F20C rebuild

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wrightcomputing
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F20C rebuild

Post by wrightcomputing » Sun Sep 24, 2017 9:09 pm

Hi all,

I'm new here but this forum was recommended from the Locost forum. I built Scrap Metal a tube frame DMod Autocross car that had an F22C (Honda S2000) engine. The car can pull close to 2G when autocrossing. I destroked the engine to 2.0 by swapping the crank rods and pistons from an F20C. Since the swap I had oiling issues on 2 occasions the first the cams went dry and basically seized. I replaced them with the spare set from the junk F20C I bought. Then I got rod knock in cylinder 3 which turned out to be a spun bearing.

I am currently rebuilding the engine, I have no experience but am a keen learner and looking to do it right this time so the engine last a long time. The engine is completely apart and I am slowly going through cleaning everything to make sure all the crap from the spun rod is gone. I have had the crank repaired with a 0.25mm grind and ordered oversized race bearings for it. I have also ordered 12.5:1 compression pistons and lightweight connecting rods as I needed a new rod anyway and now is the time to increase the compression. I am also working on getting a drysump kit from the UK to hopefully prevent any future oil issues.

My goal is to fairly safely get as much power from the engine on a reasonable budget. For autocross I probably only put 200 miles per year but very hard miles. The class allows up to 2.0L Naturally aspirated. I will run the engine on E85 once it is rebuilt.

Anyone know where I push the RPM to. When it was a 2.2 it handled 9,000 rpm fine. Now with the 2.0 I plan to go a little higher maybe 9400 due to lower piston speeds. For autocross the extra speed in 2nd gear is crucial. I am currently around 73mph at 9,000 in 2nd (3.72 rear end). Getting closer to 80mph is ideal.

I am looking for any advise on an steps I should take when rebuilding or anything I should pay particular attention to. Thanks in advance for any assistance.

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Re: F20C rebuild

Post by englertracing » Sun Sep 24, 2017 9:35 pm

If you have good rods and valve springs what's wrong with more rpm?

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modok
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Re: F20C rebuild

Post by modok » Mon Sep 25, 2017 1:27 am

When the crank is smaller you get undersize bearings. undersize bearings for undersize cranks.
Oversize would mean the hole the bearing fits is bigger, and IMo they would be nice to have but not available.
Leading to.... Check the block. Those things are tricky to line bore and do distort like crazy if the bearings get hot.

Have you figured out what caused the loss of lubrication? did you have an oil pressure light?
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Re: F20C rebuild

Post by joe 90 » Mon Sep 25, 2017 2:03 am

modok wrote:When the crank is smaller you get undersize bearings. undersize bearings for undersize cranks ?



I tell kids that all the time but they tell me I'm wrong.

LOL.


I've had some very rude comments back.

From kids




But anyway....if you've destroked it and you've fitted 12.5 to 1 pistons, it's unlikely to be 12.5 to 1 so it needs careful measurement to find out what it really is.

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Re: F20C rebuild

Post by wrightcomputing » Mon Sep 25, 2017 7:59 am

So bearing I ordered were the correct ones I guess they are undersized. Unfortunately I do not have an oil pressure light, the only gauge I have is AFR. In Autocross you never have time to look at the gauges. I plug in my laptop for diagnosis.
Unfortunately I do not know what caused the loss of lubrication. However by installing a drysump I replace the oil pump and pan. As long as the engine is clean that should fix the issue.
When I de-stroked it I used the stock rods and pistons from the F20C. This time I decided to get new pistons and rods and increasing the compression is one of the few ways for me to gain power. The new parts are on order and I will be balancing them once the arrive. 12.5:1 is from the manufacturers spec sheet, they would be 13.1:1 in the F22C with the longer stroke. I'm not sure the exact compression ratio matters as the tuning will be the same regardless.

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Re: F20C rebuild

Post by joe 90 » Tue Sep 26, 2017 6:09 am

wrightcomputing wrote: I'm not sure the exact compression ratio matters as the tuning will be the same regardless.
Are you sure?

Does that also mean it'll also break the same regardless?

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Re: F20C rebuild

Post by wrightcomputing » Tue Sep 26, 2017 6:53 pm

I'm not sure now. Care to enlighten me on specifics. I will be taking the car to my tuner to get the tune done as he has done a great job previously. What differences do I need to look out for?

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Re: F20C rebuild

Post by pdq67 » Wed Sep 27, 2017 7:20 am

Come on Joe, quit biting at the guy!

pdq67

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Re: F20C rebuild

Post by joe 90 » Wed Sep 27, 2017 3:40 pm

Well if you're CR is going to change , then so is the ideal timing curve.
Same if you change the fuel.

The first thing (to me) to determine is why it blew up.


Was it a bad tune?
Was it oil starvation.

Both can cause a big end failure.

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Re: F20C rebuild

Post by modok » Thu Sep 28, 2017 2:02 am

Your initial post it's not really clear what it is you want to talk about. It could be about what caused the problem, it could be about souping it up, or it could be you'd like some advice about how to build an engine, or just chat back and forth , but I can't tell.
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Re: F20C rebuild

Post by wrightcomputing » Thu Sep 28, 2017 1:02 pm

I'm basically looking for advice on rebuilding the engine. I tried to provide as much info as possible and guess I didn't really ask anything specific in the process. For the rebuild process I an replacing the bearing, rod and pistons. Other than that just giving it a good clean. Any other step that I should take. I am aware that there are lots of things I can do but I am stretching the budget as it is.

Also if anyone is experienced with the F20C, similar engines or adding compression to make power and has some good tips I would love to hear them.

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Re: F20C rebuild

Post by modok » Mon Oct 02, 2017 8:43 pm

Sorry you probably didn't find what you were looking for.
As you are following the directions in the service manual ect, and the instructions for whatever aftermarket parts you will be using, have any questions about the speifics please don't hesitate to ask.
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Re: F20C rebuild

Post by wrightcomputing » Mon Oct 02, 2017 10:00 pm

No problem thanks for responding. The pistons arrived and I installed the crank, rotated the engine to find that cylinder 3 was scored. Not sure how I missed that. Anyway I had a good long chat to the guys at InlinePro who are very experienced with the S2000. I am going to ship them the block and they will machine it and custom make pistons for me. One good thing is they can do any compression piston so I am going to go as high as possible probably 14.5:1.
They also explained that the failure was most likely down the to baffle I installed in the oil pan. I had a feeling that may have been an issue but could not find anything to support it. He also gave me a couple of other tips when using the F20C as a race engine including a timing chain tensioner upgrade that they can do, replacing the coils which tend to go bad over time and a few other things.

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Re: F20C rebuild

Post by joe 90 » Tue Oct 03, 2017 1:55 am

So if piston no 3 is scored and BE no 3 spun.

You think it's oil starvation?

It depends which happened first.

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Re: F20C rebuild

Post by Cubic_Cleveland » Tue Oct 03, 2017 7:54 am

joe 90 wrote:
Tue Oct 03, 2017 1:55 am
So if piston no 3 is scored and BE no 3 spun.

You think it's oil starvation?

It depends which happened first.
Generally the bearing will start to eat itself up, bearing material gets ejected it all directions through increasing clearance, and some of it ends up on the piston wall...

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