Possibly entering the 378 club!

Sderbyshire

Into Sailing, classic Triumph cars and motorbikes.
Hi everyone, i’m 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?

I’m 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
 
Took a break from decorating to tear down the 360 motor!

All went very well, no problems at all.

Previously i’ve only uad the rocker box off but judging by the red ‘gasket sealer’ 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
 

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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
 
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
 
Thanks both for the constructive replies.

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

I’ll also read minatureninja’s blog, as i’m unsure exactly how to calcilate what base gasket thickness i’ll need. Will then buy copper as recommended.

Thanks again!

Steve
 
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 i’ll have the barrels bored out to suit, i went for 70mm pistons.

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

Steve
 

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I’ve had a search but struggling to find the 360 oil system mod info.

Could someone point me in the right direction please?

Thanks

Steve
 
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 ‘step’ ??

Steve
 

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Sderbyshire said:
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 ‘step’ ??

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.
 
You'll want to open these ports 1/32' more...

oilhole.jpg


Then the clutch basket...

clutchmod1-1.jpg


And try to find a CJ pickup. Although, you can get away without a CJ pickup with good oil level maintenance and limited side stand idling.

All those pics are photobucket, which means they may not be showing up unless you have the fixer extension.
 
Thanks both!

I’ll dremel the bypass as per your photo Minatureninja.

Irk, what size holes are you suggesting i drill in the clutch basket?
And what sise is ‘opening out by 1/32’ , do i drill that or file it bigger??

Thanks again

Steve
 
They're the oil passages bringing oil to the top end. I can't remember exactly what size the holes are now, but you're just making them slightly bigger- 1mm or 1/32" bigger.
 
Sderbyshire said:
Thanks both!

I’ll dremel the bypass as per your photo Minatureninja.

Irk, what size holes are you suggesting i drill in the clutch basket?
And what sise is ‘opening out by 1/32’ , do i drill that or file it bigger??

Thanks again

Steve
I drilled the headbolt oil holes out to 3/32 and used either a 9/64 or 5/32 bit for the clutch basket (basically just what fit between the splines)

Sent from my SM-G955U using DO THE TON mobile app
 

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Thanks MinatureNinja

Whats the point of the clutch basket drillings?

The pther two mods allow more oil flow to the head, but i dont see what the clutch basket holes do?

Steve
 
That and the HD clutch springs help clutch performance, especially with the bore.
 
as Irk said, it improves performance

it does this because it allows the oil in the clutch to flow out of the plates at RPM when the clutch is disengaged and run much cooler. cooler oil = better performance overall
 
It makes clutch run cooler. Oil flows through the plates all the time engine is running, (it's a 'wet' clutch) this mod directs more. oil through the center plates so they are less likely to overheat. When you pull clutch in plates disengage and oil flushes any 'dust' It's used on 200+bhp bikes so it must do some good ;D (although I've been doing mod since 1970's, kinda sucked trying to explain it to 'experienced' mechanics)
 
Excellent, thanks guys.

I understand about the clutch being cooled by the oil, although i’m more of a Ducati dry clutch man really!

HD springs ordered and i’ll get my drills out :)

Steve
 
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