high quality, forged Mahle piston. The original kits were offered for (1) 1980 and earlier and (2) 1981 and later. The 'early" kits came with a first oversized piston with a chrome top ring...the "later" kits came with a standard sized piston with a cast iron top ring. Each kit was originally available in "A", "B" and "C" sizing. (note: because they are forged pistons, the actual size is a hair smaller than the corresponding stock cast piston)...

So...if your 1978 cylinders are the originals...and they were bored and fit with the Krauser "iron" pistons...they will not fit into the smaller (i.e., non-oversized) bore of the Nikasil cylinders. If you call Eurotech or De Hobbyist, I think they will tell you that they only have "C" sized pistons for the Nikasil cylinders. I have a friend who has been searching for "C" Nikasil cylinders for quite some time...apparantly, they are hard to find. He's on the verge of sending the pistons and cylinders out to be replated to a "C" spec.

First, see what you have. Anything is possible, so start there.

If what you have fits a Nikasil barrel appropriately, then just get the proper rings. If you have the oversized pistons, you will need pistons and rings.

You still running the bike shop? I might swing by in mid/late July.

[Krauser4valve]

Okay, you're first oversize in iron barrels. Are the rings oversized? Or, were they intended to be filed to size (rare in today's world)? I guess the engine was built with oversized pistons, oversized cylinders...and standard rings?

As far as a valve spring compressor...I use an OTC 4572...about $50 plus shipping online (find an engine shop that might loan or rent one to you?). Valve length? not sure...I'll see if I can get you a ballpark number later today.[/quote]
The rings that WERE on it I am guessing came from a set of pistons that I never knew I had, the builder must have acquired them from somewhere. They were inside one of my old cylinder barrels that were too rust pitted to use, covered in grease for protection. They are marked "93.95" on the top, with a hand-engraver, and are apparently fly-cut to lower the compression. Underneath you see the Mahle logo, "94L10" and "CO21". The top ring is chrome btw.
The ring set I have now are for the .10 over pistons, Deve's out in Vegas made them, nice people to deal with.

[Krauser4valve]

Can I join in with some questions on Krauser heads? I have a pair of them on a 1978 R100. I want to use mine on a later model engine I've bought for that purpose. Changing from the '78 cylinders to the Nikasil cylinders, as I understand it, will be the part of the job I need to buy parts for.

What parts will I need in order to use the Nikasil cylinders? I've been told the pistons are different and I assume that if I buy the correct pistons for the update, they will have the correct rings. If the pistons are the same from older cylinders to Nikasil, and only rings are needed, I'd like to know that as well.

Chuey

Chuey, the pistons are fundamentally similar...a high quality, forged Mahle piston. The original kits were offered for (1) 1980 and earlier and (2) 1981 and later. The 'early" kits came with a first oversized piston with a chrome top ring...the "later" kits came with a standard sized piston with a cast iron top ring. Each kit was originally available in "A", "B" and "C" sizing. (note: because they are forged pistons, the actual size is a hair smaller than the corresponding stock cast piston)...

So...if your 1978 cylinders are the originals...and they were bored and fit with the Krauser "iron" pistons...they will not fit into the smaller (i.e., non-oversized) bore of the Nikasil cylinders. If you call Eurotech or De Hobbyist, I think they will tell you that they only have "C" sized pistons for the Nikasil cylinders. I have a friend who has been searching for "C" Nikasil cylinders for quite some time...apparantly, they are hard to find. He's on the verge of sending the pistons and cylinders out to be replated to a "C" spec.

First, see what you have. Anything is possible, so start there.

If what you have fits a Nikasil barrel appropriately, then just get the proper rings. If you have the oversized pistons, you will need pistons and rings.

You still running the bike shop? I might swing by in mid/late July.

Can he use the pistons I mentioned above? I sure don't need them...

[Chuey]

You still running the bike shop? I might swing by in mid/late July.

Yes, I still have the shop and work there every day except Sunday and Monday. Your visit will be welcome.

Chuey

[Krauser4valve]

Back to work putting the engine back together, have one cylinder done after spending the summer re-assembling a crumbling bathroom. The previous builder had added a compression-lowering shim, then to compensate for effectively lengthening the cylinder added lash caps to the valve stems. I got rid of that mess and for the first time the lash adjustment is within the correct range.

I plan on putting the left side back together today, just a quick honing for the new, correctly gapped ringset that Deves made up for me. Anyone have any thoughts on what the static timing should be on these engines? The manual has nothing to add on the matter.

[Chuey]

Chuey, the pistons are fundamentally similar...a high quality, forged Mahle piston. The original kits were offered for (1) 1980 and earlier and (2) 1981 and later. The 'early" kits came with a first oversized piston with a chrome top ring...the "later" kits came with a standard sized piston with a cast iron top ring. Each kit was originally available in "A", "B" and "C" sizing. (note: because they are forged pistons, the actual size is a hair smaller than the corresponding stock cast piston)...

So...if your 1978 cylinders are the originals...and they were bored and fit with the Krauser "iron" pistons...they will not fit into the smaller (i.e., non-oversized) bore of the Nikasil cylinders. If you call Eurotech or De Hobbyist, I think they will tell you that they only have "C" sized pistons for the Nikasil cylinders. I have a friend who has been searching for "C" Nikasil cylinders for quite some time...apparantly, they are hard to find. He's on the verge of sending the pistons and cylinders out to be replated to a "C" spec.

First, see what you have. Anything is possible, so start there.

If what you have fits a Nikasil barrel appropriately, then just get the proper rings. If you have the oversized pistons, you will need pistons and rings.

Excuse my ignorance on this matter, but could a C size piston be chucked up into a lathe and turned down? Then you could have some of the new space age coatings applied and use it in the stock size Nikasil cylinders, no?

Chuey