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Post by repherence2 on Jan 26, 2021 16:13:33 GMT -5
Maybe you could mix the oil with the gasoline? 🤔 That would work if it was a Rotary engine  |
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Post by 90GTVert on Jan 27, 2021 12:52:47 GMT -5
Finally got the exhaust valve events. It took me forever. These engines just have the small access hole for valve adjustments or this sort of thing and of course the exhaust is the one on the bottom. I kept trying to setup an indicator so it matched the valve angle well enough. I ended up making a steel plate that bolts to the exhaust studs. Then I put a small magnetic base holder on there. I kept moving and checking and moving and checking till I eventually got it situated to show the highest lift (should mean the best alignment). The actual checking didn't take that long, just setup.
Looks like 48° BBDC EVO and 7° ATDC EVC; both @ 0.050". That makes for 235° duration (48+7+180). Max valve lift as measured was 0.302".
I'm glad I did that check, because when I went to set the valve lash to 0 for the timing checks, there was already no measurable play. At least I couldn't fit the 0.0015" feeler in there. I'll set it to spec (0.004"-0.005") and also check the intake valve while I'm at it. I may check the intake lift specs just for giggles, but I may not. It depends if that one will take hours or if I can find a spot for an indicator up there more quickly.
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Post by aeroxbud on Jan 27, 2021 14:03:35 GMT -5
Just goes to show. Even on a new motor, it pays to check before you run it.
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Post by 90GTVert on Jan 27, 2021 18:18:37 GMT -5
I checked the intake side too. I couldn't fit a feeler gauge in there either. Luckily, the exhaust mount and the intake bolt spacing are the same so I could move the plate for the magnetic base up top. Specs were close. 0.305" lift and 237 duration; both just a hair over my exhaust side measurements. I think they're probably supposed to be the same and it's a measurement error. Most likely the intake side is closer to correct because it was easier to get a good angle up top.
I just wanted to get a rough idea for an exhaust calculator, because I figure I'll be off of any calculations anyway with the tapered pipe and from errors trying to make the exhaust. Now I'm trying to resist measuring more properly. What I'm measuring at the valves is not correct to cam specs unless the rocker arm ratio is 1:1. I have no idea what the rocker ratio is on these. If it's 1:1, they're fine. If they're say 1.5:1, it's all off because I'd have to measure 0.075" valve lift to equal 0.050" on the cam. I really don't think it matters much for this particular pipe if it's off by multiple degrees... but the nerd in me that likes to write things down...
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Post by 90GTVert on Jan 27, 2021 22:53:52 GMT -5
I didn't see anyone saying what the rocker ratio is for these. I have a feeling it's 1:1 or close, because I don't really think these small OHC engines use a lot of aggressive ratios. I could be wrong about that. I emailed T-Bolt USA to ask if they happened to know. They seem to be the go-to source of info for Chinese pit bike engines, so maybe they'll know and I won't even be tempted to mess with it anymore.
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Post by captincvmn on Jan 27, 2021 23:01:28 GMT -5
You know you want a custom grind cam with a loppy idle and roller rockers.
Next you’ll be using a throttle body of a Chevy 305 engine and adding some red Cherry bombs.
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Post by 90GTVert on Jan 27, 2021 23:30:57 GMT -5
Next you’ll be using a throttle body of a Chevy 305 engine and adding some red Cherry bombs. After I bought my first scooter, a friend picked up a new 4T. As soon as he got it we chopped off the muffler and put a red Cherry Bomb glasspack on it. It was obnoxious, even after welding in an endcap to reduce outlet size, and was replaced with an FMF muffler from a small dirt bike. |
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Post by repherence2 on Jan 28, 2021 13:10:32 GMT -5
Just goes to show. Even on a new motor, it pays to check before you run it. A coworker of mine used to buy cheap 4t scoots off CL. It was always scoots that the owners said that it didnt run well or had a hard time starting/running. He would buy the scoot, push it out of sight of the previous owner, reset the valve lash to specs and ride it home. |
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Post by 90GTVert on Jan 29, 2021 19:17:41 GMT -5
T-Bolt USA just got back to me. They don't know the rocker ratio on these engines or any info on the stock cam. So much for easy.
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Post by 90GTVert on Jan 31, 2021 7:56:55 GMT -5
I've been looking up aftermarket cam specs. Seems like most are 0.260-0.275" and I've seen 0.305" lift at the valve. I've either got a big cam stock or the rockers are not 1:1. I guess I'm gonna pull the cam out to measure the base diameter vs lobes and see what the lift is directly at the cam. Unfortunately the KLX style head has no large valve cover that allows access to the cam like some heads. You just have small covers over each valve and a side cover to access the sprocket and cam. Once I figure out rocker ratio, I can redo the checks for wherever 0.050" cam lift actually is. Sounds like it's probably going to be 1.1 - 1.2 rocker ratio. So most likely I'll be looking for 0.055-0.060" lift at the valve, which I think will make next to no difference vs what I've already recorded.
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Post by captincvmn on Jan 31, 2021 9:31:38 GMT -5
Lift and separate?
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Post by 190mech on Jan 31, 2021 16:38:30 GMT -5
I think they call it 'lobe centers' in the 4stroke world..  |
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Post by 90GTVert on Jan 31, 2021 23:52:21 GMT -5
I pulled the cam out today and measured it with a dial indicator and with a caliper. Both showed 0.273" of lift for the intake and 0.267" for the exhaust. Well, actually the caliper said 0.2665" for the exhaust. That is much more on par with what I've seen when anyone bothers to put a spec on cams for sale.
The rockers have to come out to get the cam out, so I may try to measure those and get ratio from that. I think that may be sort of tricky to get just right with a long pad for contact on the lobe and such. Not sure what's worse... that or hoping that I aligned my dial indicator with the valve travel well enough for a close reading.
Previous valve lift readings were 0.305" intake and 0.302" exhaust. That would suggest about 1.12:1 based on intake numbers and about 1.13:1 based on the exhaust numbers. I'll give the valve lift numbers another try to see how it turns out.
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Post by 90GTVert on Feb 1, 2021 14:58:55 GMT -5
My first attempt at measuring a rocker arm didn't go that well. I ended up with 1.022:1, which only raised the valve lift by about 0.006" vs lobe lift. Nowhere near my last observed specs.
The problem is, it's really hard to measure. Everything needs to be measured as it would be on a straight line, but the pivot is at an angle. It's also tough because some parts stick out more than others and it makes it hard to even get a repeatable measurement.
I decided to try it a different way. I printed out graph paper and carefully marked out the positions of everything across a straight line. It still won't be a perfect result, but it's pretty close to where I thought it would be based on observed valve lift. I got 1.11:1 when using graph paper, and that put the lift to 0.300" intake and 0.296" exhaust. Previously observed was 0.305"/0.302" and I was thinking 1.12-1.13:1 based on those figures.
I also hypothesized that a picture could be used to take these measurements. It would have to be taken exactly straight on to the rocker though, or again you'd end up with variances based on angle that would throw it all off.
I'm still going to redo the valve lift checks, but currently I'm guessing that the ratio is somewhere between 1.10-1.15:1. While that's not a precise spec, at least anyone else that ever wanted to do this could be close enough multiplying 0.050" or 1mm or a max cam lift spec by something in that range. Who am I kidding? No one else bothers with this stuff. lol If everyone were nuts like me, we'd actually have cam cards with small engine cams and everything that I'm trying to figure out here would be over in a glance.
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Post by 190mech on Feb 1, 2021 18:51:49 GMT -5
Put the cam on V blocks,check lobe lifts with dial indicator.Assemble cam in head,zero lash rockers,dial indicate rocker travel at valve tip,then calculate the rocker ratio..Am I missing something here??
Yeah I know this isnt a scientific method,but works for the average redneck racer in the shed!
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