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Author Topic: Possibly entering the 378 club!  (Read 5037 times)

Offline Sderbyshire

  • Posts: 254
  • Into Sailing, classic Triumph cars and motorbikes.
Possibly entering the 378 club!
« on: Jun 01, 2018, 04:34:19 »
Hi everyone, iím back after a period away from messing with my 360.

Have an oil weep from the head to barrels join, both sides, so am going to strip the top end down and potentially bore and install gs850 pistons.

Looking on ebay there are new aftermarket pistons available, or old engines.

Which should i go for as i think NOS are pretty rare these days?

Iím competent with a spanner but havent rebuilt an engine before, so want to keep this simple......

From reading threads on here and hondatwins i think i need to bore the barrels, and deck the pistons by adding a copper base gasket of the appropriate thickness?

Anything else essential?

Steve

Offline Sderbyshire

  • Posts: 254
  • Into Sailing, classic Triumph cars and motorbikes.
Re: Possibly entering the 378 club!
« Reply #1 on: Jun 03, 2018, 12:36:45 »
Took a break from decorating to tear down the 360 motor!

All went very well, no problems at all.

Previously iíve only uad the rocker box off but judging by the red Ďgasket sealerí on the base gasket someone has been here before?

So now i need to source a pair of gs850 piston sets and then have the barrels opened up to suit.

I want to keep this simple so am not changeing anything unless i need to, any suggestions as to what extra work is essential/worthwhile while i have the top end in bits?

Steve

Offline crazypj

  • Posts: 13216
  • Split personality, I fake being smart
Re: Possibly entering the 378 club!
« Reply #2 on: Jun 03, 2018, 13:42:10 »
You'll need a new head gasket for the larger bore, I recommend solid copper for head and base, better heat transfer. You'll need to get bore done first so you can check clearances to order correct thicknesses to get around 0.040" piston to head clearance
You WILL need heavy duty clutch springs with bigger motor, they are barely adequate for stock engineIt's a REALLY good idea to do various oil system modifications, need clutch and generator cover gaskets as covers have to come off.
 If you havcent looked through Miniature Ninja's build you should, he's got pictures of various mods and it will beeasier than looking through my 360 build/blog to find the informationWhen it's all done you can treat it as a very reliable high rpm Triumph 500, will be about same size, weight and power output but with an extra couple of gears and a higher cruising speed (80mph is generally no problem)As for after-market or used, doesn't really matter as bore should be matched to piston size, use 0.0015"~0.0017" piston to cylinder clearance
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline MiniatureNinja

  • Posts: 490
Re: Possibly entering the 378 club!
« Reply #3 on: Jun 03, 2018, 13:53:48 »
I've recently "completed" my 378 build, although I have yet to fire it up pending finishing the wiring. Last week of School for the kiddos has been holding things up for me.

notes and comments:
I ordered custom copper head and base gaskets from coppergaskets.us as PJ said you need to have the new pistons in the bored out cylinders to measure how far up they stick out so you can get gaskets made in the correct thickness. so steps: 1- buy pistons 2- have cylinders bored out to match pistons with proper piston/cylinder clearances 3- install and measure deck height 4- order gaskets 5- put it all back together again (dont worry, you will do this about 10 times before it's all done)

my build has some other complications as I have also gone the route of larger valves and some other things - but suffice to say that while you've got the engine apart it's more than worth it to take care of some of the oil passages that plague these engines, that will add some time and effort to the build but absolutely worth it and most likely necessary too.

any reason you took down the motor?
there are things that should be done to it - like tensioner replacement, filter cleaning.
my engine was as clean as a whistle inside and by doing a "simple tear down" I ended up doing everything in the book to this motor! LOL it's an addiction
« Last Edit: Jun 03, 2018, 13:55:34 by MiniatureNinja »
'75 Honda CB360 - thread

Offline Sderbyshire

  • Posts: 254
  • Into Sailing, classic Triumph cars and motorbikes.
Re: Possibly entering the 378 club!
« Reply #4 on: Jun 03, 2018, 14:49:43 »
Thanks both for the constructive replies.

Iíll look into the oil mods and make those, filter cleaned out not long ago.

Iíll also read minatureninjaís blog, as iím unsure exactly how to calcilate what base gasket thickness iíll need. Will then buy copper as recommended.

Thanks again!

Steve

Offline Sderbyshire

  • Posts: 254
  • Into Sailing, classic Triumph cars and motorbikes.
Re: Possibly entering the 378 club!
« Reply #5 on: Jun 08, 2018, 10:24:33 »
Hi all

Awaiting delivery of a pair of aftermarket gs850 pistons from Japan...... so tore the head apart and opend out the exhaust ports to more closely match the ex gaskets.

Couple of pics attached.

When the pistons arrive iíll have the barrels bored out to suit, i went for 70mm pistons.

Meantime iíll read up on the oil mods and get those done ready for reassembly, 10 times !

Steve

Offline crazypj

  • Posts: 13216
  • Split personality, I fake being smart
Re: Possibly entering the 378 club!
« Reply #6 on: Jun 08, 2018, 11:11:53 »
Should be interesting. Doesn't 70mm give you a 391?
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline Sderbyshire

  • Posts: 254
  • Into Sailing, classic Triumph cars and motorbikes.
Re: Possibly entering the 378 club!
« Reply #7 on: Jun 09, 2018, 04:40:21 »
Iíve had a search but struggling to find the 360 oil system mod info.

Could someone point me in the right direction please?

Thanks

Steve

Offline Sderbyshire

  • Posts: 254
  • Into Sailing, classic Triumph cars and motorbikes.
Re: Possibly entering the 378 club!
« Reply #8 on: Jun 09, 2018, 06:22:29 »
Is this the oil mod that i need to do to improve oil flow to the head?

Seems to be a very small opening out of the edges of the transfer piece, just removing the Ďstepí ??

Steve

Offline MiniatureNinja

  • Posts: 490
Re: Possibly entering the 378 club!
« Reply #9 on: Jun 09, 2018, 16:01:36 »
Is this the oil mod that i need to do to improve oil flow to the head?

Seems to be a very small opening out of the edges of the transfer piece, just removing the Ďstepí ??

Steve
Yup, that's the way I did mine (well duh, that's my photo) but also the way PJ had done his. Basically you're just removing some of the restriction this bypass part has, allowing more oil through the ports and less dumped out the bypass.
'75 Honda CB360 - thread