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hard chrome liners

sixpack

Forum Website User
Non-VOC Member
good day to all---per 1950 rapide i recently pulled off the top end to investigate a possible reason for excessive crank case pressure----to my surprise i found the standard bore liners to have been hard chromed with staggered pot marks on the walls of the liner from top top bottom-----when purchased the bike came with a recite from Conway Motors dated 1955 for complete Lightning package---my question to you ---can anyone ID the process that was performed on these cylinders if so was it good or bad-----im thinking this is a contributor to the problem---can,t see how the rings can effectively seal----can provide pics---please help
 

Albervin

Well Known and Active Forum Website User
VOC Member
Do you have good compression on both cylinders? If you do then it would seem all is well at the top end. Usually chrome bore dictates different piston rings to standard bore otherwise you get rapid ring wear and loss of compression and all the associated problems. What sort of breather(s) do you have? Just because you have a receipt from 1955 doesn't necessarily mean that what you have now inside the bike bears any resemblance to what was done by Conways .... (12:1 compression, 32 mm intake, 10TT9 carbs, KVFTT magneto etc.) Good luck and keep asking questions.
 

sixpack

Forum Website User
Non-VOC Member
thanks for the reply---it still has the KVFTT #108----32mm intake with concentric, s ----haven't ID the pistons yet---still running a timed breather with larger 5/8 in hose---as the tachometer drive spoils the option for a breather in the timing chest----there was some damage to the top ring land on the forward piston ----time for new pistons and rings---just not sure if the spotty chrome liner can be trusted for sizing my replacement parts----cheers
 

Black Flash

Well Known and Active Forum Website User
VOC Member
as far as I know the old aircooled 911 Porsches had those " dimpled" hardchrome liners fitted. I would not be surprised if these Porsche parts including special pistons for that liners made by Mahle found their way into this special design. You can still buy piston blanks of Mahle ( I think the minimum was a set of 4).
now that German car industry is producing flat out again, it may be that they are reluctant selling small order piston blanks though.
 

sixpack

Forum Website User
Non-VOC Member
good day to you B-Flash----Specialloid e7/9 currently live in the beast now--your input makes me feel better about reusing my liners with maybe a 100 grit pass as they measured clean for tapper ---same piston knurled to take up the 1thou over spec condition ---and im guessing an iron ring set to achieve proper break in ---many thanks
 

davidd

Well Known and Active Forum Website User
VOC Member
My experience with Nicasil is that the pistons and rings wear out while the bores remain in good shape. I know tuners that believe the bores should be highly polished 1500 to 2000 grit as a finish -- with new rings and pistons they get leak down test that are close to 0%. I have not done that. I used a flex hone that was reccomended and it was 280 grit. I subsequently used a hone that was sent by the company that did the Nicasil coating and honing and it was much gentler, probably 500 to 600 grit. The goal is to avoid piercing the surface coating.

What I took away from this was that the rings will bed on a highly polished bore if the rings are new and the correct type for the material and the bore not glazed and in decent shape. You can use a lower grit as I did, but the swarf from the rings will be much greater (which did not bother me this time.)

I would have done a leakdown test to see where the extra cankcase pressure was coming from. Short of that, If you are runing specialoids, I assume that they are worn out, but only measuring will tell. It sounds like the ring grooves may be worn out. The racing pistons I use initially showed distress due to overheating. This was cured by moving the top ring down further away from the crown and ceramic coating. I do not think much of knurling, but it is probably fine if you are not going to run the bike much. I would not run a knurled piston. The timed breather works fine if it is timed properly, but its use has fallen out of favor. I can send you some articles on the breather if you contact me at daviddunfey@aol.com.

Good luck,

David
 

mercurycrest

Well Known and Active Forum Website User
VOC Member
Hi Sixpack,
I'm with David's opinions on the breather and not knurling your pistons. I would consider the overall condition of the motor and if it seems to be a low mileage engine in decent shape, just freshen it up with new rings and sealed intake guides. You said the piston clearances were .001 over spec., does that mean they're .006 or so? should be fine, Racing clearances were around .010 and up on these engines. On a Morgan Trike with a Matchless or JAP you'll find .014-.015 clearances, even today! Personally, I feel a bit more secure with "looser" clearances. Keep in mind Ron Kemp (as good a Vincent builder as there is) stuck his low clearance pistons equipped Vincent after about 100 miles on I-5 when he brought it to the States. This ain't Jolly Old England.
Cheers, John
 

Black Flash

Well Known and Active Forum Website User
VOC Member
the dimples were an old design thought by Porsche engineers to keep oil on the hardchrome liner wall. this was especially necessary on high power aircooled Porsche engines. with standard liners the wear on these engines was too much and the chromed liners worked very well indeed, whitout the dimples the engines seized alot.
My bored and stroked Bob Dunn engine has an nicasil plated alloy liner fitted, the heat transfer of that compared to an iron liner has increased tremendously. touching the barrel after only a few minutes of idling is a painfull experience. After many years of modifications Bob is totally convinced using thes liners for his highly tunes engines. the same applies to the standart breather.
if the engine is in good mechanical condition and the breather correctly timed there should be no issues. Bob recommends the slot being 0.375" wide. I have just machines a new sleeve yesterday keeping the outer diameter as thin as possible to enable as much room for air in the tubular compartment around that sleeve on a Comet engine. I am at the moment doing the wiring but have to go on holiday ( the better half story, you know that?) on saturday. so the next three weeks there will be no progress. If only we could have holidays at home.....
Bernd
 

sixpack

Forum Website User
Non-VOC Member
My experience with Nicasil is that the pistons and rings wear out while the bores remain in good shape. I know tuners that believe the bores should be highly polished 1500 to 2000 grit as a finish -- with new rings and pistons they get leak down test that are close to 0%. I have not done that. I used a flex hone that was reccomended and it was 280 grit. I subsequently used a hone that was sent by the company that did the Nicasil coating and honing and it was much gentler, probably 500 to 600 grit. The goal is to avoid piercing the surface coating.

What I took away from this was that the rings will bed on a highly polished bore if the rings are new and the correct type for the material and the bore not glazed and in decent shape. You can use a lower grit as I did, but the swarf from the rings will be much greater (which did not bother me this time.)

I would have done a leakdown test to see where the extra cankcase pressure was coming from. Short of that, If you are runing specialoids, I assume that they are worn out, but only measuring will tell. It sounds like the ring grooves may be worn out. The racing pistons I use initially showed distress due to overheating. This was cured by moving the top ring down further away from the crown and ceramic coating. I do not think much of knurling, but it is probably fine if you are not going to run the bike much. I would not run a knurled piston. The timed breather works fine if it is timed properly, but its use has fallen out of favor. I can send you some articles on the breather if you contact me at daviddunfey@aol.com.

Good luck,

David
good info ----many thanks
 

sixpack

Forum Website User
Non-VOC Member
My experience with Nicasil is that the pistons and rings wear out while the bores remain in good shape. I know tuners that believe the bores should be highly polished 1500 to 2000 grit as a finish -- with new rings and pistons they get leak down test that are close to 0%. I have not done that. I used a flex hone that was reccomended and it was 280 grit. I subsequently used a hone that was sent by the company that did the Nicasil coating and honing and it was much gentler, probably 500 to 600 grit. The goal is to avoid piercing the surface coating.

What I took away from this was that the rings will bed on a highly polished bore if the rings are new and the correct type for the material and the bore not glazed and in decent shape. You can use a lower grit as I did, but the swarf from the rings will be much greater (which did not bother me this time.)

I would have done a leakdown test to see where the extra cankcase pressure was coming from. Short of that, If you are runing specialoids, I assume that they are worn out, but only measuring will tell. It sounds like the ring grooves may be worn out. The racing pistons I use initially showed distress due to overheating. This was cured by moving the top ring down further away from the crown and ceramic coating. I do not think much of knurling, but it is probably fine if you are not going to run the bike much. I would not run a knurled piston. The timed breather works fine if it is timed properly, but its use has fallen out of favor. I can send you some articles on the breather if you contact me at daviddunfey@aol.com.

Good luck,

David
lots of good info-----thanks
 
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