O Ring Head Modification : Please advise

[KANDY]

Hi All,
Thinking of doing O-ring gasket on RD400. Viton O-rings are available in the machine shop. I have few Questions, please advise.
Since the regular gasket is gone , the compression will increase automatically, so is it a considerable amount increase. Do I have to increase the volume in the Head, How much CC is ideal for the head. Or can I leave it as it is. Could you guys please put some light on this subject.

[Dvsrd]

At the very least, you need to check the squish band clearance with no head gasket installed. You can do this before machining the o ring groove. IIRC, the 400 gasket is 0.40 mm thick. Removing the gasket will reduce combustion chamber volume by 1.29 cc.
This will increase "trapped CR"  significantly,  and may require some machining of the combustion chamber bowl.
Any porting or other mods also come into play with regards to the optimal head volume.
I think Chuck will be the right person to answer this, after you have provided more detail info about your bike model and setup.

[rodneya]

You will have to install alignment dowels as well.

[m in sc]

if nothing else, def get the squish band corrected and the profile optimized. its not all about area or volume, but shape is as, if not more, important.  also a good idea to get the cyls skimmed smooth. .02

[JoeByrd]

I deleted the head gaskets on my and actually a number of other triples. I ended up using copper gasket sealing spray, first as a stop gap method to test the bike and ended up never doing anything more or having a leak, including Kawasaki H2-750s, which are notorious leakers.

I modified the combustion chambers to get the correct squish and head volume, I used a compression gauge to find the right amount and then CC'd the heads to match them up.

A hugely successful mod. Yes, just copper gasket spray.

[rodneya]

I deleted the head gaskets on my and actually a number of other triples. I ended up using copper gasket sealing spray, first as a stop gap method to test the bike and ended up never doing anything more or having a leak, including Kawasaki H2-750s, which are notorious leakers.

I modified the combustion chambers to get the correct squish and head volume, I used a compression gauge to find the right amount and then CC'd the heads to match them up.

A hugely successful mod. Yes, just copper gasket spray.

Did the same thing on my RZ50 back in the 80's, but we used to use something that was red. Cant remember what it was though. Never leaked even on a water cooled bike.

[KANDY]

Thanks for all the feed back. Will update once done.

[teazer]

Back in the day, O rings were not as readily available, so on our simple Villiers motor, the hot trick was to lap the head and barrel together, clean the faces and use high temp gasket goo  - no gasket.

Ah... The good old days.

[Gil Gallad]

on my gt250's i always use copper head gaskets, as i find the original ali ones are not that good and repro ones are useless. so i make my own. 0.3mm copper sheet, make them, anneal them and fit them. torque the heads down cold and again when engine is hot and done. never leak and you can use them over and over again if you anneal them again  ;D
cheers, gil.

[Dvsrd]

Back in the day, O rings were not as readily available, so on our simple Villiers motor, the hot trick was to lap the head and barrel together, clean the faces and use high temp gasket goo  - no gasket.

Ah... The good old days.

On 1990-2000, and most likely even current 600-1100 cc air cooled 2V Ducati engines, no head gasket is used. Just O-rings for the oil supply and return bores. And I have never even heard of any cylinder/ head leak on those engines.

[soonerbillz]

Excepting the obvious compression increase... what is the benefits of this modification?

[m in sc]

tightens the squishband which centralizes the burn better (to completely over simplify it). Also, they will just seal better.

[bitzz]

Back in the day, O rings were not as readily available, so on our simple Villiers motor, the hot trick was to lap the head and barrel together, clean the faces and use high temp gasket goo  - no gasket.

Ah... The good old days.

On 1990-2000, and most likely even current 600-1100 cc air cooled 2V Ducati engines, no head gasket is used. Just O-rings for the oil supply and return bores. And I have never even heard of any cylinder/ head leak on those engines.

ducati's have a spigot to seal the head, they've been doing that forever... and yeah, they leak like anything else when you raise the compression ratio. That joint was designed to hold stock compression ratios.
Gaskets, orings, seals and the like are used because they are cheaper than machining the surfaces so they will seal.
If you want to spend the time and effort, which equates to higher manufacturing costs, lapping the mating surfaces till PERFECTLY flat, the joint will seal without gaskets, seals or orings.
What I do:
a street bike gets RD400 1A1 copper gaskets, lapped cylinders/heads
a racer gets more compression, lapped cylinders/heads and O rings. (While you have the head on the lathe, or mill, to machine a new combustion chamber, you may as well Oring and pin the head (I made a jig, simple task) OH... and I O ring the head, not the cylinder. you replace cylinder a LOT more often than heads).