Weird leak RD400D

Fredg411 · September 23, 2020, 04:15:26 PM

Noticed some oil on top fin of cylinder. Figured gasket was leaking for whatever reason. Pulled head and found this on cylinder side of gasket. What caused this? A small Sharpie X exactly where the mark was. Scraped marker off cylinder with fingernail, so I can't show that. Last time head was off was 10 years ago (3k or so miles) for rings and seals. Don't remember marking the cylinder or why - maybe to keep piston with proper bore... No idea. Also don't know why I didn't clean it off them. I probably ignored it, thinking it didn't matter. Well, it did! It didn't leave a deep impression on the gasket - a thousandth or 2, but oil has been seeping very slowly - just a thin stain. Gaskets ordered.

Quick, stupid question. Engine has to be out to pull the jugs, right? Never tried.

m in sc · September 23, 2020, 04:24:50 PM

that is an odd shaped inclusion in the gasket. Ive used copper head gasket spray on the copper head gaskets for years, always seals up nice and tight.

Diablo007 · September 23, 2020, 04:56:48 PM

@m in sc
Thanks for the tip regarding copper head gasket spray. I'll try that on the next engine that is in line for seals and gaskets.

@Fredg411
I was able to remove a cylinder from one of my RD350's with the engine in the frame. Seems like it would be worth trying. Taking the engine out is a headache, but that might be because I haven't done it enough.

1976RD400C · September 23, 2020, 05:04:47 PM

The frame is designed to take the jugs off without removing engine. Your gasket looks to be beat up bad with scrapes and file marks on the edges.

Fredg411 · September 23, 2020, 05:18:53 PM

Not sure where the scrapes and scratches came from, been installed since 2009, I think they are original

- Vesrah. The X shaped mark is the impression left from a sharpie "x" I left on the cylinder. It sounds like these are not candidates for annealling, but copper spray gasket sealer might work?

Pleasantly surprised that jugs can be removed in frame...

Thanks,
Fred

m in sc · September 23, 2020, 05:21:43 PM

i wonder what kind of weird chemical reaction that had. very odd. id def get anew set.

Fredg411 · September 23, 2020, 05:56:18 PM

I don't think it was chemical, at all. The ink was hard and a thousandth or so thick. It was squeezed between the cylinder and gasket, just like any other foreign object. We tend to think that ink has almost zero thickness- apparently not so... Bizarre.

Those gaskets look to be brass plated copper.

I've just noticed that the X has faintly printed through to the other side - even weirder. Check it out.

rodneya · September 23, 2020, 07:14:42 PM

If you could scrape the ink off it was not a regular sharpie. It may have been the type filled with liquid paint with the push the tip in to draw thing.

m in sc · September 23, 2020, 08:08:21 PM

yeah. ^ exactly

Fredg411 · September 23, 2020, 08:19:05 PM

Well then, I'm completely out of ideas...

rodneya · September 23, 2020, 09:21:14 PM

Maybe they were right to tell us not to sniff those permanent markers when I was a kid.

Diablo007 · September 23, 2020, 10:57:31 PM

If I had to wager a guess it would be; the 'x' was made with a paint marker, the cylinder side of the gasket did not seal properly from the start due to the difference in height caused by the paint, somehow the outside edge did seal, and it took a while for the pressure to break the seal on the outside edge and cause a leak. Or...the mark was made with a permanent marker which prevented the gasket from sealing where the 'x' was, carbon built up where the gasket wasn't sealed, with the same end result. I've never marked a sealing surface with a marker that I can remember so I may be off with that hypothesis.

quocle603 · September 24, 2020, 10:27:21 AM

Mark beat me to it.

Yeah I had the toughest time sealing up my RD350 head. I annealed several copper head gaskets and it still did not seal up, even torqued it down pretty good.

Then I got some copper spray and thought it was a last effort attempt and did not think it would work but holy hell did it seal it up. NO MORE HEAD LEAK! :)

Quote from: Fredg411 on September 23, 2020, 04:15:26 PM
Quick, stupid question. Engine has to be out to pull the jugs, right? Never tried.

For RD350, you dont. Wish I knew more about RD400 but I dont think it does.

Organicjedi · September 24, 2020, 11:11:04 AM

Quote from: quocle603 on September 24, 2020, 10:27:21 AM
Mark beat me to it.

Yeah I had the toughest time sealing up my RD350 head. I annealed several copper head gaskets and it still did not seal up, even torqued it down pretty good.

Then I got some copper spray and thought it was a last effort attempt and did not think it would work but holy hell did it seal it up. NO MORE HEAD LEAK! :)

Quote from: Fredg411 on September 23, 2020, 04:15:26 PM
Quick, stupid question. Engine has to be out to pull the jugs, right? Never tried.

For RD350, you dont. Wish I knew more about RD400 but I dont think it does.

I've had my 400 cylinders off with the engine mounted. I think that's just a necessity with a 2 stroke.

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Weird leak RD400D