Author Topic: Engine gasket sealant  (Read 13852 times)

Offline Eli_Slaminko

  • Advanced Member
  • ***
  • Posts: 5
  • Karma: +0/-0
    • View Profile
Engine gasket sealant
« on: December 09, 2007, 08:43:36 AM »
I'm in the process of rebuilding the top end of my '73 CB350 twin. Before I took it apart, there was a decent amount of oil seepage from the cylinder head to cylinder gasket. I've noticed that this is a common problem on old Japanese motorcycles. I'd like to prevent this when I put the motor back together. I've heard different theories about what is the best sealant to use. Some say no sealant, copper spray sealant is another idea I've heard. Any thoughts?

Offline Searchguru

  • Advanced Member
  • ***
  • Posts: 110
  • Karma: +0/-0
  • Suck, squeeze, bang, blow
    • View Profile
Re: Engine gasket sealant
« Reply #1 on: December 14, 2007, 01:30:11 AM »
Hi,
Hylomar Blue is what I would suggest. It is brilliant and doesn't stick anything permanently. Obviously you have to be careful not to block any oilways as this could have a catastrophic effect. At this time of year I would suggest either keeping the tube in a pocket or in a bowl of warm water to keep it at a workable temperature. It's not too thick but a cold tube of it and a cold cylinder head will just make it harder to spread out.
I think if you follow their instructions to the letter you should have an oil tight head gasket, or any other gasket surface you use it on. I think it was developed with Rolls Royce and is used by Formula 1 teams so it can't be all bad.
Tony.

Offline sono

  • Advanced Member
  • ***
  • Posts: 27
  • Karma: +0/-0
  • There's nothing like riding a Honda !
    • View Profile
Re: Engine gasket sealant
« Reply #2 on: December 20, 2007, 11:25:29 AM »
Be careful with gasket sealant on old honda bikes. I've got a CM400 1980. Soon after I bought it, I noticed that head and bottom cylinder gaskets were both getting wet and I got quite concerned.  >:(

I soon discovered that this was NORMAL if the bike had not been ridden for a while because the Honda gasket material is designed to absorb hot oil and swell to make a tight seal with very little specified pressure applied on engine mounting bolts.  ???

Sure enough, less than 500 km later, the oil stopped leaking as the most experienced mechanics had predicted. I'm not sure Honda gasket material is still designed like that but all Honda motorcycles and scooter engines I ever owned were from that period (mid-70 to mid 80's) and they all use simliar oil swelling material. :)

I later found in the service manual that using any sealant could actually CAUSE more leaks as well as poor cleaning or improper cleaning (using tools harder than aluminum).  :-[

Other brands of motorcycles more recent models and automotive industry may use other type of gaskets designed to used or designed to be replaced by gasket sealer. Lots of mechanics also use sealers because they don't have to wait for new gaskets when they perform repairs on an engine.  

I don't beleive in miracle cures that applies to any engine type. My old Honda motorcycles had accurate service procedures and head gasket installation did NOT include using any kind of sealer. If using a sealer, what would be the correct torque to apply ??? Don't assume that it would be the same.  ;)

Except for rare lemons like the early Honda Magna (see http://en.wikipedia.org/wiki/Honda_Magna) and a few known problems, I would think twice before going against Honda engineers advice.

Doing things the old way is often the best way to go with old bikes ! For instance, just try switching an old bike on synthetic oil (even JASO certified) : gaskets will often start to leak, wet clutch will start slipping, and it may start buring more oil simply because the engine is running too clean (too much detergent additives).
Using mineral oil (which is much better quality that it was in the early 80's) remains the best choice.

Old Honda engines were not as economical in gas and did not run as clean as they now do, but why on earth am-I still driving a 27years old motorcycle ? You must love them as they are intended to be. Also keep in mind that today's replacement gaskets are often better quality than OEM Honda which are often discontinued for ages anyway on a '73 !

I just had my CM400 cylinders and head refurbished to new. One of my valves oil seal failed, too much oil got into that cylinder so piston rings got gummed up and I lost compression on that side. Everything was still within standard specs, but I had to get new rings and have the valves cleaned and readjusted. In retrospect, It is no big surprise to see rubber oil seal fail after nearly 30 years,  but I have a lot of respect for engineers that designed such a reliable engine.

Good luck !

Martin

Offline swetty

  • Advanced Member
  • ***
  • Posts: 2
  • Karma: +0/-0
  • I love YaBB 1G - SP1!
    • View Profile
    • Email
Re: Engine gasket sealant
« Reply #3 on: April 19, 2008, 11:56:31 PM »
hi
gease is the best gasket you can get ..it stops triumphs leaking.
cheers swetty