Author Topic: Need help with ID of RC piston application (Read 7638 times)

BPellerine · « **Reply #25 on:** August 19, 2013, 01:16:08 pm »

got my pistons today tews and they are just like yours except there are only three haha.strange that so little info on these rc knew these engines well and I cant help but think that his dealers would sell them without some warning.also the people who installed them back in the day would not all be happy if they did not know the specs.anyone got any old cycle world mags with info.any old dealers?bill

Big Jay · « **Reply #26 on:** August 19, 2013, 06:14:22 pm »

That is a cast 836. Those full dome pistons require the edge of the combustion chambers to be clearanced. That's why I never made mine like that.

Terry in Australia · « **Reply #27 on:** August 20, 2013, 01:03:51 am »

When I see Jay's posts, I think of him as Gandalf from "Lord of the Rings". Well, I suppose he is "Lord" of the Rings, and pistons, and cams, and cranks............

BPellerine · « **Reply #28 on:** August 20, 2013, 03:25:50 pm »

thanks so much Big Jay I did not think I would ever get the skinny on these.bill

754 · « **Reply #29 on:** August 23, 2013, 03:52:08 pm »

Just theory question here..but what if you were to machine the pistons as shown in my diagram.. Hope you can make it out..

Tews19 · « **Reply #30 on:** August 23, 2013, 04:01:36 pm »

Make the left pic look like right? I know I couldn't but my mom's husband said he can do anything with proper information provided
.. He is a cnc guy.... Shoot. Maybe you would like to experiment for me frank?

754 · « **Reply #31 on:** August 23, 2013, 04:10:34 pm »

Keep in mind if you do clearance a head.. Only About 100 thou or so will have to come off, if the chamber is close to bore size..

Terry in Australia · « **Reply #32 on:** August 23, 2013, 04:22:22 pm »

Quote from: 754 on August 23, 2013, 04:10:34 pm

Keep in mind if you do clearance a head.. Only About 100 thou or so will have to come off, if the chamber is close to bore size..

I think it'd be much safer to remove almost 3mm out of the combustion chambers, than from the top of cast pistons, that'd be a recipe for disaster...........

Medyo Bastos · « **Reply #33 on:** August 23, 2013, 04:28:02 pm »

i would have to agree.

i have 1 head clearanced to match 67mm pistons, and another out to 73mm

754 · « **Reply #34 on:** August 23, 2013, 04:30:45 pm »

Terry, how deep do you think the valve cutouts are?

Terry in Australia · « **Reply #35 on:** August 23, 2013, 04:42:35 pm »

I know what you're saying Frank, I just wouldn't risk it, those pistons are cast, and there's not 3mm's of spare material to remove from the crowns. Medyo has the right idea, and it's probably easier to mill out the combustion chambers anyway. Cheers, Terry.

Retro Rocket · « **Reply #36 on:** August 23, 2013, 04:58:01 pm »

Quote from: Terry in Australia on August 23, 2013, 04:42:35 pm

I know what you're saying Frank, I just wouldn't risk it, those pistons are cast, and there's not 3mm's of spare material to remove from the crowns. Medyo has the right idea, and it's probably easier to mill out the combustion chambers anyway. Cheers, Terry.

What about an F2 head, bigger combustion chamber...?

Terry in Australia · « **Reply #37 on:** August 23, 2013, 05:04:14 pm »

Yeah Mick, the combustion chambers are much deeper, but they need to be matched to the bore size, so if the cylinders are bored out to 65mm, the combustion chambers need to be "relieved", or milled out, to 65 mm for the first couple of mm.

Just trace the outline of the cylinders (using the new 836cc head gasket as a template) over the combustion chambers, and mill them out accordingly. Cheers, Terry.

Medyo Bastos · « **Reply #38 on:** August 23, 2013, 05:57:48 pm »

be sure to cc your combustion chambers before and after, as well as cc your piston crowns...

Tews19 · « **Reply #39 on:** August 23, 2013, 07:11:13 pm »

Holy #$%* you guys have a great deal of knowledge... How come I do not have any of you as my neighbors??? The pistons will be staying in my basement until I finish the 550 build. Then it's onto the 750 build..

BPellerine · « **Reply #40 on:** August 23, 2013, 09:02:09 pm »

thanks from me too guys I had asked Big Jay about this subject and he says the head is the place to take the meat off.I will have to wait until I get my head gasket to really see it.bill

PeWe · « **Reply #41 on:** August 24, 2013, 02:53:36 am »

Quote from: Tews19 on August 23, 2013, 07:11:13 pm

Holy #$%* you guys have a great deal of knowledge... How come I do not have any of you as my neighbors??? The pistons will be staying in my basement until I finish the 550 build. Then it's onto the 750 build..

Yes, you will learn a lot on this forum. Just search on various subjects or read the threads. I thought I knew most to know about my bike 20 years ago. I know much, much more know since reading the threads, asking questions here the last 3 years.

Big Jay · « **Reply #42 on:** August 24, 2013, 09:05:58 am »

Quote from: BPellerine on August 23, 2013, 09:02:09 pm

thanks from me too guys I had asked Big Jay about this subject and he says the head is the place to take the meat off.I will have to wait until I get my head gasket to really see it.bill

That is because Terry said there is no room to take it off the piston. I have not seen these pistons in person, so I don't know.

I made all of mine with a squish band machined into the piston so the head mod was not necessary. We even did our 1000s that way.

754 · « **Reply #43 on:** August 24, 2013, 02:15:37 pm »

Clear pic of the piston on preivious page.. The vavle pocket is much deeper than the amount you would be taking off.

BPellerine · « **Reply #44 on:** August 24, 2013, 03:34:43 pm »

just for a laugh I took an f3 piston and one of my rcs and put them side by side with a pin holding them at the height they would be installed on the rod the ring lands all line up perfectly but the outer edge of the rc piston is lower by at least I mm so this is a bit perplexing to me as the f3 piston is taller,any thoughts?bill

754 · « **Reply #45 on:** August 24, 2013, 03:37:32 pm »

F3 has bigger chambers..more room... Bill can you take apic of your piston f the dome, then valve pocket, so Jay can see it.. Thanks.

Terry in Australia · « **Reply #46 on:** August 24, 2013, 03:44:50 pm »

While you're at it Bill, can you take a nice clear pic of the underside of the piston? From memory the valve pockets are cast into the pistons so that the material in the domes are of uniform thickness, but it's been a long time since I saw my pistons. Cheers, Terry.

754 · « **Reply #47 on:** August 24, 2013, 03:50:38 pm »

The puston in pist #1 looks like it could handle 400 thou lift..

BPellerine · « **Reply #48 on:** August 24, 2013, 04:11:32 pm »

yes guys I will do that but being a computer idiot among other things I will have to get my son to do it will look and try to describe what I see the domes on the f3 pistons look taller too.bill

BPellerine · « **Reply #49 on:** August 24, 2013, 06:55:55 pm »

so here goes nuthin I did some measuring and here is what I have found
if these pistons f3 and rc rose together the outer edge of the f3 piston would be 2mm higher at tdc which I understand to be top of cyl.also the dome on the rc starts 2mm in towards the center.the dome itself is 61 mm across .the 2mm flat around top of piston is broken by the valve pockets on both inlet and exhaust.so at least the outer diameter of the piston is LOWER in the cyl than the f3.so at least in the k7 k8 I do not understand the clearance issue as the cyls are same height and the rc lower than stock at deck.the pistons do not show any sign of extra casting for valve relief.I would think that if there was a big issue terrys engine with lower deck height ie ko to 74? would have failed after 11000 rpm runs with big cam.just my thinking bill

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Author Topic: Need help with ID of RC piston application (Read 7638 times)