Top end clarification

I’m thinking about doing x30 or Rok. I read online that the top end of the engine lasts around 10-15 hours but what does that mean and do you have to buy a new engine after the engine has passed the top end or only parts of the engine? and if they are only some parts, which parts?

Normally, it means that the cylinder is honed and the piston, ring and connecting pin are replaced.

John,
Two strokes need rebuilding periodically since they run at very high rpm. The top end is typically done midway through a season and a full rebuild (bottom) at end.

There is some wiggle room. Top level teams rebuild top end and (and bottom) way more frequently than club racers. They want “fresh”
engines that “pull” as hard as possible.

Most folks balance the expense of rebuilds to their ambitions.

Engine rebuilds are usually done by a shop rather than the individual. Talk to an engine builder to get the scoop on what your rebuild schedule should look like given budget and ambitions.

Oh ok so I wouldn’t have to pay for a new engine is what I’m hearing. Do you know around how much a engine rebuild would cost?

It’s been a while but like 500-750 ish top end and like 1k-1.3k ish bottom?

We’ve got actual smart engine folks who will chime in.

Rotax these days apparently goes forever on the top end but sounds like a bag of hammers fighting a bag of cats. Point is, different engine packages have different rebuild needs.

I personally love x30 and the way it feels, sounds, pulls, but it really does like top end every 8hrs.

Reports from the pro field is that KA 100 is very economical rebuild-wise.

X30 top is a cakewalk to do yourself. I do mine at 15 hrs and send it to the shop at 30.

I’m thinking about doing my own rebuild if I can since it’ll be cheaper and I want to get my hands dirty and get to know the parts as well. Kinda want to feel more in touch with the kart and actually feel like I know what I’m doing xD. I mean, I can follow the YouTube videos on how to do it i guess. I’m just trying to race at a local track and want to do Rok since x30 and KA100 aren’t exactly the biggest classes in my area. I’m starting out with LO206 cause they’re much more competition, but knowing me I’m gonna probably want to eventually head over to the faster ones.

If anyone knows a detailed explanation of the costs of running a rok or x30 per season that would be great

Depends on how many races you have and how long the track is.

Assume tires will last 2 races on a ROK/X30 ($220). Will need a gallon or two each race of fuel ($15 a gallon locally for C12). Quart of Oil ($15). Chain should be replaced every 4-5 races ($30). New sprocket around the same time ($15). Rebuild carb at every 3-4 races $30.

So each race I would budget $175-200 for consumables.

3 Likes

So I’m gonna make like a hypothetical cost analysis. So let’s say I buy a new Rok GP engine for around $2800 and a used chassis for about $4000-5000. In an eight race season, lets say I buy a set of tires every two races so around $900. Lets say for a season i purchase around 2 chains for a season so around $60 and around $30 on sprockets. I can rebuild the carb 2 times in the season, so probably another $60. Plus costs on oil (i dont know exact costs). I am still unsure about engine costs, so lets say $700 top end every season and $1.3k for bottom end.

So my first season I would pay (including the kart): $8550-9550
My second season I would pay (not including kart): $3050

These are excluding race entry costs. Can anyone tell me what I am missing and if this is decently accurate?

$4-5k is a pretty expensive used chassis - that’s what I’d probably expect to pay for a new one. You should be able to find a solid used chassis for between $2-3k if you want something between 1-3 years old. Plenty of people are still competitive on karts well older than this too, so don’t feel like you need to get something as new as possible.

Are you planning on running local stuff at the same track? If you’re going to different tracks at all you’ll probably end up spending a little more on sprockets since different tracks will require different gearing. Otherwise you can probably get away with only needing a few in a year.

What fuel does your track/series have you run? 5 gallons of the leaded VP 98 octane drums plus oil ends up being around $100 and we go through most of that in a Friday/Saturday/Sunday race event.

You also may want to just budget a blanket “broken/spare parts” category in there. Accidents happen and stuff breaks - you never know when you’ll need to swap out a bent tie rod, steering shaft, spindle, axle, etc. That stuff will add up too.

Another question - are you just starting out or were you running a different class previously?

So next year I’m going to be running lo206 since there’s more competition (20 drivers per race) and cuz I’m new to the sport. But after a few seasons I may want to try Rok senior so I just wanted to know the costs associated with it. I am planning on just running on the local track. I just checked at the track sell 5 gallons of sunoco 112 supreme leaded race fuel for $75. I was just wondering how much would I be expecting to spend each season on average. I was thinking for first season around $8000 including the kart and then $4000 a season in case of accidents.

Got it. Those seem to be pretty good ballpark cost estimates then.

No rebuild with lo206. Change the oil.

Yeah I know I dont need to rebuild lo206 really, I meant the costs above would be for Rok by the time I switch over

It’s worth doing a head/valve rebuild periodically as the valve seats distort.

@KartingIsLife how often would i do a head/valve rebuild on the lo206 engine? is every 2 seasons reasonable?

I guess it varies with how much you do in a season. You could do a leak down test to guide the decision to do it as well.

In the local track there are 8 races in a season for the lo206 class, would every 2-3 seasons be a reasonable amount of time to do a rebuild?

A guy came into a club race in NH once and had a rotax he used to use for road racing. Sounded like a washing machine full of bricks. he hadnt rebuilt it and had around 60-70 hours on it

Ooh I can help on this one! 206 requires practically no engine work other than changing the oil and checking the carb. You would have to get it done by a shop since 99% of series’ run 206 sealed. Ive done 3 seasons on a world formula and could probably double that without losing any performance.