1969 CL350 cam lobe shape

[neildavies67]

Hi folks, recently acquired a (non running)1969 CL350 and finally got around to tearing down the top end. Pistons, head and valves heavily crusted in thick carbon deposits and strange pitting on piston crowns. Barrels seem in reasonable shape (although no "crosshatching" visible but was going to re-bore anyway) and compression seemed ok (by feel, not measured). Pistons were measured and are standard but the cam lobes seem like they have been reground asymmetricaly for faster valve closure (I think) - see pics. I assume this was intentional and not due to wear as all the cam lobes appear to be the same shape with some pitting at the apex. If this was a performance mod it seems odd due to standard pistons. Maybe heavy carbonisation due to failure to re-jet after cam mod? I'm just scratching around in the dark here! Anyone seen anything similar before?

[AshimotoK0]

That's a 'fat cam' from a K0/K1/early K2 model that was designated '286' which runs with the associated '286' rockers. The engine was detuned after the K2 and the cam became the '312' part with associated '312' style rockers (312 designation was for the SL350, the first 'K' engine to change over to the detuned cam) . The parts are not interchangeable  so need to be replaced in sets if swapping over. I can't do it for a couple of days but I can photo my 10K mile 'fat cam' from my '69 K1 CB350 to compare but  seem to remember the profile was similar to yours. Mine is really nice and not worn so will be a good reference. the 286  fat cam is much prized by classic racers and since it was prone to lobe pitting /journal wear  if oil changes not adhered too it is a bit of a 'hens teeth' item in decent nick.

Here is a supposed NOS one (286 type)

http://www.ebay.com/itm/HONDA-CB250-CB350-CL250-CL350-CAMSHAFT-NOS-/381992665371?hash=item58f089811b:g:R7wAAOSwtfhYrGS7&vxp=mtr

[neildavies67]

Many thanks for clearing that up AshimotoK0. The rockers were heavily worn and I now wonder if the previous owner has used the wrong type? Will check this evening! Do you know if these cams can be hardfaced and re-ground? Can anyone reccomend an engineering firm/cam specialist? Cheers!

[Bryanj]

An age old memory tells me that the cams were meonitic cast and the followers hardened. If you harden the cam and followers expect a life measured in minutes not years

[AshimotoK0]

Many thanks for clearing that up AshimotoK0. The rockers were heavily worn and I now wonder if the previous owner has used the wrong type? Will check this evening! Do you know if these cams can be hardfaced and re-ground? Can anyone reccomend an engineering firm/cam specialist? Cheers!

If later rockers are fitted ..real struggle but I have seen it done in the '70's by some idiot...  then  later rockers (cam followers) are cast with '312' on them. Decent sets of rockers and camshafts do pop up on eBay particularly in the US but occasionally at the likes of DK Motorcycles or GovnorsBridge MC's. IMHO that will be a cheaper and less fraught way than refurbishing parts, unless of course you are building a racer..... The 350K in it's various guises sold by bucket load in the States so decent parts are out there if you look.

Don't worry too much about using the later 312 parts ..it knocks a couple of BHP off the engine but it's still a fair power output for the 325cc designed pre  1968. There are very slight differences between the camboxes for 286 and 312 cams but it's just concerned with shaped apertures slotting the camshaft in and the can be easily modded even with a Dremel tool.  Definitely worth joining HondaTwins.net forum as well as this. I have the same 'handle' on there. Having said that you are just as likely to get as much help on here.

The service manual and parts book for your bike are on here in my Dropbox links on this site.

I also have the 69 K0/K1 Parts manual but I have not scanned it yet.

http://www.sohc.co.uk/index.php/topic,8884.0.html

CB350/250K PARTS MANUAL

https://www.dropbox.com/s/2ohbdtqh5nvgvvf/Combined%20Honda_CB350_Parts_Catalog.pdf?dl=0

CB/CL 250/350K SHOP MANUAL

https://www.dropbox.com/s/8i51vjqqdvllazj/CB350ShopManual.pdf?dl=0

[AshimotoK0]

I now think the later  'skinny' cam still had a 286 Part No. not 312 , but the rockers that go with it are indeed designated 312 (see parts book)

https://www.cmsnl.com/honda-cb250k4-england_model8207/arm-valverocker_14431312010/#.WZ_XDPiGPIU


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[neildavies67]

Thanks for all the info Bryanj/AshimotoK0. I noticed that the rockers on CMS had the number 312 on the casting for early models but wasn't sure if this was just due to a "stock" photo being used? Just had a chat with Newman Cams and they will have a look at my parts. He said they would normally put a stellite pad on the rocker and re-grind the lobes if they weren't too baddly worn/pitted! He di say they have some k4 blanks so am wondering if anything could be done with one of those? Looks like I'm caught between a rocker and a hardface (sorry!).

[K2-K6]

In your first post you mention "strange pitting" in the piston crown,  this could by associated with detonation in the combustion chamber, ie pinking as it's more commonly called.

In more extreme cases it's sometimes accompanied by scuffing of the piston skirt near to the gudgeon pin boss and can fracture the ring lands of top and second rings.

[neildavies67]

Cheers for the info K2-K6! I have posted pics of the pistons below! Going back to the cam and rockers issue, I have also posted pics of the wear on the cam followers and any identifying numbers on the rocker castings. The mystery deepens as there are three different numbers: 11, 26, 8 (or 6) & 11 (although they all seem identical in appearance to me?). The two rockers on the left were located on the left & right inlet cam lobes while the two on the right were located on the left and right exhaust cam lobes. Does anyone know if the numbering is significant? Should I be worried? For the pistons, the badly pitted one was located in the left cylinder. There does appear to be some scuffing on the edge of the piston crown. As i said previously, because the pistons are standard I will be re-boring. Not sure whether to just go up one size or bite the bullet and go big bore kit! Anyone have any experience either way? I will be getting Mikuni VM30s carbs as the Keihins were buggered! I've been quoted £330 jetted for standard.

[AshimotoK0]

Rockers are badly worn all four rockers are same part no. But you must use 312 rockers with later cam and do not use 312 rockers with early cam. Interesting to know how much Newman cams quote you .It used to be Joy engineering back in the day but heard good things about Newman

[Bryanj]

I would hazard a guess that the piston markings are ingress of hard crap, are there similar marks on the head? Used to see marks like that when piston rings shattered but that needed a destroyed ring groove as well. Ash is the man to listen to on these motors, but like I said I remember way back in the late 70's a racer friend had a cam hardened and reground and it didn't last a practice along with the hardened followers, Damage on the followers like that is probably bad oil flow as people do not clean out the centrifugal filter often enough

[neildavies67]

Evening folks, once again many thanks for the wisdom! This is my first project like this and I'm loving every minute, despite the never ending challenges! This site is an amazing resource and I am most grateful for all the help, the information has been really useful! The head is pretty coked up but no obvious damage although I will give it a clean tomorrow and inspect thoroughly. While the pistons are pretty crappy there is no catastrophic damage with rings and lands intact. Newman cams quoted £60+vat for camshaft re-grind and £37.50+vat for stellite pads on each rocker but this was sight unseen and he asked me to send them in for an initial inspection so price is obviously subject to change. I notice on CMSNL that the rockers for the USA K0 CL350 have no numbers visible on the casting but do have a right angled "hump" on the spine of the cam follower end, the same as my pics, whereas the 312 rockers have a smoother curve on the spine of the cam follower end. Do people think I'm safe making the leap that I have the correct rockers for the early camshaft?

[AshimotoK0]

I am 'darn sarf' at the moment but when I get back I will dig out all of my parts and photo for you. If you have the early cam and followers marked 312 like the CMS pic I posted then they are  wrong but if no 312 markings then they will be early 286 parts .Personally I  would search for a decent used set ...That's what I did with my CB72 and one of my CB250k0's ...K3 and K4 models used the later camshaft and rockers and will be more readily available than the earlier parts.

[florence]

 I read that you are considering different carbs.  I have considered the same with mine.  In a box of bits I have a pair of Amal concentrics with manifolds designed to bolt onto CB350K head.  Has anyone tried these and know if it works well or not?

[AshimotoK0]

Got home ...rule #1 stay off the M1 at Bank Holiday time 

Here are some pics . My late cam is not here so I couldn't photo it.

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