Discussion and questions related to the course Practical Engine Building
I disassembled my seadoo jetski engine since it was running dry after a cracked oil cooler. It's a three cylinder 1630cc supercharged 300 PS oem engine. Used in stock class racing while running 800 rpm more than oem. It has 100 hours on it what i would compare to 100 000km on a car
I'm impressed how good the condition is. I have only found a cracked thermostat and very light wear marks on pistons and bearings
Pistons are in code shape, bore has no taper or out of round. Piston to wall clearance is in the upper tolerance of new engine and there is enough distances to the service limit. I do not see a need to go oversize.
However, thee honing Patern is not visible at all anymore. Should I get it honed and get new rings? Will honing effect piston to wall clearance?
hello most likey the bore will not be able to be honed at all because of the material used i would highly recommend contacting your local jet ski service agent to ask for your model
Nikasil must be diamond honed in order for proper cleanup. A diamond hone is the only hone that is hard enough to remove Nikasil from the bore to clean it up.
Thank you. I will talk to people who have lots of experience with these blocks. At least there are over size pistons sold by wsmparts.com
In general, if the honing pattern is not visible should the block be honed and old piston used with new rings if the piston to wall clearance is still acceptable?
If you're going to replace the rings then you'll need to hone the bores to give the rings a fresh hone pattern to bed in on. I'm not familiar with the particular engine and as Ross has mentioned, if it uses a nikasil coating or similar then this can become tricky. Nikasil is typically very thin which limits what you can do in terms of honing. The usual options are to replace the block or strip and re-plate the cylinders (which requires a specialist to do reliably).
I was at the machine shop. They used sanding paper on the phone and created a cross pattern deglazing the walls. I do not know whether this is enough for new rings.
Moreover, I just recognized that two cylinders are slightly out of round on two spots I have 0.05 and 0.04 while service limit is 0.02. However, it is the very top spot where the rings might not even reach.
My piston to bore clearance is on the upper tolerance and far away from service limit.
While nominal is 0.044 to 0.076 and service limit is 0.10mm
I see these options now:
1. Assemble with old rings
. 2. Assemble with new rings
3. 3. Sleeve the cylinders without Nakasil and assemble with new rings. There might not be anyone doing Nakasil coating in Thailand and I know that many people sleeve this block without Nakasil.
Please help me to take this decision so I can proceed ordering parts.
It's rather unlikely there will be folks familiar with the specific engine here, I'd suggest you check on-line with the various jet-ski and Seadoo forums and check with them - there may be known issues and/or easy work-arounds that will make your decision much easier to make.
Unfortunately, the only engines I recall with that type of bore coating were chainsaw ones, and so unlikely to be that relevant.