Honda Sky Head Gasket

Having removed the engine covers, on this Honda Sky, it is obvious that the cylinder head gasket needs replacing.....the last time I did this was in 1969, on a BSA Bantam, and, in the absence of a gasket, used gasket cement.....are there any disadvantages to doing this ? or is it blindingly obvious that the proper gasket should be used ? bearing in mind that gasket cements, or sealants, have moved on since those faraway days......

 

Tolerance levels are much tighter nowadays due to emissions etc. I would be inclined to use the proper gasket.

 

Thanks......yes, you are right of course, I shall send for one....as an aside, I wish that I had kept that Bantam, and the Lambretta that followed it....we live and learn I guess....

 

Yeah, the compression will just blow sealant away.
You could try and tighten the head bolts a fraction more though.

 

Thanks for that, going to borrow a torque wrench tomorrow, see what happens......if the head DOES have to come of, then I suppose it would make sense to remove the barrel as well, and replace both gaskets ?.....then I would also be able to have a look at the piston as well....

 

Yeah.
Easy job, exhaust off, 4 bolts and then it all comes apart.
The hardest bit is those plastic bits you already took off

 

The gaskets are due to arrive today....is there any need, these days, to use a sealant ? or, if the barrel and head are torqued down correctly, will it be ok without ?

 

You need them.
The head will burn through sealant and the base gasket needs to be there to set the squish so you don't get detonation

 

What I mean is, do the new gaskets require any sealant ? to help them bed in ?.....or just put them on "dry" and torque them down ?......

 

Just dry.
Use a dab of oil on the head bolts
And copper slip on the exhaust ones.

 

Thanks.....they have just arrived, hopefully get it re-built this afternoon.

 

Disaster !!…..just broken piston rings while putting the barrel back on.....totally my own fault, as I forgot that they only went on the one way.....I think this happened back in '69 as well, some people never learn.....about to order new ones, but I notice that there are two different sizes...39.5 mm and 40 mm....not sure which to order......a friend is breaking a Honda Bali 50 cc which I believe are the same, but is it really worth using second hand one's ?....just measured the bore, and it is a whisker under 40 mm, does that mean the rings want to be 40mm ?

 

Hmmm
Errrr 40mm I think...
Oh crap I'm bad at this, too many painkillers....
@Stevep

 

I guess that makes sense.....I suppose using old one's, even if they right size, is not a good idea ?

 

I've reused head and base gaskets plenty of times

 

All may not be lost......an old mate has just given me these....head, barrel, piston and rings off an old Honda Bali......they are identical to the one's on the Honda SKY......

 

Measure the piston, not the bore.
It's a 40mm piston as standard, there are several over size ones available but here's a link to a new standard size piston kit:

https://www.ebay.co.uk/itm/HONDA-SG...836000?hash=item44107456e0:g:eI8AAOxyoA1RQPc2

 

O.k....changed the piston, for the one out of the Bali.....everything seems o.k....except.....it now won't start, not torqued the head bolts down yet, and I also damaged the bottom gasket, the one the barrel sits on, could it be that I am not getting a vacuum ?

 

Did you change just the piston or piston and barrel?
Compression test would be in order..............with a proper tester, not your finger over the hole!

 

No....only the piston, I think maybe tomorrow I will change the barrel.....is it feasible to use a gasket "cement"....I see that a well known motoring chain advertise such stuff....otherwise it means sending for another gasket set from ebay, and waiting for it to arrive....