new things keep coming up so i’ll keep posting in this thread to not open new ones.
It’s the first time I service my engine (bough a used shifter) and when I took out the water pump I realized it didnt have gaskets but sealant instead, so it wasnt probably maintained properly, well then I took the engine head off and it also didnt have a head gasket, but some kind of O-rings or perhaps high-temp RTV silicon “gasket”.
What’s very strange is that the top of the block have these 2 “grooves” like O-ring slots that I’ve never seen in any manual or video, all I’ve seen are completely flat surfaces.
Are there some blocks like this? should I use a regular 99 head gasket? is this machined aftermarket to use RTV to increasee compression or something weird like that?
Many of the mod motos were modified to use an oring head gasket. I think they are viton vs silicone. Unsure if you could use an OEM Honda gasket on it. If you did it would probably lose a little performance which might not be a bad thing if it’s heavily modded.
I’m still not sure if those are O-rings or if its simply gasket maker silicon because I removed some excess inside the water ports and if you look in the pic theres also material around the head bolts.
So no OEM block ever came with these grooves? they were machined to use a thinner gasket? so weird to not just simply mill the head or block for higher compression than to go these lenghts for it, were they playing around racing regulations or something?
I’m not that concerned about the performance with a headgasket, but about it not sealing properly having those grooves, perhaps just going with gasket maker is the way to go…
If it’s gasket maker someone did it wrong… Replacements you might consult an engine builder with experience in mod motos. Probably could help you or sell you some.
So I suspect its indeed gasket maker but I can’t tell, they feel solid and not very mushy like an O-ring would as you can see in the picture a few posts above.
Well anyway I measured the grooves in the block and the inner one is:
That said, the oring is more for convenience in some ways. With how often the head gets removed over a weekend, using orings you don’t have to worry about keeping or finding head gaskets, nor worry about manufacturing variances.
As a class the mods are not very common, but folks who have experience with them are in abundance. Swedetech, DDR (Darcy Decoste Racing) off the top of my head would be able to help with parts I would say.
Given how common the CR125 and how its the same gasket for like 30 years it sounds like an strange mod for conveniance.
I’m looking for random O-rings and i’ve found ones tha match the size, any suggestions on material, there are many nitril ones that withstand 212F, would that be good?
I’ve sent emails to swedetech and DDR to see if they can help.
It depends on the application. It’s standard in competition karting and other high performance two stroke engines engines.
Running them hard in competition you could be changing the head gasket 4/5 times over a weekend at times.
Or run a single set of orings, keeping another set as a spare for the entire season knowing your squish clearance is going to be the same, (provided nothing else come loose)
But for just turning laps, not necessarily needed.
Not to mention the stock head gasket can struggle with an engine that’s now close to double its power in stock form. (Thinking back to when I ran mod motos)
