Topic: Need help with a 970 big bore project

[slikwilli420]

Tdc needs to be found with a piston stop. Timing could be part of the interference issue. What cam is it again?

[calj737]

Better pull the head and use machinists clay or similar to measure the exact depth and relief cut that may be required in your pistons if the head gasket is not suitable for taking out the space. Spacing the gasket too thick diminishes the merits of the engine you’ve built as a consequence.

[awiertalla]

Tdc needs to be found with a piston stop. Timing could be part of the interference issue. What cam is it again?

I did the piston stop way the first time, but someone else on here said that was incorrect. I used an old spark plug, welded a bolt on, touched the piston to it one direction, marked that on my degree wheel. Then rotated it till it touched the other direction and marked it again. Some math involved and I came up with my tdc.

This time I am following Santanic Mechanics guideline for degreeing a camshaft, and it says to remove the head and place dial indicator on piston top. That way I can find exact tdc and how many degrees it stays on tdc for, which I did as well with the piston stop. But I am all for learning multiple ways of doing things. This is still all pretty new to me.

The cam installed is a Kenny Harmon D-grind. I pulled the specs of Satanic Mechanics website.

[awiertalla]

Tdc needs to be found with a piston stop. Timing could be part of the interference issue. What cam is it again?

The other thing is, I now have oversized stainless valves, which I didn’t the last time I assembled and attempted to start it. Could that also cause interference? I was leaning towards valve timing, seeing as it was only 1 and 4 that was making contact.

[calj737]

Yes, oversized valves change interference specs.

[754]

Thicker gasket maybe, but you need 45 thou or more clearance.
 If you pull the pistons, then you can mill them.
That should be checked on assembly, I think you got lucky...

[Jerry Rxman Griffin aka MuthaF'er]

I am using a RC315/DP315 cam in my 1000 with 33.5mm intakes without issues (so far). I have a Megacycle 125/75 in my 900 with 34mm intakes without problems. Just make sure you are setting up/degreeing the cam properly.

Right now my biggest issue is setting up the wonderful DAMN Webers LOL

[kmb69]

Tdc needs to be found with a piston stop. Timing could be part of the interference issue. What cam is it again?

I did the piston stop way the first time, but someone else on here said that was incorrect. I used an old spark plug, welded a bolt on, touched the piston to it one direction, marked that on my degree wheel. Then rotated it till it touched the other direction and marked it again. Some math involved and I came up with my tdc.

This time I am following Santanic Mechanics guideline for degreeing a camshaft, and it says to remove the head and place dial indicator on piston top. That way I can find exact tdc and how many degrees it stays on tdc for, which I did as well with the piston stop. But I am all for learning multiple ways of doing things. This is still all pretty new to me.

The cam installed is a Kenny Harmon D-grind. I pulled the specs of Satanic Mechanics website.

Matt is correct about using the piston stop. It is a more accurate method to measure the rotational difference, no "float" at TDC, IMHO.
Axel's (RIP) method requires similar calculations and you have the float introducing potential uncertainty at TDC to contend with.

[scottly]

The other thing is, I now have oversized stainless valves, which I didn’t the last time I assembled and attempted to start it. Could that also cause interference? I was leaning towards valve timing, seeing as it was only 1 and 4 that was making contact.

Yes, oversized valves will reduce clearance, but valve timing would affect all four cylinders the same. The valve cutouts are not symmetrical; do you have the 1 and 4 pistons reversed?

[awiertalla]

The other thing is, I now have oversized stainless valves, which I didn’t the last time I assembled and attempted to start it. Could that also cause interference? I was leaning towards valve timing, seeing as it was only 1 and 4 that was making contact.

Yes, oversized valves will reduce clearance, but valve timing would affect all four cylinders the same. The valve cutouts are not symmetrical; do you have the 1 and 4 pistons reversed?

Not to my knowledge, but my knowledge is minimal compared to you guys. I shall check this when I have some time to throw at the bike again. It might not be until next week at this point. Ill snap and post a photo of the pistons and how they are installed. I installed the pistons into the cylinders almost 2 years ago, so I cant be sure off hand.

[awiertalla]

The other thing is, I now have oversized stainless valves, which I didn’t the last time I assembled and attempted to start it. Could that also cause interference? I was leaning towards valve timing, seeing as it was only 1 and 4 that was making contact.

Yes, oversized valves will reduce clearance, but valve timing would affect all four cylinders the same. The valve cutouts are not symmetrical; do you have the 1 and 4 pistons reversed?

To my dismay, you appear to be correct. I had installed the 1 and 2 facing one way, 3 and 4 the other way. You were absolutely right, I need to swap 1 and 4, and correct my valve timing. Thank you for your input, I would’nt have realized this.

[MRieck]

Better to find and correct now. And.....you are not the first person to do this.

[scottly]

Check for bent valves: the quick and dirty method with the engine apart is to set the head upside down and fill the combustion chambers with gasoline, and see it it runs out the ports. NO smoking while testing!
Do clay the pistons to check for adequate valve to piston clearance.
If spark-plugs were installed when the motor was turned, check the gap, as the pistons might have hit the ground strap.

[PeWe]

When assembled, before valve cover is mounted:
Important to rotate the crank several times when cam and rockers are installed, no plugs in. You’ll feel if pistons kiss the valves.
I think it is 15 degees before and after TDC the valve- piston clearance must be checked. I continue to tighten the adjuster screws. If OK to adjust them 2mm further down without stop hitting the piston, I’m relaxed.
I usually time in 1 first, then ex 1, followed by in 1 again to ensure same values as first time. If different, start over again. It is cheaper to rotate the crank and check cam timing and valve- piston clearance several times to be sure.

Pistons that have angled pockets are compared with head. I check many times to be sure. Hold head over and look. Clay test reveal mistakes.
Older pistons could have different weight. I matched them: 1&4 same weight as 2&3, 1 same weight as meeting 2, 4 same as meeting 3.

[Bill/BentON Racing]

Good luck, some seems to have come your way already.  K. Keep asking questions,  you are learning. Bigger valves will be closer to each other on overlap and more likely to have valve to valve contact.Was going to ask to see pistons tops, but ya'll figured it out.  Definitely not the first as Mike stated. You'll get it! Keep us posted,  Bill

[awiertalla]

Good luck, some seems to have come your way already.  K. Keep asking questions,  you are learning. Bigger valves will be closer to each other on overlap and more likely to have valve to valve contact.Was going to ask to see pistons tops, but ya'll figured it out.  Definitely not the first as Mike stated. You'll get it! Keep us posted,  Bill

I sincerely appreciate the support. It can be difficult to post on the forums knowing that you guys are so knowledgeable and I am asking what seem like stupid questions.

As for the bike, I swapped the pistons and lost a wrist pin so had to order new ones (I should replace those 4 anyways since I removed them).

I also used permatex on the base gasket when I installed it, and I’ve torqued the head down 4 or 5 times now. I think I am going to reassemble using all the old gaskets, so I can trouble shoot, and once it runs (if and when it leaks) I will have a complete top end gasket set waiting to install. I am just figuring I will have to disassemble it at least one more time for some small thing or another. Does this all make sense, or am I being overly sensitive and should I reassemble using all new gaskets?

[Jerry Rxman Griffin aka MuthaF'er]

The old gaskets MAY be fine but it will be a royal PITA to replace if they leak. Put in a frame kit.

Why Permatex??!! You're asking for trouble. Gaskets should go on dry.

[awiertalla]

The old gaskets MAY be fine but it will be a royal PITA to replace if they leak. Put in a frame kit.

Why Permatex??!! You're asking for trouble. Gaskets should go on dry.

It was told to me by another mechanic to use on stuff like base gaskets. That was the first (and most likely the last time) I used it. It is definitely a pain in the ass. I am going to buy another Cyclex topend gasket set for it, plan on getting the motor running, then do a top end rebuild. I already have an oil leak because I skipped replacing my neutral switch seal under the motor, the screw was stripped, so I am pretty sure I will have to pull the engine to get that out properly.

[MRieck]

Neutral switch can be changed with the engine in the frame

[PeWe]

Neutral switch can be changed with the engine in the frame

Important to replace o-ring 18x3 that must go in case before switch. O-ring on switch, impossible to get switch in. Lube the o-ring will help.

[Jerry Rxman Griffin aka MuthaF'er]

Might have to jiggle the shift drum apparatus behind the shifter cover to help remove/replace the switch too.

[Bill/BentON Racing]

Neutral switch can be changed with the engine in the frame

Important to replace o-ring 18x3 that must go in case before switch. O-ring on switch, impossible to get switch in. Lube the o-ring will help.

+1 Lol. That ain't in the book!

[PeWe]

Neutral switch can be changed with the engine in the frame

Important to replace o-ring 18x3 that must go in case before switch. O-ring on switch, impossible to get switch in. Lube the o-ring will help.

+1 Lol. That ain't in the book!

Yeah! Good to know before looking for the sledgehammer! $$$$

[awiertalla]

Can you guys clarify the correct way to advance or retard the camshaft. I flipped my pistons, set them again and will be installing my cam and degreeing it this weekend, but want to do it correctly this time.

I plan on setting my crank and pistons to tdc, installing the cam with the notch upwards and line parrallel, from there use the stock sprocket holes as temp install to get it lined up. Once it’s line up, I would remove sprocket bolts leaving the sprocket on the shoulder of the cam, and carefully rotate the cam until it lines up with the 8 degree advance hole.

In my mind, that leaves tdc correct but adjusts the time the cam opens the valves in relation to tdc. Once I have that done, I was going to mark a parallel line on the cam end, and swap out my old R.C sprocket (with predrilled -5 and 8 holes) with the new adjustable one I bought in order to fine tune it.

Thoughts and feelings about this?

[NitroHunter]

I degree cams by the lobe center, using the manufacturers supplied cam card as a reference.
TDC piston using the positive stopper method. Install the cam as you described, using your adjustable sprocket from the outset. This will get you close. Zero lash #1 intake. You read your opening and closing numbers at whatever lift figure the card gives you, but using this LC method it won't matter if you used .040" or .050" valve lift as these SOHC cam lobe profiles aren't so extreme. The opening and closing numbers would be slightly different, but THE LOBE CENTER will remain the same.
Intake: Opening # + 180 + Closing #, divide that sum by 2, now subtract the opening #. This will give you the LC figure for the intake and should match the card.
Here is an example I have in front of me, sorry not a SOHC (it's a Chrysler 426) but this shows you how it works with all engines. The numbers will be different but the math is the same.
Bullet Cam card states degree the intake lobe to 112 Lobe Center.
 At .050" lift I open at 36* BTDC, rotate 180*, then close at 80.
 36 + 180 + 80 = 296.
296 / 2 = 148
148 - 36 = 112 LC
If you play with the opening number, you can see how the LC changes. Your desired LC will determine your opening number.
Found this for an RC 315, it's advertised as a 104LC. The math works the same.
Open 23 + 180 + Close 53
Hope this helps. And yeah those old multi-drilled RC sprockets were 'challenging' to say the least.