Different timing belt lengths: followup
07-21-2004, 11:12 AM
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Different timing belt lengths: followup
A note here to help out anyone who may run into the same problem --
I did a timing belt job on my B18C1 GSR a few months ago. By mistake, I ended up with a B18C5 Type-R timing belt instead. I noticed that the new belt was about 5cm longer overall, but I was (foolishly) confident enough not to triplecheck my part numbers.
As for why the C5 belt is longer than the C1 belt, someone suggested elsewhere on HA-net that the C5 head is slightly taller. I can't speak to that issue with any authority, but it sounds right. But the interesting thing to me was what happened with the longer belt in the motor.
There turn out to be two problems with that. One is that the distributor drive lug is going to rattle loudly from insufficient tension, given the longer belt. That was what first clued me in to the fact that I had a problem. This can be patched around by having a helper snag the belt tensioner spring with a long wire tool (i.e., coat hanger) and pull up firmly during the normal post-install belt tensioning procedure.
Even if you do this (which gets rid of the distributor rattle and other symptoms of lack of tension), there is a second, harder problem. The B18C1 and B18C5 belts differ in overall length, but they have the same number of teeth, 126.
This means that the intertooth spacing is slightly wider on the longer belt. I found that what that translated into, in terms of a C5 belt on a C1 motor, was that the cams were slightly behind the crank. When the crank was at TDC1, the cams were still a few degrees away from their own TDC1. When the cams got to their own TDC1, the crank had moved a few degrees ahead.
Effectively what the longer belt does is to artificially dial in some retard. And the engine showed behavior consistent with that: boggy at low revs, reduced top end power, no detonation even on watery 87 octane pump gas.
I wondered if adjustable cam gears would fix it, and dug up some JG ones (nice pieces, by the way). I've spent the last week experimenting, and now have both cams running with between 3.5 and 4 degrees of advance. That seems to be equivalent to stock cam timing.
The motor no longer bogs at low RPM, it makes clean power to redline, and it is back to detonating on anything other than premium fuel. In fact, it detonates on premium, which is what it did with the stock belt, but remember that this is horrible 91 octane California "premium", ugh.
This probably should not be used as a long-term solution. There may be other issues that could possibly lead to an early belt failure or other expensive problems. I plan to swap out this C5 belt for the correct C1 belt later on in the fall, when the car goes offline for suspension work.
I have gone through all this because the belt-length issue might come up in other contexts and make problems for people. It's theoretically possible that someone might end up with the reverse mixup, a C1 belt on a C5 motor.
In that case, the shorter belt than spec would result in possibly too much tension instead of too little (risk of belt failure or bearing damage). It would also result in artificially induced cam timing advance, instead of retard, and on a highly tuned C5, that might cause head damage.
And this is with factory belts. The aftermarket is a whole 'nother story. Both Greddy and Toda sell "high power" timing belts for these engines. Neither one bother to make a specific belt for the B18C1 and another specific belt for the B18C5 -- they just sell a generic "B18C" belt.
I haven't measured either one of these aftermarket belts. There are some smart cookies at Toda and at Greddy, but the fundamental issue here is with engine dimensions, and a belt that fits one of these two engines perfectly is by definition going to be imperfect on the other. Perhaps the aftermarket guys have taken an average of the two lengths (which means that such a belt will be suboptimal on both engine types). Or perhaps they're assuming that anyone who buys a high-power belt is going to have adjustable cam gears already (a risky assumption, for sure).
What you should do as an informed parts consumer is to be aware of belt length as an issue, ask tough questions in advance, and be prepared to take adaptive steps like using adjustable cam gears, just in case.
Hope that's valuable for someone. I really wish I'd been clued in to this ahead of time; if I can save time for others, that will make up for some of the time that I wasted in puzzling my way through this!
I did a timing belt job on my B18C1 GSR a few months ago. By mistake, I ended up with a B18C5 Type-R timing belt instead. I noticed that the new belt was about 5cm longer overall, but I was (foolishly) confident enough not to triplecheck my part numbers.
As for why the C5 belt is longer than the C1 belt, someone suggested elsewhere on HA-net that the C5 head is slightly taller. I can't speak to that issue with any authority, but it sounds right. But the interesting thing to me was what happened with the longer belt in the motor.
There turn out to be two problems with that. One is that the distributor drive lug is going to rattle loudly from insufficient tension, given the longer belt. That was what first clued me in to the fact that I had a problem. This can be patched around by having a helper snag the belt tensioner spring with a long wire tool (i.e., coat hanger) and pull up firmly during the normal post-install belt tensioning procedure.
Even if you do this (which gets rid of the distributor rattle and other symptoms of lack of tension), there is a second, harder problem. The B18C1 and B18C5 belts differ in overall length, but they have the same number of teeth, 126.
This means that the intertooth spacing is slightly wider on the longer belt. I found that what that translated into, in terms of a C5 belt on a C1 motor, was that the cams were slightly behind the crank. When the crank was at TDC1, the cams were still a few degrees away from their own TDC1. When the cams got to their own TDC1, the crank had moved a few degrees ahead.
Effectively what the longer belt does is to artificially dial in some retard. And the engine showed behavior consistent with that: boggy at low revs, reduced top end power, no detonation even on watery 87 octane pump gas.
I wondered if adjustable cam gears would fix it, and dug up some JG ones (nice pieces, by the way). I've spent the last week experimenting, and now have both cams running with between 3.5 and 4 degrees of advance. That seems to be equivalent to stock cam timing.
The motor no longer bogs at low RPM, it makes clean power to redline, and it is back to detonating on anything other than premium fuel. In fact, it detonates on premium, which is what it did with the stock belt, but remember that this is horrible 91 octane California "premium", ugh.
This probably should not be used as a long-term solution. There may be other issues that could possibly lead to an early belt failure or other expensive problems. I plan to swap out this C5 belt for the correct C1 belt later on in the fall, when the car goes offline for suspension work.
I have gone through all this because the belt-length issue might come up in other contexts and make problems for people. It's theoretically possible that someone might end up with the reverse mixup, a C1 belt on a C5 motor.
In that case, the shorter belt than spec would result in possibly too much tension instead of too little (risk of belt failure or bearing damage). It would also result in artificially induced cam timing advance, instead of retard, and on a highly tuned C5, that might cause head damage.
And this is with factory belts. The aftermarket is a whole 'nother story. Both Greddy and Toda sell "high power" timing belts for these engines. Neither one bother to make a specific belt for the B18C1 and another specific belt for the B18C5 -- they just sell a generic "B18C" belt.
I haven't measured either one of these aftermarket belts. There are some smart cookies at Toda and at Greddy, but the fundamental issue here is with engine dimensions, and a belt that fits one of these two engines perfectly is by definition going to be imperfect on the other. Perhaps the aftermarket guys have taken an average of the two lengths (which means that such a belt will be suboptimal on both engine types). Or perhaps they're assuming that anyone who buys a high-power belt is going to have adjustable cam gears already (a risky assumption, for sure).
What you should do as an informed parts consumer is to be aware of belt length as an issue, ask tough questions in advance, and be prepared to take adaptive steps like using adjustable cam gears, just in case.
Hope that's valuable for someone. I really wish I'd been clued in to this ahead of time; if I can save time for others, that will make up for some of the time that I wasted in puzzling my way through this!
07-25-2004, 12:27 PM
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Originally Posted by b16aEGcivic
if you use the type R pump and belt, then it would work....you have to use the respective belt to the respective pump
This guy put a lot of research into this, let's not cloud it up with assumptions.
-PHiZ
07-25-2004, 09:53 PM
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Originally Posted by PHiZ
Do you have part numbers to back up this statment? Remember the B18C lower ends are the same, I bet they both have a "p72" part number for the pumps. It's the heads that are different P72 vs PR3 casting...
This guy put a lot of research into this, let's not cloud it up with assumptions.
-PHiZ
This guy put a lot of research into this, let's not cloud it up with assumptions.
-PHiZ
07-26-2004, 11:41 PM
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Originally Posted by b16aEGcivic
just from experience...put a Type R pump with Type R belt on my buddies GSR a couple weeks ago.
-PHiZ