bottom split case sealant & reassembly

[vinty200]

Well, I'm in deep now! CB200. A low compression finding last fall evolved into a top end rebuild. Upon first attempt at reassembly, a piston ring snapped and fell into case. I cracked it open to fish out chunks. Painful lesson, but I'm glad it happened because it was a mess down there and needed just as much work as the top end. Anyway, I will be ready to reassemble (again) in a few days.

I've seen a lot of comments posted here about the proper way to seal the lower cases.

The FSM says "Apply a uniform coating of proper sealing agent to the crankcase mating surfaces". (plural surfaces). Meaning sealant should be applied both sides of the case? I'll be using Hondabond 4 and I know I need to keep it thin.

Reading other posts on this topic, I got the consensus (maybe incorrect) that sealant was normally only applied to ONE side of the case? which is correct?

I also interpret from various postings there is no consensus on when to apply sealant to any other gaskets (some assemble dry, some use copper spray, some use hondabond, etc).
I don't think the gasket set I have were NOS - does that mean I should consider using hondabond on those as well?

Thanks all!

case reassembly.jpg

[ancientdad]

Personally, I put Hondabond on the upper case but you could also put it on the lower case surfaces if you chose to do it that way, but only on one of them, not both. The upper and lower cases were manufactured to very good tolerances so only a thin layer is necessary to seal. I typically don't use any sealer of any type on the outer cover gaskets, although I do use a thin smear of either Hondabond or silicone sealer around the alternator wires grommet where it fits into the left crankcase cover as the rubber, which is supposed to seal engine oil in, gets hard with age and can leak a bit. The discussion about using some type of sealer on the top end gaskets is based on certain engines and owners' personal experiences with seepage from some gaskets, like the 450 head gasket can seep oil around the cam chain tunnel areas and sometimes around the flat o-rings on the dowel pins over the 2 right side studs where the oil flow goes up to the top end parts. I'm not all that familiar with any seepage history for the 175/200 engines in the top end gaskets as it's been far too long since I rebuilt one of them, but others here might have experiences to relate about that aspect. Most gasket sets from our usual suppliers are typically good enough quality that they are comparable to factory gaskets for oil sealing purposes.

[old timer]

I bow to Toms expert advice . I use a childes stiff art bush from K_Mart. and put a very thin amount on both surfaces of the lower cases. I add a little dab where the cases meet the bearings. Before adding the sealer I use a 15 inch flat fine ******* file on all mating surfaces to level any high spots . Lay it flat on the surface and draw it at different angles. High and low spots will show up. Then clean ,clean , clean. I use no sealer on any surface except the lower cases. Any way it works for me. Some builders will use a thin coat of 10-40 oil on the new gaskets. I have done both and didnt have any leaks ether way .I heard one member took so much of his head trying to get rid of a high spot that the valves hit the pistons when he got it together. He was using a rough cut file. You just want o clean it up.

Bill H

















Bill H

[Richard Pitman]

On my 175 engines (same as 200 for practical purposes ) I assemble the crank and gears etc into the inverted top case, then brush apply a very thin coat of Hondabond to the mating surface of that case. The cases are such a good fit that hardly any sealant is required, unless of course a ham fisted PO has damaged the surfaces in any way. Assemble while the Hondabond is still tacky.

I have used grease to hold the outer case gaskets in place whilst assembling the engine, just a smear on one side only, didn't cause any leakage. No sealant anywhere else, except as Tom says, around the stator wire exit. Head gaskets assembled dry, no leakage to date, 8000+ miles on first engine now.

That said, I remember my original brand new 175 having an oil mist around the head joint at 22K miles, probably my fault for reusing the head gasket when piston rings were replaced during the warranty period. Outrageous really, my new bike having oil smoke from the exhaust after running in 'too gently' according to dealer. Dealership 'too busy' to fix my bike under warranty, Bladders of Sidbury, so one of the mechanics ( Fred the Ted ) gave me a set of new rings and left me and a friend to it. Quite why I meekly accepted this I can't think, these days I'd have been kicking their doors in.

[vinty200]

On my 175 engines (same as 200 for practical purposes ) I assemble the crank and gears etc into the inverted top case, then brush apply a very thin coat of Hondabond to the mating surface of that case. The cases are such a good fit that hardly any sealant is required, unless of course a ham fisted PO has damaged the surfaces in any way. Assemble while the Hondabond is still tacky.

I have used grease to hold the outer case gaskets in place whilst assembling the engine, just a smear on one side only, didn't cause any leakage. No sealant anywhere else, except as Tom says, around the stator wire exit. Head gaskets assembled dry, no leakage to date, 8000+ miles on first engine now.

That said, I remember my original brand new 175 having an oil mist around the head joint at 22K miles, probably my fault for reusing the head gasket when piston rings were replaced during the warranty period. Outrageous really, my new bike having oil smoke from the exhaust after running in 'too gently' according to dealer. Dealership 'too busy' to fix my bike under warranty, Bladders of Sidbury, so one of the mechanics ( Fred the Ted ) gave me a set of new rings and left me and a friend to it. Quite why I meekly accepted this I can't think, these days I'd have been kicking their doors in.

Thank you Richard!... but now i think i need a good definition for "Bladders of Sidbury". the interweb is not helping me there ;)

[Richard Pitman]

Thank you Richard!... but now i think i need a good definition for "Bladders of Sidbury". the interweb is not helping me there ;)

Try this:

W J Bladder date tbc (J0901021E28) | The Changing Face of Worcester (cfow.org.uk)

[fxray]

. . . Dealership 'too busy' to fix my bike under warranty, Bladders of Sidbury, so one of the mechanics ( Fred the Ted ) gave me a set of new rings and left me and a friend to it. Quite why I meekly accepted this I can't think, these days I'd have been kicking their doors in.

"Fred the Ted" . . . https://en.wikipedia.org/wiki/Teddy_Boy