Refurbing a 39 year old engine! Any tips?

[SpannerMonkey]

Right, So I've decided on refurbing my PC50 engine a lil bit as she's a lil tired and wont take much to get it spot on.

What I'm DEFINITELY doing is:
Full bearing and oil seal replacement all over the engine
New casing bolts
Sending the clutch off to be relined (Centrifugal shoe type) as I CANNOT get hold of a replacement
Cleaning out the cases
Checking for general wear with calipers
Replace points as I have a brand new set already

What I MAY do if the jobs can be done cheaply or are viable...

Have the valves reground and seated
Replace the valve stem seals or whatever they are called
Replace the cam chain
Fit new piston rings and hone barrel

I just have a few questions as I have never done a non-bodged engine refurb lol

Can I fit new oversized rings (0.25mm) without an oversized piston?
Is it even worth having my valves reseated? I mean I want the job done properly on this engine, so should I get it done just to prevent further hassle?

Are there any other parts you'd replace while you're there just to be sure? I've noted the stuff which may be viable for replacement but I dont have that much experience with engine internals...

Do you guys have any other tips or suggestions?

Lastly... I have some high-temp high-pressure gasket stuff my mrs bought for me today... reckon this'll do my Base gasket, head gasket and rocker cover gasket? I have the NOS crankcase gasket and clutch cover gasket on its way
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[stinkwheel]

You might find quite a few C50 gaskets will fit it. I'd order a full C50 gasket set and see (worth a gamble at a tenner). That'll have head and base gaskets, valve stem oil seals and various o-rings. I really wouldn't use an old head gasket unless it is totally impossable to get hold of one and you shouldn't really need gasket compound either there or on the base gasket. Another option is to get a new one cut out of copper sheet.

If the valve seats are clean, leave them alone. If there are signs of leaking/pitting/scorching, lap them in yourself. Not difficult, just time consuming.

I'd also just check the bore. You sit a new ring square in the bore (push it in with the piston) and measure the end-gap with feeler guages. There will be a maximum size for this gap. If you're under it, hone and replace rings. If you're over it, rebore.

From your description, valve stem oil seals will be the one thing you must make sure to do. Don't replace engine bearings for the sake of it, some of them are a total pain to remove and then source new ones. If they've been sat in oil, they're probably ok. I reckon at most I'd do the mains and small ends, possibly the clutch.

If you can't get a base gasket, cut one out of the back of a cornflakes packet. This works well.

Go easy on the gasket sealant, you don't need to use it in most places. If you have a workshop manual, it should tell you where to use it and just use it very sparingly.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[SpannerMonkey]

my manual is from 77. I dont think gasket sealant had been invented haha!
Just had a look at the C50 gaskets, None of the top end gaskets are the same as the PC50 unfortunately...
I'll just have to go to a honda dealership, I'm sure the valve stem seals should be available somewhere.
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[27cows]

My one (obvious) tip is to be exceptionally careful when wielding the spanners. These little Honda motors break so easily if you overtighten something or go in a bit heavy handed.
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The RXS100: vehicle of choice for Chuck Norris

[SpannerMonkey]

[prawny1]

I have a spare set of pa50 clutch shoes, if they will fit you are welcome to them.

It's a three shoe dry clutch on mine that runs behind the front variator.
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[SpannerMonkey]

Thanks for the offer, but mine seems to be a 4 shoe arrangement...
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My bike? A YX140 powered one-off Monkey Bike, something a little different!