Piston to valve clearance problem

914TWO · 06-14-2009, 12:25 PM

Hi everyone, I am a novice engine builder to be sure, and hope to find help with my current project. I am building a 2.2 engine for PCA GT-5 racing and have the following. My heads were done by a builder in Colorado who twin plugged them for me as I wanted to run JE 10.5:1 pistons. My deck height is roughly 1.45mm with a .25 base gasket. I have DC 80 cams at the recommendation of the of the guy doing my head work. My problem is that I cannot get the minimum piston to valve clearances recommended 1.5mm in., 2mm ex. It was suggested that I just use base gaskets to get the clearance I need, so I added 1.5mm more worth of spacers under the cylinders. I have the cams timed back to 5.8mm(Dougherty lists 6.2mm) and I am still slightly off of the clearance I should. Any suggestions on this problem would be greatly appreciated. Thanks.

Steve

camgrinder · 06-14-2009, 01:49 PM

How are you checking clearance? What was the clearance with the .25mm base gasket, and what is it now with the added shim?

914TWO · 06-14-2009, 10:43 PM

I am following Waynes book, and have been setting valve lash to zero after setting the valve timing, and rotating the crank and checking to places in the rotation where clearance problems will occur, and then running the valve adjusting screw in the minimum clearances for 1.5mm intake, and 2mm exhaust. The problem I am having now with all of the base shims is on the intake valve after TDC.

Walter_Middie · Walter_Middie's Garage

Quote:

I have the cams timed back to 5.8mm and I am still slightly off of the clearance I should have.

What was the clearance with the .25mm base gasket?

What would the cam timing be if you adjusted it to get the right clearance? I'm wondering if you're close, maybe the amount more of cam timing retard needed is insignificant.

cgarr · cgarr's Garage

How are you measuring the clearance?

914TWO · 06-15-2009, 05:51 AM

When I originally just had the .25mm base gasket I could not get any clearance on the exhaust valve at all. I took the pistons back out thinking I would have them milled down, even though JE said that they had never made pockets deeper than those, and the machinest locally said he could not do them for me, and suggested just shimming the barrells, and I contacted the guy who did my heads and he suggested the same thing. The shims have solved the exhaust side, but I now have the problem of the intake valve clearance. With the timing set at the recommended 6.2mm I have a problem at right about TDC on the exhaust, and as I back it down the clearance gets better, but I am just wondering if I have missed some basic concept, and am I giving up too much by just backing this off, or should I just use a different cam profile. I will be running a TEC3 fuel injection system if that would make any difference in this equation. Thanks to all for your thoughts.

Steve

camgrinder · 06-15-2009, 09:37 AM

The DC80 cams should clear with those pistons. I would use the clay method to check the V-P and find where the interference is.

911pcars · 06-15-2009, 09:39 AM

Assuming you have the timing correct, one way to confirm whether the cam profile is correct for your current setup is to substitute low-tension in./ex. springs in place of the factory spring - light enough to open the valves with finger pressure. Only one cylinder (no.1 or 4) should contain springs so the engine can rotate easily during this inspection.

Create a chart to track in./ex. valve lift along with piston travel in crank degrees, with/without deck height clearance. This should confirm if your cam specs are too aggressive, then proceed accordingly with a more compatible grind and/or add'l cylinder base spacers while maintaining the ideal/desired deck height/compression ratio.

Sherwood

camgrinder · 06-15-2009, 11:48 AM

How far after TDC are you having the contact? The checking method you are using can cause the valve spring retainer to hit the guide seal. If the heads are set up with less than 1.5 mm clearance between the retainer and the seal at full valve lift, you will be very close.

914TWO · 06-16-2009, 04:54 AM

Hi to all who are trying to help me out here. I work a second job to maintain this project as the hobby I want it to be, and have long days that make my replies to your thoughts a little slow. I will try and get back to you in a more timely fashion. Thanks for sticking with me.

First to Sherwood, I did try the lighter springs as mentioned, but found that I had a problem setting the cam timing properly, as I noticed the dial gauge would cause the retainer to move slightly from the pressure and throw off the reading. I could not get the valve spring retainer to snap up into the keepers so that it would sit stable and not be moved by just the pressure from the gauge. The valves that were in stalled, and the keepers, only have one groove in them instead of the 2 like the stock ones, and maybe that is why I had that problem. I thought I would try Waynes idea of the zero lash once things were set, and rotate the engine through its cycle checking it along the way. As I mentioned with the original .25 base gasket, which gave me a deck height of roughly 1.5mm, I could not get seem to get any clearance at all with the exhaust valve. Now that I have changed the base gaskets to 1.5mm, which I guess now gives me roughly 3mm of deck height, I have solved the exhaust valve problem at even the 6.2mm timing, but the intake valve will not have the proper clearance.

John I will check your idea of the retainer hitting the guide seal, as I would have not thought of that problem. I will also go back and re-verify all measurements on clearances at 6.2, 6.0, 5.8mm valve timing and let you know what they come out as. Thanks again everyone.

Steve

cgarr · cgarr's Garage

Whats your method for measuring? From where to what?

BURN-BROS · 06-16-2009, 05:35 AM

Oversized valves?

jpnovak · 06-16-2009, 06:57 AM

Aaron beat me to the valve question...

2.0 heads with different valve angles and small, steep combustion chamber?

T77911S · 06-17-2009, 03:55 AM

Quote:

Originally Posted by 914TWO

as I noticed the dial gauge would cause the retainer to move slightly from the pressure and throw off the reading. I could not get the valve spring retainer to snap up into the keepers so that it would sit stable and not be moved by just the pressure from the gauge.

Steve

i may be off base here, but this does not sound right to me.

also, are you reading the dial gage properly. someone set mine way off because they missread the dial gage. the dial gage spins CCW as the valve opens. instead of setting mine at .020 (?) of lift, they set it so the needle went past .080(.020) down to .020, which was actually .080 of lift. my gage has 2 sets of numbers, one counts up CW and the other set counts up CCW, they used the CW set of numbers until the needle pointed at .020. kinda hard to explain.

914TWO · 06-17-2009, 10:07 PM

Hi All, thanks for all of your posts. I am burning the candle at both ends with work, and feel bad about being slow to respond to the posts, but I will try and answer as well as I can. To John I will check to make sure that there is not a problem with the spring retainer contacting the valve guide seal. I currently have the intake valve sitting close to the top of the lob, and can see what you mean, and will try and use a mirror to see if I can see if that is a problem.

To cgarr I am following the method in Wayne Dempsys book to check piston to valve clearance by setting the timing, then going back and setting valve lash to zero, and then turning in the valve adjustment screw to see where there may be clearance issues.

As to the question on the valve size, I was concerned about that also. My build sheet says they are 46mm in. and 40mm exhaust. I remember on one of my many times tearing things back apart I found that the intake diameter was the same as the stock valves that came out, but I will check that again. I did take one out and just set it in the piston pocket, and it does not seem to be a lot of clearance to me, but I would not know what would be a proper amount of clearance around the pocket. Also I am using the later heads, and in fact these started life as 2.4 mech. I also had the pistons Jet Hot coated before I started the project, and somewhere along my many checks of this clearance, I have run the valve down to touch the piston, and have rubbed the slightest circle from the center of the valve into the coating on the piston top, which seems to indicate that the valve is centered, and at the proper angle, but then again, if it was all correct I wouldn't find myself in this mess.

I also realized that using a mechanical dial gauge was going to be a bit of a challenge, so I opted for a digital one that allows me to set a pre-load on it, and then zero it from there so that the reading would not need me to keep track of how many times the needle rotated.

I am not crazy about tearing this back apart, but I have obviously missed something. I will take photos of what I have and post them in case it helps with any ideas. I really do appreciate all of your ideas, and patience for my slow replies. I hope to get to only burning that work candle from one end shortly. Thanks again.

Steve

914TWO · 06-25-2009, 06:24 PM

Hi All, I have quit burning the candle at both ends, and am able to get back to the project. If anyone is still following I have 2.2 liter heads to answer an earlier question, and I did the clay(playdough in my case) check to make sure the valves were laying perfectly in the cutouts on the pistons and they are. I have also used the lighter springs to make sure there is not any binding between the valve spring retainer and the oil seal on the valve. I have also just checked the deck height again since I have it all apart, and it verified what I thought and I now have a deck height of 2.7mm with all of the shims I put under the barrell to first try and fix this problem. Way too much deck height I know. I only seem to obviously find clearance if I keep backing off the valve timing, but I am not clear on what I am giving up performance wise by doing this.
The suggestion was also made that I may need to use a different cam, and if that is the case what cam would be a good substitute? This is a 2.2 race engine for PCA racing, and I am running a TEC III injection system. The heads are also twin plugged. Thanks for any suggestions.

Steve

camgrinder · 06-26-2009, 08:13 AM

Sounds like you need to cut deeper pockets in the pistons. Give me a call when you get a chance.

viejopatron · viejopatron's Garage

Call me a bedwetter, but when I got to this point on my rebuild I took the engine to a pro wrench to verify the clearance and timing. My rational was that with the time and money I've invested the risk was lower with another more experienced look-see.

911pcars · 06-27-2009, 08:26 AM

Quote:

Originally Posted by viejopatron

Call me a bedwetter, but when I got to this point on my rebuild I took the engine to a pro wrench to verify the clearance and timing. My rational was that with the time and money I've invested the risk was lower with another more experienced look-see.

There's no manhood lost in that decision. Lesser persons might have performed one of those backyard, good-enough procedures to make it work. The classifieds are littered with other peoples' botched solutions. Sometimes, all it takes is an objective POV to reveal a solution; other times, it's more complicated.

Let us know how it turns out.

Sherwood

914TWO · 06-27-2009, 07:53 PM

Hi Guys,

First of all John I will call you to see what thoughts you have, and to Gary and Sherwood, I was having the same thought. There is a local builder who is a good friend, and I have only stopped by his busy shop to ask his opinion and see if there was some step I either missed or did incorrectly. He said it all sounded correct to him, but obviously he did not have the benefit of actually seeing the engine. I guess that time has come. I will post what turns out to be the solution to this problem, and somehow I figure it will come back to rookie engine builder error.

Steve