I recently rebuilt both the bottom and top end of my FL350. I performed both a vacuum and pressure leak-down test before installing the Engine. Not long after Engine break-in I noticed seepage around the base gasket about midway back on the side opposite the belt.


The Engine ran great - still idled fine. I decided to pull the Engine completely out to perform another leak test anticipating I was going to have to replace the gasket anyway. I sprayed a soapy water solution near the leak and sure enough it's blowing bubbles steady until it gets down to about 3psi (not positive whether it stops or just slows at ~3psi - I'll have to double check). I haven't tried a vacuum test yet.

I used the aluminum gasket I purchased from speedshop505 off ebay. I believe the builder scuffed both sides lightly with scotch brite pads and coated both sides with a thin layer of copper spray-a-gasket. I verified the 4 cylinder nuts are tightened to the correct torque spec.

As far as history: I had about 20 minutes on this machine after buying it before it ate a crank bearing and seized. Seller claimed the bottom end had been rebuilt about 5yrs ago but it hadn't been driven much after. When I disassembled it it had the fiber gasket that looked to be in good condition and showed no signs of leaking.

Everything I've read on here has said to NOT use the fiber base gasket. Do you guys scuff the aluminum gasket and use the copper spray? The Engine builder didn't like using the aluminum gasket (thought it was too thin) but I insisted that everyone on this board said to not use the fiber gasket so he did as I requested. I'd appreciate any advice on how to proceed.

Thanks in advance.

-powerchoke

I wonder if lapping would help. I have used the fiber gasket with Honda bond on my FL400 base gasket.

Hopefully CO will chime in soon.

I'm certainly no expert, but I also read that only the aluminum gasket can be trusted for reliability. I also used the copper spray when I assembled mine. didn't scuff it though and I don't see how that would negatively affect it.
I would agree with rmesser though, you should verify the gasket surfaces are flat by lapping them at least.

I have a pilot not an oddy so only tossing this out there, on the pilot I had good luck using the base gasket that comes with the rebuild kit, I did have a banshee that was ported so not alot of sealing surface on the outside at the transfer ports and had sucked a gasket, Cometic made an aluminum gasket that I then used and never had another issue, that gasket though had a thin rubberized coating and a silicone bead, probably yamabond type of material.
If it was me I would clean the surfaces well, scuffing won't hurt coat both sides of the aluminum gasket with yamabond, hondabond, or the like and torque it back together, make sure the cylinder and case are clean and flat of course.
the suggestion about lapping is good but I don't think you can do that without a major tare down, on the case the rod and studs are going to interfere, you also need to be carful not to get any of the FOD into the case and the cylinder is in the way for lapping the cylinder mating surface, that would need to be done on a lathe with the cylinder dialed in precisely.
on a side note, I know back in the day, some builders would put small punch marks on the sealing surfaces to keep the gaskets from moving, I would not recommend that unless someone who has been successful using this method taught you how.

I use the same aluminum base gasket on all my FL350 engines. I always use permatex ultra black on both sides of it. It is a better choice then the copper for the base gasket in my opinion. I only used the copper on the head gasket.

another plus for the aluminum gasket, I use copper coat, but was told to try either yamabond or permatex right stuff one minute black gasket maker

i agree on the lapping - i requested it but they only lapped the case halves and post-assembly it was too late. i'll verify surface flatness before assembly.

both the permatex suggestions say not recommended for use on parts that come in contact with gasoline.

anyone have experience with Permatex® MotoSeal® 1 Ultimate Gasket Maker Grey?

MotoSeal worked great. I had an extra aluminum gasket so carefully laid a small bead on both sides and put her back together. Held vacuum and pressure for 30+ minutes and no leaks since. So far so good.