XR70 top end upgrade

[surveywaters]

I need to replace the rings on my boys 70.

I figure I might as well go on and do the 88cc bore.
Looks like this would require a hi volume oil pump.
Probably should go ahead and get the 20mm carb and intake which may require a new throttle cable.
A lot of these kits come with cams, is this worth the money and will the bike maintain reliability after all this?
Can I continue to use my stock exhaust?

There is an over whelming number of options out there, but I don't want to spend $400.

Who have you guys purchased from that you would or would not deal with again?

 

[surveywaters]

Is this overkil, it is really pushing the budget. Also, anyone know if brandXminis sells quality parts?

 

[The_GDFP]

B-X is so-so at best. No customer service or product support. The manifold is too small, filter junk. TB kit is a couple bucks more, but worth every penny.

On a budget, TB 88 kit and the stock head and 17mm carb is a ton stronger than stock low-compression deal. Add some valve seals and a cam chain for good measure. Shhh, but your 70 has a higher volume oil pump and stouter clutch than the 50's already TB 3-disk plates in the stock basket, works great, if yours wears out with the extra torque.

 

[SnItChY]

+1 For Terry ....you wont go wrong

 

[doopsx3]

B-X is so NO!!!! Complete junk......go TB and you will not be sorry.....go FPM and you will not be sorry as well

 

[surveywaters]

Shhh, but your 70 has a higher volume oil pump and stouter clutch than the 50's already;

So I don't need the oil pump? I know the $25 isn't much but they add up. I would rather use that for a new DID cam chain.

I appreciate the input, this is exactly what I wanted to know. I will definetly be going TB.

 

[surveywaters]

By the time I do all this, I could just get this 110cc ssr or this 86cc piranha with everything including a carb.

Which would be stronger, the modified Honda or one of these?

 

[The_GDFP]

Your stock head and 88 kit would be stronger than either crate engine. Adding the race head, it's no contest.

But, the Piranha/YX 90 is a nice option. T-Bag isn't a forum supporter, FWIW
Piranha YX 90cc Engine

 

[surveywaters]

I apreciate the response and advice GDFP. I think I'll stick with the honda case and put the 88cc jug, Hi comp piston, reprofiled cam, and the 20mm carb on, plus a new cam chain. That will run me around $250 +s/h.

Now I just need to know if my factory exhaust will be okay for a while cause this will leave me broke.

 

[The_GDFP]

Stock pipe will be fine. Shipping is free, if you're in the US.

 

[doopsx3]

You will like the REAL HONDA with a 88 on it....fun and Honda reliable

p.s. support the peeps that support this forum.....please

 

[surveywaters]

I have already made arrangements with ....he who must not be named... on the 88 kit. However, I have ordered everything else I feel I'll be needing from Fire Power Minis to spread it around a bit.

Now we'll see who ships faster

Thanks for all the help guys.


Jon

 

[Kurlon]

On the stock pipe, pop it off and look at the intake end. You'll see a messy weld choking it off. Get a grinding stone for your dremel and grind that puppy down. At the other end, you can remove the spark arrestor for a lil more flow but only do it if you don't ride where fire is a concern.

On the clutch, pull it apart and look at the weights. Those wasteful, heavy weights... Replace them with Powroll's TI versions, or carefully drill a hole in the fat portion of each to reduce their weight. Deburr them nicely after drilling. This will raise the engagement RPM and make even a stock 70 'peppier', it's a blast if your motor has some umph to it.

 

[surveywaters]

thanks for the tips. I have already honed the exhaust and remove the spark arrestor, but I haven't found a working link for the clutch mod. I've done this on my Lt80, but all I had to do was remove weigths. I drill these puppies out asap!

 

[hman]

i thought an XR engine was uprite??

 

[surveywaters]

XR 50's and XR 70's are horizontal, 75's and up are vertical.

 

[surveywaters]

I got my parts from FPM and everything is there and lookis good!

I discovered why I am having to replace the topend on this bike. I noticed excessive cam chain noise when I bought it a month or two ago. Apparently someone had removed the cam chain tensioner accidentally and then after reinstalling, failed to prime the hydraulic cylinder causing an inefficient tension, resulting in a worn out oil pump drive sprocket. I have heard of this on many other 70's and would say that anyone doing a topend would be wise to go ahead and replace this gear as well as the tensioner spring which seems to fail with out the assistance of the hydraulics.

 

[The_GDFP]

Glad it made it OK. I've seen the wear issue, plenty. I've found that the tensioner will quickly re-fill and work soon after fire-up, even if assembled empty. Unless, the check valve in the bottom is faulty. What I've seen, is a worn cam chain, on about every 70. The OE chain is light and stretches easily. The 70 has a higher-volume oil pump and bigger cam, both adding drag and speeding the chain's demise. The stock crank and cam sprockets are a lot tougher and seem to fare well, but the pump sprocket is dead-soft. I have a bunch of good used ones, if needed. New is about $18 from Honda.

 

[surveywaters]

I pulled a barely used gear out of a clone 70. I also used the clone's tensioner spring, it was a good bit stiffer.

I hope I didn't make a mistake buying the D.I.D. chain from you, I didn't know anything about the oem being weak.

Do new top ends usually smoke a bit while the rings are seating? I followed the TB install directions which called for a wet install; I typically go dry and have not seen the smoking.

 

[The_GDFP]

There are 68g and 86g chains. I only supply the 86 gram ones. Many stockers have the light one. Not as strong, and those are the ones I see in the worst shape.

Hopefully, it's just the guide and bore lube burning off. Smoking should stop with a few minutes of running and a light load to seat the rings.